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Systems And Components In Commercial Vehicles
2. Edition
Copyright WABCO 2005
Vehicle Control SystemsAn American Standard Company
The right of amendment is reservedVersion 002/09.01(en)
8150100033 815 010 003 3
31
Page
Operation of Air Braking Systems ..................................................... 4
1. Motor VehiclesBraking System ............................................................................. 6Components of the Motor Vehicle’s Braking System........................... 7
2. TrailersBraking System ........................................................................... 64Equipment For Trailer Braking Systems ............................................ 66
3. Anti-Lock Braking System (ABS) .................................................... 83
4. Sustained-Action Braking Systems On Motor Vehicles ................ 95
5. EBS - Elektronisch geregeltes Bremssystem ............................... 101
6. Air Suspension Systems and ECAS (Electronically Controlled Air Suspension)................................... 111
7. Clutch Servo..................................................................................... 123
8. Air Braking Systems In Agricultural Vehicles ....................................................................... 127
9. ETS and MTS - Elektronic Door Control Systems For Motor Coaches .......................................................................... 137
10. Installation Of Pipes And Screw Unions ....................................... 151
11. Index ................................................................................................. 163
Table of Contents
4
Operation of Air Braking Systems
1. Compressed Air Supply
The compressed air supplied by the com-pressor (1) flows to the air dryer (3) viathe unloader (2) which automatically con-trols the pressure within the system with-in a range of between 7.2 and 8.1 bar, forinstance. In the air dryer, the water va-pour in the air is extracted and expelledthrough the air dryer’s vent. The dried airthen flows to the quadruple-circuit pro-tection valve (4) which, if one or severalcircuits are defective, secures the intactcircuits against any loss in pressure.Within the service braking circuits I andII, the air supply from the reservoirs (6and 7) flows to the brake valve (15). InCircuit III the air supply from the reservoir(5) flows through the 2/2-way valve whichis integrated in the trailer control valve(17) to the automatic hose coupling (11)and on to the check valve (13), the handbrake valve (16) and the relay valve (20)into the spring-loaded portion of the Tris-top spring brake actuators (19). Circuit IVsupplies air to any ancillary consumers,in this case an exhaust brake.
The trailer’s braking system receivescompressed air through the hose cou-pling (11) with its supply hose connected.This air then passes the line filter (25)
and the relay emergency valve (27) be-fore reaching the reservoir (28) and alsoflows to the supply ports of the ABS relayvalves (38).
2. Operation:
2.1 Service Braking SystemWhen the brake valve (15) is actuated,compressed air flows via the ABS sole-noid control valve (39) into the brakechambers (14) of the front axle and to theload-sensing valve (18). This valve re-verses and the air flows via the ABS so-lenoid control valve (40) into the servicebrake portion (brake chambers) of theTristop spring brake actuators (19). Thepressure in the brake cylinders generat-ing the force required for the wheel brakedepends on the amount of force appliedto the brake valve, and on the load car-ried on the vehicle. This brake pressureis controlled by the load-sensing valve(18) which is connected to the rear axleby means of a linkage. Any change in thedistance between the vehicle’s chassisand its axle caused by loading or unload-ing the vehicle causes the brake pres-sure to be continuously adjusted. At thesame time, via a pilot line, the load-emptyvalve integrated in the brake valve is af-fected by the load-sensing valve. Thus
the brake pressure on the front axle isalso adjusted to the load carried on thevehicle (mostly on lorries).
The trailer control valve (17) actuated bythe two service braking circuits pressuriz-es the pilot connection of the relay emer-gency valve (27) after passing the hosecoupling (12) and the connecting “con-trol“ hose. The air supply from the air res-ervoir (28) is thus allowed to passthrough the relay-emergency valve, thetrailer release valve (32), the adaptervalve (33) and on to the load-sensingvalve (34) and the ABS relay valve (37).The relay valve (37) is actuated by theload-sensing valve (34) and the com-pressed air flows to the brake chambers(29) on the front axle. The ABS relayvalves (38) are actuated by the load-sensing valve (35), and the compressedair is allowed to pass to the brake cham-bers (30 and 31). The service pressureon the trailer, which is similar to the out-put pressure from the towing vehicle, isautomatically adjusted by the load-sens-ing valves (34 and 35) for the load carriedon the trailer. In order to prevent overb-raking of the wheel brake on the frontaxle in the partial-braking range, theservice pressure is reduced by the adapt-er valve (33). The ABS relay valves (on
5
the trailer) and the ABS solenoid controlvalves (on the towing vehicle) are used tocontrol (pressure increase, pressurehold, pressure release) the brake cylin-ders. If these valves are activated by theABS ECU (36 or 41), this control processis achieved regardless of the pressure al-lowed to pass by the brake valve or therelay emergency valve.
When they are not needed (solenoids aredead), the valves operate as relay valvesand achieve a faster increase or de-crease of the pressure for the brake cyl-inders.
2.2 Parking Braking SystemWhen the hand brake valve (16) is actu-ated and locked, the spring-loaded por-tions of the Tristop spring brakeactuators (19) are exhausted fully. Theforce needed for the wheel brake is nowprovided by the heavily preloadedsprings of the Tristop spring brake actua-tors. At the same time, the pressure inthe line leading from the hand brakevalve (16) to the trailer control valve (17)is reduced. Braking of the trailer com-mences by the pressure increasing in theconnecting ‘supply’ hose. Since theguideline of the Council of the EuropeanCommunities (RREG) that a tractor-trail-
er combination must be held by the motorvehicle alone, the pressure in the trailer’sbraking system can be released by mov-ing the hand brake lever into its ‘control’position. This permits the parking brakingsystem to be examined as to whether itfulfills the provisions of the RREG.
2.3 Auxiliary Braking SystemDue to sensitive graduation of the handbrake valve (16) the lorry can be brakedby means of the spring-loaded portionseven if the service braking systems I andII have failed. The brake force for thewheel brake is produced by the force ofthe preloaded springs of the Tristopspring brake actuators (19) as describedunder ‘Parking Braking System’ althoughthe spring-loaded portions are not ex-hausted fully but only to the extent re-quired for the braking performance.
3. Automatic Braking of the Trailer
In the event of the connecting ‘supply’line breaking, the pressure will drop rap-idly and the relay emergency valve (27)will cause full application of the trailer’sbrakes. In the event of the connecting‘control’ line breaking, the 2/2-way valveintegrated in the trailer control valve (17)
will, when the service braking system isactuated, throttle the passage of the sup-ply line leading to the hose coupling (11)to such an extent that the rupture of thesupply line causes a rapid drop in pres-sure in the supply line and the relayemergency valve (27) causes the trailerto be braked automatically within the le-gally stipulated time of no more than 2seconds. The check valve (13) securesthe parking braking system against anyinadvertent actuation if the pressuredrops in the supply line leading to thetrailer.
4. ABS ComponentsThe motor vehicle usually has three tell-tale lamps (ASR having one additionallamp) fitted for indicating functions andfor continuously monitoring the system. Italso has a relay, an information moduleand an ABS socket (24).
After actuating the driving switch, the yel-low telltale lamp will come on if the trailerhas no ABS or if the connection has notbeen established. The red lamp will go offwhen the vehicle exceeds a speed of ap-prox. 7 k.p.h. and the safety circuit of theABS electronics has not detected an er-ror.
Operation of Air Braking Systems
6
Air braking system with ABS/ASR (4S/4M)
Legend:
Pos.1 Compressor2 Air dryer with combined
unloader3 Four circuit protection valve4 Air reservoir5 Clamps6 Test coupling7 Drain valve8 Check valve9 Brake valve with integral
auto load proportioning valve10 Hand control valve with
trailer control11 Relay valve12 Piston cylinder13 Brake chamber14 ASR-Control cylinder
15 3/2 Solenoid valve16 Tristop-Brake actuator17 Quick release valve18 Load sensing valve19 Knuckle joint20 Trailer control valve21 Hose coupling, supply22 Hose coupling, control23 Two-Way valve24 ABS Warning lamp25 ABS Info lamp26 ABS-socket27 Sensor extension cable28 Solenoid cable29 Socket 30 Sensor braket
31 Sensor with cable32 Pole wheel33 ABS-Solenoid valve34 Electronic control unit35 Info module36 Pressure switch37 Proportional valve38 3/2 Directional control valve
1238
1
2 3
4,5
7
14
37
917
13
33
28
2729,3031,32
24
25
34 35
18
19 15
6
26
11
23
16
21
2220
10
8
36
7
1.
Components Of TheMotor Vehicle’s Braking System
8
Air Intake Filters1.
Moist Air Filter
Purpose:To prevent impurities from the air gettinginto the compressor (by using suction fil-ters) or into the vents of compressed airequipment (by using vent filters); theyalso serve to muffle the noise caused bythe intake of air or by blowing it off.
Operation:Moist air filters (for normal operating con-ditions). The air is taken in through anopening in the cap, flows through the fil-ter medium where it is cleaned and thenflows on to the air intake of the compres-sor.
Oil Bath Air Cleaner
Operation:Oil bath air cleaner (for air containing alarge mount of dust)
The air is taken in through the sieve platebelow the cap and the central pipe, andthen passed across the surface of the oilwhere any dust particles can settle. Fromthe surface of the oil, the air is pushedupward, flows through a filter packagewhich retains any impurities which maystill be contained in the air and any oilparticles carried over before reachingthe air intake of the compressor.
Moist Air Filter432 600 . . . 0 to 432 607 . . . 0
Oil Bath Air Cleaner432 693 . . . 0 to 432 699 . . . 0
9
Purpose:Production of compressed air for roadvehicles and static systems.
Operation:The pulley on the end of the crankshaft isrotated by a vee-belt driven off the vehi-cle’s engine. This rotation causes theconnecting rods to to move the pistons.As the piston travels downwards clean
air from either the engine air cleaner orthe moist air filter (or alternatively an oilbath air cleaner) is drawn in trough theinlet valve. As the piston moves up-wards, the inlet valve closes, and air ispumped through the delivery valve intothe the reservoir.
The type of lubrication depends on theconstruction of the compressor, and canbe splash or pressure fed.
Compressor 1.Single CylinderAir Compressor 411 1 . . . . . 0 and 911 . . . . . . 0
Twin CylinderAir Compressor411 5 . . . . . 0 and 911 5 . . . . . 0
10
Air Cleaner1.
Purpose:To clean the air delivered by the com-pressor and to precipitate the humidity itcontains.
Operation:The air entering at port 1 flows throughannular gap A into Chamber B. As itpasses through the gap A, the air coolsand some of the water vapour it containswill condensate. The air then flowsthrough the filter (a) to Port 2.
At the same time, the pressure in Cham-ber B opens the inlet (3) of the valvebody (d) and the condensate runsthrough the filter (f) into Chamber C. As
the pressure in Chamber B falls, the inlet(3) closes and the outlet (b) opens. Thecondensate is now blown outside by thepressure in Chamber C. When the pres-sures in Chambers B and C are bal-anced, outlet (b) closes.
Pin (C) can be used to check whether theautomatic drain valve is working proper-ly.
Air Cleaner432 511 . . . 0
11
Air Dryer432 410 . . . 0 and 432 420 . . . 0
Purpose: Drying of the compressed air supplied bythe compressor by extracting the mois-ture present in the air. This is effected bya progress of cold regenerated adsorp-tion drying where the air compressed bythe compressor is led through granulates(adsorbens) capable of adsorbing themoisture contained in the air.
Operation:Variant 1 (Control Via Separate Un-loader Valve 432 420 ... 0)
In the feed phase, the compressed airsupplied by the compressor flows viaPort 1 into Chamber A. Here the conden-sate caused by the reduction in tempera-ture will collect, reaching Outlet (e) viaDuct C.
Via Fine Filter (g) integrated in the car-tridge, and via Annulus (h), the air willreach the upper side of Desiccant Car-trige (b), being cooled in the process,and further condensate will precipitate.Moisture is extracted from the air as itpasses through Granulate (a) this mois-ture is absorbed by the surface and the
fine ducts [diameter: 4 x 106 m = 4Å(Angström)] of the extremely porousgranulate.Since the oil molecules are more than 4Åin size they cannot enter the fine ducts ofthe granulates. This makes the granulaterobust. The steam portion of the oil is notadsorbed. The dried air reaches the airreservoirs via Check Valve (c) and Port21. At the same time, the dried air alsoreaches the re-generation reservoir viathrottling port and Port 22.
When cut-out pressure in the system isreached, Chamber B is pressurized fromthe unloader valve via Port 4. Piston (d)moves downwards, opening Outlet (e).The air, the condensate plus any impuri-ties and oil carbon from Chamber A willbe emitted via Duct C and Outlet (e).
When cut-in pressure at the unloadervalve is reached, Chamber B is ventedonce again. Outlet (e) closes and the dry-ing process will commence as describedabove.
Any malfunction due to icing in extremeconditions in the area of Piston (d) canbe prevented by fitting a Heating Car-tridge (g) which will switch on at temper-atures below 6°C and switch off againwhen the temperature reaches approx.30°C.
Variant 2 (Control Via Integral Unload-er Valve 432 410 ... 0)
The process of drying the air is as de-scribed under Variant 1 In this version,however, the cut-out pressure will reachChamber D via Bore (l), acting on Dia-phragm (m). After overcoming the springresistance, Inlet (n) will open, and Piston(d), now pressurized, will open Outlet (e).
The air supplied by the compressor willnow be emitted via Chamber A, Duct Cand Vent 3. Piston (d) also acts as apressure relief valve. In the event of anyexcess pressure, Piston (d) will auto-matically open Outlet (e). If, due to airconsumption, the supply pressure in thesystem falls to a value below cut-in pres-sure, Inlet (n) will close and the pressurefrom Chamber B will be reduced via theunloader valve's vent. Outlet (e) willclose and the drying process will com-mence once again.
Air Dryer 1.
432 420 432 410
12
Air Dryer1.
Air Dryer With Return-FlowLimiting Valve432 413 . . . 0 and 432 415 . . . 0
The single-chamber air dryers from thisseries have an integrated return-flow lim-iting valve which permits the requiredamount of air to be taken from the mainreservoir provided the multiple-circuitprotection valve permits a return flow.Thus no separate regenerating reservoiris required.
Operation:Variant 1 (Control Via Separate Un-loader Valve 432 413 ... 0)
In the delivery phase the compressed airsupplied by the compressor flowsthrough Port 1, opens the check valve (i)and flows into Chamber A. Due to thedrop in temperature, condensation watercollects there which reaches the outlet(e) through Duct C.
The air is dried as described under 432420. At the same time, dried air alsoflows into Chamber E, pressurizing dia-phragm (o). This arches towards theright, releasing the passage betweenChambers E and G via Throttling Port (s).The air supply also reaches Chamber Hvia Filter (l), pressurizing Valve (q). Once
the force of the pressure spring, presetby means of Screw (r), has been over-come, Valve (q) is lifted. The air supplywill now reach Chamber F, acting on theother side of the diaphragm (o) with aslightly lower pressure in keeping withthe retention of Valve (q).
When the cut-off pressure within the sys-tem has been reached, Chamber B ispressurized by the unloader via Port 4.The piston (d) moves downwards andopens the outlet (e). The check valve (i)closes the passage to Port 1 and the airfrom Chamber A flows through Duct Cand is emitted to atmosphere at the outlet(e).
Due to the drop in pressure in ChamberG, the check valve (c) closes. The air tobe regenerated is now taken from the airreservoirs, which is why a multiple-circuitprotection valve must permit its returnflow. The air supply at Port 21 flowsthrough Chamber E, the throttling port (s)where it expands, on into Chamber Gand thus to the underside of the granu-late cartridge (b).
As it passes through the granulate car-tridge (b) in an upward direction, the hu-midity on the surface of the granulate (a)is taken up by the air and emitted to at-mosphere at Vent 3 after passing Duct Cand the opened outlet (e). The return flowis completed when the pressure on the
left of the diaphragm (q) has been re-duced to a point where it reaches its clos-ing position.
When the cut-in pressure at the unloaderis reached, the pressure in Chamber B isreduced once again. The outlet (e) clos-es and the drying process starts again asdescribed above. Outlet 31 also has asafety valve for the pressure side.
Variant 2 (Control Via Integral Unload-er Valve 432 415 ... 0)
In this variant, the cut-off pressure reach-es Chamber J via the connecting holeinto Chamber J and acts on the dia-phragm (m). After the spring force hasbeen overcome, the inlet (n) opens andthe piston (d) which is now pressurizedopens the outlet (e).
The air delivered by the compressor nowflows through Chamber A, Duct C and isemitted to atmosphere at Vent 3. The pis-ton (d) at the same time acts as a popvalve. When the pressure is excessive,the piston (d) automatically opens theoutlet (e).
If air consumption causes the supplypressure within the system to fall belowthe cut-in pressure, the inlet (n) closesand the pressure from Chamber B is re-duced through the vent of the unloadervalve. The outlet (e) closes and the dry-ing process begins again.
432 413 432 415
13
Twin Chamber Air Dryer432 431 . . . 0 and 432 432 . . . 0
Operation:a) Control without Integral Un-
loader ValveThe compressed air supplied by thecompressor flows to Bore E via Port 1.Due to a reduction in temperature, con-densate may form at Bore E, reachingIdling Control Valve (m) via Bore L. FromBore E, the compressed air will passValve (k), enter Chamber B, and reachthe upper side of Desiccant Cartridge (c)via Fine Filter (e) integrated into the car-tridge, and via Annulus A.
Through Sieve Plate (a), the pre-cleanedcompressed air will pass upwardsthrough Granulate (b) sewn into a filterbag in Cartridge (c), reaching Bore G viaSieve Plate (d) and Check Valve (f).
As the air passes through Granulate (b),the inherent moisture is retained by theextremely porous granulate. From BoreG, the compressed air reaches the airreservoirs through Check Valve (g) andvia Port 2.
Through the throttling port of Valves (fand p) designed according to the sweptvolume of the compressor used, part ofthe dried compressed air from Bore Gwill reach the underside of Cartridge (s),passing Granulate (r) in an upward direc-tion (backflush). In this process, themoisture adhering to the fine ducts of theextremely porous Granulate (r) is takenup by the dried air and reaches Vent 3via Annulus K, Chamber H and past theopen rear side of Valve (o).
The additional Charging Valve (h) en-sures that Control Valves (k and o) donot switch over when the system is filledinitially. Valve (h) will not open until asupply pressure of > 5 bar has beenreached at Port 2, permitting com-pressed air to reach Chamber C. If thetimeswitch element integrated in the so-lenoid valve then opens the current sup-ply to Trip Coil (j), Armature (i) will beattracted. Compressed air from Cham-ber C will now flow into Chamber D and,via Bore F, into Chamber M, moving thecontrol valves against the spring forceinto their end positions on the left.
The passage from Bore E to Chamber Bis closed. The compressed air present inChamber B will now be emitted at Port 3
after passing by the open rear side ofControl Valve (k) and going through BoreN. Check Valve (g) will close and thepressure in the system continues to beensured. As a consequence of the pres-sure reduction in Chamber B, CheckValve (f) will also close.
The compressed air supplied by thecompressor will now flow from Bore Ethrough Chamber H, Annulus K andthrough Granulate (r) of Cartridge (s).The drying process of the compressedair is as described before. After Valve (p)and Check Valve (g) have opened, thedried air reaches the reservoirs via Port2. Through the throttling port of Valve (f),dried air reaches the underside of Gran-ulate (b), causing a back-flushing proc-ess to take place here, too.
After approx. 1 minute, the time-switchelement will break the current supply tothe trip coil. Armature (i) will close thepassage from Chanber C, opening thevent, thus reducing the pressure inChambers D and M. Through the springforce and the pressure in Bore G, thecontrol valves are returned to their endpositions on the right. Control Valve (o)will close the passage to Chamber H,and Control Valve (k) will open the pas-
Air Dryer 1.
432 431
14
Air Dryer1.
sage to Chamber B. The compressed airsupplied by the compressor is now againfed into Granulate (b), and the dryingprocess will commence as described be-fore, with alternating cartridges continu-ing to be used at one-minute intervals.
When the unloader valve switches toidling once the input cut-out pressure hasbeen reached, pressure is being fed in atPort 4, pressurizing, and moving down-wards, Piston (m), opening the idlingcontrol valve. Any condensate and impu-rities will be emitted together with the airsupplied in the idling phase via Vent 3.When the unloader valve switches toload, Port 4 is vented and the idling con-trol valve closes the passage to Vent 3.
Any malfunction due to icing in extremeconditions in the area of Piston (e) canbe prevented by fitting a Heating Car-tridge (g) which will switch on at temper-atures below 6°C and switch off againwhen the temperature reaches approx.30°C.
b) Control Via Integral UnloaderValve
The air is dried as described under a).The pressure building up at Port 2 whenthe system is being filled is also present
in Chamber P, pressurizing the under-side of Diaphragm (t). As soon as theforce resulting therefrom is larger thanthe force of Pressure Spring (n), Dia-phragm (t) will arch, taking with it Piston(q). This opens Inlet (u), and Piston (m),now pressurized, is moved downward,opening the idling control valve. Any con-densate and impurities will be emitted to-gether with the air supplied in the idlingphase via Vent 3. The compressor willcontinue to run idle until the pressurewithin the system has fallen to a valuebelow the unloader valve's cut-in pres-sure. The pressure in Chamber P belowDiaphragm (t) will fall simultaneously.Pressure Spring (n) will move Piston (q)and Diaphragm (t) back to their originalpositions. Outlet (u) will close, and thepressure from Chamber O will be re-duced via the vent of the unloader valve.The idling control valve with Piston (m)will close once again. The compressedair will now again flow into Bore E andreach the air reservoirs via Port 2 afterbeing dried in Desiccant Containers (b orr). The system is subsequently filledonce again up to the cut-out pressure ofthe unloader valve.
Application:Depending on the respective application,WABCO provides Single and TwinChamber Air Dryers.
The decision of whether to use a Singleor a Twin Chamber Air Dryer will dependon the compressor's swept volume andon its duty cycle.
Single Chamber Air Dryerscan normally be used for applications upto a swept volume of � 500 litres/minuteand a duty cycle of up to � 50%. Any de-viations of these standard values shouldbe tested in road-test runs.
Twin Chamber Air Drierscover the area > 500 litres/minute and >50% up to 100% duty cycle. Swept vol-umes in excess of 1000 litres/ minuteshould be tested in road-test runs
432 432
15
Purpose:To automatically control the operatingpressure in an air braking system and toprotect its pipes and valves from contam-ination. Depending on the variant used, italso serves to control a downstream anti-freeze pump or single chamber air dryer.
Operation:a) UnloaderThe compressed air supplied by thecompressor flows via Port 1 and Filter (g)to Chamber B. When Check Valve (e)has opened, it flows through the lineleading from Port 21 to the air reservoirsand to Chamber E. Port 22 is intendedfor controlling a downstream anti-freezepump.
Pressure builds up in Chamber E, actingthe underside of Diaphragm (c). As soonas that pressure is greater than the forceof Compression Spring (b), preset bymeans of Screw (a), diaphragm (c) willarch upward, taking with it Piston (m).Outlet (l) closes and Inlet (d) opens, per-mitting the compressed air to pass fromChamber E to Chamber C, forcing Piston(k) downwards against the force of Com-pression Spring (h). Outlet (i) opens andthe compressed air supplied by the com-pressor is released to atmosphere viaExhaust 3. The fall in pressure in Cham-
ber B closes Check Valve (e), thus se-curing the pressure in the system.
The compressor will now continue to idleuntil the pressure within the system fallsbelow the Unloader's cut-in pressure.The pressure in Chamber E below Dia-phragm (c) continues to fall. This causesthe force of Compression Spring (b) topush the diaphragm, together with Piston(m), downwards. Inlet (d) closes, Outlet(l) opens and the air from Chamber C isreleased to atmosphere at Exhaust 3 af-ter passing Chamber F and a connectinghole. Compression Spring (h) forces upPiston (k) and outlet (i) is closed. The airsupplied by the compressor now flowsinto Chamber B, passing Filter (g), andopens Check Valve (e). The system isonce again being filled until the Unload-er's cut-off pressure has been reached.
b) Unloader with Pilot Connec-tion 4 and Port 23
This type of Unloader differs from thetype described under a) merely in theway the cut-off pressure is controlled.The cut-off pressure is not taken from in-side the unloader but from the supply linedownstream from the air dryer. The pas-sage from Chamber B to Chamber E isclosed, and there is no Check Valve (e).Via Port 4 and Chamber A, the air from
the reservoir flows to Chamber E, actingon Diaphragm (c). After that it continuesto operate as described under a). Thepassage between Chambers C and D isopen, permitting pilot pressure fromChamber C to be taken at Port 23 to ac-tuate the single chamber air dryer.
c) Tyre inflation connectionAfter removing the protective cap, thetyre inflation hose is fastened by meansof a union nut moving Pin (f). The pas-sage between Chamber B and Port 21 isclosed. The air supplied by the compres-sor now flows from Chamber B to the tyreinflation hose, passing Pin (f). In theevent of the pressure in the system ex-ceeding 12+2 bar or 20 bar respective-ly during this process, Piston (k) which isdesigned to act as a safety valve willopen Outlet (i) and the pressure is re-leased to atmosphere via Exhaust 3.
Before using the tyre inflation facility, thereservoir pressure must be reduced to avalue below the Unloader's cut-in pres-sure since no air can be extracted whilstthe compressor is running idle
12–
Unloader 1.Combined Unloader975 303 . . . 0
16
Safety Valves1.
Purpose:To limit the pressure within a pneumaticsystem to the permissible maximum.
Operation:The compressed air flows through Port 1and beneath the disk valve (c). When theforce resulting from pressure x surfaceexceeds the preset force of the pressurespring (a), the disk valve (c) is forced up-wards with the piston (b). The excesspressure escapes to atmosphere
through Vent 3 until the force of thespring is greater once again and the diskvalve (c) closes.
The function of the safety valve can bechecked by raising the piston (b).
Safety Valves434 6 . . . . . 0 and934 6 . . . . . 0
434 608 ... 0 934 601 ... 0
434 612 ... 0
17
Purpose:To automatically inject anti-freeze fluidinto the braking system to prevent anymoisture present in pipes and its down-stream components to freeze.
Operation:Depending on the type of anti-freezepump used, it can be fitted downstreamor upstream of the unloader.
Whilst in the anti-freeze pump which isfitted upstream of the unloader the pilotpulse is taken directly from the feed linevia an internal hole as the unloaderchanges from the idle to the load cycle,this pilot pulse has to be taken from aseparate line if the anti-freeze pump is fit-ted downstream of the unloader.
In either case, however, anti-freeze fluidis only injected into the system once theunloader has switched the compressorover to its load cycle, i.e. to supplyingcompressed air into the system.
1. Without a separate pilot con-nection (Fig. 1)
The compressed air supplied by thecompressor flows through the anti-freezepump from Port 1 to Port 2 (Hole J). Thepressure thus building up via Hole (H) inChamber (F) forces Piston (E) to the left.No anti-freeze fluid can reach Chambers(C) or (R) as Hole (K) is closed. The fluidpresent in Chamber (R) is displaced bythe further movement of Piston (E). Itpasses Valve Seat (N), reaching Hole (J)and is dispersed in the braking system bythe passing stream of air.
Once the operating pressure has beenreached in the reservoir, the unloaderswitches the compressor to idle. Thepressure drops in Hole (J) and thus Hole(H) and Chamber (F). CompressionSpring (G) returns Piston (E) to its origi-nal position. Through the re-opened Hole(K), more anti-freeze fluid flows from itsreservoir to Chamber (R).
These processes are repeated everytime the unloader actuates the compres-sor.
2. With a separate pilot connec-tion (Fig. 2)
This operates similarly to the processesdescribed under 1. above. With this vari-ant, the actuating pressure is suppliedvia Port 4 from a separate component,e.g. from the unloader.
Operation and Maintenance:At temperatures below +5°C, the pumpneeds to be activated by turning Lever(B) to Position I. The level of anti-freezefluid must be checked daily.
As temperatures rise above +5°C, thepump can be deactivated by turning Le-ver (B) to Position 0.
During the warm season, the fluid reser-voir does not need to be filled. The posi-tion of Lever (B) is immaterial.
The anti-freeze pump does not requireany special maintenance.
Anti-Freeze Pump 1.Anti-Freeze Pump 932 002 . . . 0
Fig. 1
Fig. 2
18
Purpose:To retain a safe working pressure in theintact circuits of a triple circuit brake sys-tem when one circuit has failed.
Design:Type I With all brake circuits intact valves (c andj) are always kept closed, except duringthe charging operation, by compressionspring acting in the closing direction.
Type II By means of the springs acting under thevalves (c and j) these valves remain openabove a preset opening pressure. In theevent of a slight pressure drop in circuits1 or 2 crossflow from the circuit with thehighest pressure, into the other circuitstakes place. This reduces the frequencyof operation of the unloader.
Operation:Compressed air, passing from the un-loader valve through port 1 into the tripleprotection valve, opens the valves (c and
j) after the preset opening pressure (pro-tection pressure) has been reached, rais-ing the diaphragms (b and k) against theaction of the pressure springs (a and l).The compressed air then flows throughports 21 and 22 into the air reservoirs ofcircuits 1 and 2. It also passes into cham-ber (A) after the non-return valves (d andh) have opened, opens valve (e) andflows through port 23 into circuit 3. Fromcircuit 3 the auxiliary and parking brakeequipment of both the motor vehicle andthe trailer are supplied with air.
If for example circuit 1 fails because of aleak, the compressed air still being sup-plied from the unloader, first passes intothe leaking circuit. But as soon as a pres-sure drop occurs in circuits 2 or 3 afterapplication of the brakes, valve (j) closesbecause of the pressure spring (l) andthe intact circuit under load, is refilled un-til the opening pressure of the valve (j) isreached. This refilling can occur becausethe pressure remaining in the intact cir-cuits after any application of the brakes
exerts a counter-force on pressure spring(a or g) through diaphragm (b or f). Thusvalve (c or e as the case may be) can stillopen even though the opening pressurefor valve (j) has not yet been reached.Pressure protection for circuits I and IIIworks in exactly the same way in theevent of failure of circuit II.
In the event of failure of the auxiliarybrake circuit, a crossflow of air from thereservoirs of circuits 1 and 2 into circuit 3occurs until valve (e) can no longer bekept open by the falling crossflow pres-sure, and it closes when the preset open-ing pressure is reached. The pressuresin the two main brake circuits remainsafeguarded to the level of the openingpressure for the defective circuit 3.
In the event of failure of circuit 1 or 2 be-low the opening pressure of the valves (cor j respectively), the non-return valves(d and h) protect the intact circuit from thefaiIed circuit.
Multi-Circuit Protection Valves1.
Type I
Type II
Three-Circuit Protection Valve934 701 . . . 0
19
Four-Circuit Protection Valves934 702 . . . 0 934 713 . . . 0 / 934 714 . . . 0
Purpose:Retention of pressure in the intact brak-ing circuits in case of failure of one ormore circuits in a four-circuit air-brakingsystem.
Operation: Depending on the variant used, the fourcircuits are connected in parallel and allfour circuits are filled equally, or Circuits3 and 4 are secondary to Circuits 1 and2. The quadruple-circuit protection valvemay, depending on the variant, have by-pass holes in all circuits which ensurethat the braking system is filled from 0bar should one circuit fail.
Compressed air flows from the unloadervalve through port 1 into the protectionvalve and through by-pass bores (a, b, c,and d). It continues through check valves(h, j, q and r) into the four circuits of the
system. Simultaneously, pressure buildsup below valves (g, k, p and s), openingthe valves after reaching the set openingpressure (protection pressure). Also, dia-phragms (f, l, o and t) are raised againstthe force of compression springs (e, m, nand u). Compressed air then flowsthrough ports 21 and 22, to circuit 1 and2 air reservoirs of the service brake sys-tem, and through ports 23 and 24 into cir-cuits 3 and 4. Circuit 3 suppliescompressed air to the emergency andparking brake system of the truck and tothe trailer supply line; circuit 4 suppliesthe auxiliary systems.
If one of the service brake circuits (e.g.circuit 1) fails, air flows from the otherthree circuits into the failed circuit untilthe dynamic valve closing pressure isreached. The force of compressionsprings (e, m, n and u) causes valves (g,k, p and s) to close. If air is consumed incircuits 2, 3, or 4, refilling will occur to thelevel of the set opening pressure of thefailed circuit. Pressure protection of theintact circuits takes place in the sameway if another circuit fails.
If one circuit (e.g. circuit 1) fails, and inaddition, for any reason the pressuredrops to zero bar within the intact cir-cuits, then, when the brake system refills,compressed air flows initially through by-pass bores (a, b, c and d) into all four cir-cuits. The resulting pressure build-up be-low the diaphragms ( f, l and o) of theintact circuits decreases the openingpressure of valves (g, k and p). Furtherpressure increase in port 1 causesvalves (g, k and p) to open. Intact circuits2, 3 and 4 are refilled to the level of theset opening pressure of failed circuit 1and are protected at that level.
Multi-Circuit Protection Valves 1.
934 702
934 713
20
APU - Air Processing Unit1.
APU - Air Processing Unit 932 500 . . . 0
Description:The APU (Air Processing Unit) is multi-functional, i. e. it is a combination of sev-eral types of equipment. It includes an airdryer with an unloader valve, with or with-out heating, depending on the variant, asafety valve and a tyre inflation connec-tor. A multiple-circuit protection valvewith one or two integrated pressure limit-ed valves and two integrated checkvalves is flanged to the air dryer.
Some versions also have a double pres-sure sensor mounted on the multiple-cir-cuit protection valve for measuring thesupply pressures in the service brakingcircuits.
Purpose:The air dryer is used to dry and cleansethe compressed air delivered by the com-pressor, and to control the supply pres-sure. The flanged multiple-circuitprotection valve is used to limit and guardthe pressure in multiple-circuit brakingsystems.
Operation:The compressed air delivered by thecompressor enters at Port 11 and passes
a filter before reaching the granulate car-tridge. As it flows through the granulate,the air is filtered and dried (please refer toAir Dryer 432 410 ... 0 on Page 11). Thedried air then flows through Port 21 toSupply Port 1 of the flanged multiple-cir-cuit protection valve. When the level ofsupply pressure has been reached, theintegrated unloader valve actuates theidle valve and the compressor now deliv-ers to atmosphere. In the idle phase, thegranulate is regenerated in the returnflow via Port 22 with dried and non-com-pressed air.
The air dryer includes a safety valvewhich opens if the pressure becomes ex-cessive. To prevent functional defects ofthe idle valve in winter, a heating systemhas been integrated. The tyre inflationconnector or Port 12 can be used to fillthe system externally (workshop). The airreservoirs for air suspension are con-nected to Port 24.
In a first step, the pressure at Supply Port1 (10 ± 0.2 bar) of the multiple-circuit pro-tection valve is reduced to the level re-quired for the service braking systems,and in a second step (8.5 bar) to thelevel required for the trailer’s braking sys-tem.
In the event of one circuit failing, the
pressure in the other circuits will initiallyfall to the dynamic closing pressure (dueto the trailer) but will then rise again untilit reaches the opening pressure (9.0bar Circuits 1 + 2 and 7.5 bar Cir-cuits 3 + 4) of the defective circuit (= se-cured pressure). This requires thecompressor to be running and to delivermore compressed air. If this pressure isexceeded, the air delivered will escapeinto the defective circuit and thus beevacuated to atmosphere.
An electronic pressure sensor unit per-mits the continuous display of the pres-sures in the service braking circuits. Inaddition, Circuits 3 and 4 have outputs(25 and 26) secured by one check valveeach.
When pressurizing the braking systemstarting at 0 bar, the service braking cir-cuits (1 and 2) are filled first in keepingwith EC guideline 71/320/EEC.
00 4,–
00 3,–0
0 3,–
21
Air Reservoir 1.
Purpose:Storage of the compressed air deliveredfrom the compressor.
Construction:The reservoir consists of the cylindricalportion in the centre with welded-inarched bases and screw necks for con-necting pipes. The use of high-tensilesteels of even material thickness for allair reservoir sizes permits operatingpressures in excess of 10 bar in air res-ervoirs of volumes below 60 litres.
The reference plate is glued on andmust, in keeping with EN 286: 2, containthe following data: number and date ofthe standard, manufacturer's name, seri-al number, modifications, the manufac-turing date, the licence number, thevolume in litres, permissible operating
pressure, minimum and maximum oper-ating temperatures, the CE symbol if inaccordance with 87/404/EC. The nameplate is covered with a sticker showingthe WABCO part number. In the event ofthe air reservoir having been painted bythe vehicle manufacturer, that stickermust be removed to make the actual ref-erence plate become visible.
The air reservoir should be drained reg-ularly to remove any condensate. It is ad-visable to use drain valves which areavailable for both manual and automaticactuation. Regularly check the mountingon the frame and the clamp clips.
Air Reservoir950 . . . . . . 0
Draining the reservoir with a drain valve
22
Drain Valves1.
Purpose:It prevents the accumulation of water inpipe lines and brake chambers throughautomatically draining the reservoirs.
Operation:Air from the auxiliary port on the unload-er enters the control port 4 and pushesthe piston (a) to its lowest position. Waterfrom the reservoir enters port 1 andpasses into chamber (A) via the undercutdiameter on piston (a).
Water in the control line passes intochamber (A) via the small hole in the pis-ton (a).
As the unloader cuts-out, the pressure inthe control line falls to zero, and the pres-sure in the reservoir pushes the piston(a) to its uppermost position, and the wa-ter is ejected via the undercut diameter(b).
The O-ring check valve covering thesmall hole in piston (a) prevents waterand reservoir air in chamber (A) from en-tering the control line - (which might oc-cur during that last few revolutions of thecompressor when the vehicle engine isswitched off, if it were not for the O-ring).
Automatic Drain Valve434 300 . . . 0
Purpose:To drain condensation water from the airreservoir and, if necessary, to exhaustthe compressed air lines and reservoirs.
Operation:Valve (b) is held closed by spring (a) and
by pressure in the reservoir. Pulling orpushing actuating pin (c) in a lateral di-rection opens tilting valve (b). This per-mits both compressed air andcondensation water to escape from thereservoir. On releasing actuating pin (c),valve (b) closes
Drain Valve934 300 . . . 0
23
Drain Valve And Air Pressure Gauges 1.
Purpose:Protection of the compressed-air equip-ment from ingress of condensate bymeans of automatic draining of the airreservoir.
Operation:When the air reservoir is filled, com-pressed air passes through filter (a ) inchamber (B) on to the valve diaphragm(c). This lifts off the inlet (b) on its outerperiphery. Compressed air flows togeth-er with accumulated condensate, if any,out of the air reservoir into chamber (A),where the condensate accumulatesabove the outlet (d). After pressure equi-librium is established between the twochambers the valve diaphragm (c) clos-es the inlet (b).
If, because of a braking action, for exam-ple, the pressure in the air reservoir falls,the pressure in the chamber (B) is re-duced, while in chamber (A) the full pres-sure is at first maintained. The higherpressure in chamber (A) acts from belowon the insert (c) and lifts it off the outlet(d). The condensate is forced out by theair cushion in chamber (A). When thepressure in chamber (A) has fallen farenough to establish a pressure equilibri-um between chamber (B) and (A) again,the insert (c) closes the outlet (d).
To check the function of the drain valvethe outlet can be opened manually bypressing inwards the pin (e) seated in theoutlet.
Automatic Drain Valve934 301 . . . 0
Purpose:Air pressure gauges are used to monitorthe pressure in air reservoirs and brakelines.
Operation:In the single air pressure gauge 453 002,the pressure from the reservoir stretchesthe tube spring which, via a lever andrack, moves the pointer which is mount-ed on a pivot shaft.In the case of a drop in pressure thepointer is returned to the reading of re-
maining pressure by means of a torsionspring.
In the double air pressure gauge 453197, a further red pointer indicates thepressure of air entering the brake cham-bers when brakes are applied. Whenbrakes are released, a torsion spring re-turns this red pointer to the zero position.Reservoir and service pressure readingsare divided into 0 to 10 and 0 to 25 barsrespectively.
Air Pressure Gauges 453 . . . . . . 0
453 002 453 197
24
Check Valves1.
Purpose:To protect the pressurized lines againstunintentional venting.
Operation:Air can only pass in the direction indicat-ed by the arrow. Return flow of the air isprevented by the check valve closing the
inlet in the event of a drop in pressure inthe supply line.
When the pressure rises in the supplyline, the springloaded check valve againopens the passage which results in anequalization of pressure.
Check Valve 434 01. . . . 0
Check-Choke Valve434 015 . . . 0
Purpose:To make sure that the pressure in airreservoirs is not unintentionally de-creased.
Operation:The compressed air from the feed pipeopens Valve (a) and reaches the air res-ervoir provided its pressure is higherthan that within the reservoir. Valve (a)will remain open until the pressures in
the feed pipe and the reservoir areequal.Valve (a) prevents the air from returningfrom the reservoir as, when the pressurein the feed pipe is reduced, the valve it isclosed by Compression Spring (b) andthe higher reservoir pressure.
Air can pass through the check valveonly in the direction from the feed pipetowards the reservoir.
Purpose:To restrict the air flow, optionally whenthe connected line is pressurized or de-pressurized.
Operation:As the air enters in the direction indicat-ed by the arrow, the check valve (a) fit-ted in the housing is raised off its seatand the connected pipe is pressurizedwith no restriction. When the feed pipe ispressurized, the check valve closes and
Port 2 is vented through the throttlingport (b). The cross-section of the throttlecan be adjusted using the adjusterscrew (c). Turning it clockwise will re-duce the cross-section, thus retardingthe venting process, and turning it anti-clockwise will increase the cross-sec-tion.By connecting the air-supply against thedirection indicated by the arrow, pressu-rizing can be throttled, and venting canbe unrestricted.
Check Valve 434 021 . . . 0
unrestricted in direction of air flow
434 019
434 014
direction of air flow
25
Charging Valve 1.
Purpose:Charging Valve with return flow The passing of compressed air to secondair brake reservoir only when the ratedpressure for the system in the first reser-voir has been reached. If the pressure inthe first reservoir falls below that of thesecond reservoir there is a feedbacksupply of air from the second reservoir.
Charging Valve without return flowThe passing of compressed air to auxilia-ry equipment (e. g. door actuation, auxil-iary and parking braking systems, servoclutch, etc.) only when the rated pressurefor the braking system has been reachedin every air reservoir.
Charging Valve with limited returnflow The passing of compressed air to otherconsumers (e. g. auxiliary and parkingbraking systems) only when the ratedpressure for the braking system hasbeen reached in all reservoirs. Also theprotection of pressure for the motor vehi-
cle in the event of the trailer's supply linefailing.
If the pressure in the air reservoirs of theservice braking system drops, part of thecompressed air will return until the clos-ing pressure (which is dependent on theopening pressure) is reached
Operation:With all charging valves, the compressedair passes in the direction of the arrowinto the housing and through port (g) un-der diaphragm (d) which is pressed intoits seat by adjusting spring (b) and piston(c). When the charging pressure hasbeen reached, the force of the adjustingspring (b) is overcome so that the dia-phragm (d) is lifted from its seat, openingport (e). The air flows directly or afteropening of non-return valve (h) to thereservoirs or consumers in the directionof the arrow.
Charging valves with return flow allowthe compressed air to flow back from the
second reservoir after the opening ofcheck valve (f) if the pressure in the firstreservoir has dropped by more than 0.1bar.
In the case of charging valves without re-turn flow, return flow is not possible sincenon-return valve (h) is kept closed by thehigher pressure in the second reservoir.
Charging valves with limited return flowallow the air to flow back until the closingpressure of diaphragm (d) is reached.When this is reached, adjusting spring(b) presses diaphragm (d) into its seatvia piston (c), thus preventing any furtherpressure compensation in the directionopposite to the direction of the arrow.
The charging pressure can be adjustedon all types by turning adjusting screw(a). Turning clockwise increases charg-ing pressure, turning anti-clockwise hasthe opposite effect.
Charging Valve 434 100 . . . 0
with return flow
without return flow with limited return flow
26
Pressure Limiting Valves 1.
Purpose:To limit the output pressure to a presetvalue.
Operation:The Pressure Limiting Valve is set insuch a way that its output pressure onthe low-pressure side (Port 2) is limited.Spring (a) constantly acts on Pistons (cand d), holding Piston (c) in its upper endposition where it is in contact with Hous-ing (h). Inlet (b) is open. The supply airflows from Port 1 to Chamber C and onto Chamber D, reaching the downstreamcomponents via Port 2.
When the pressure building up in Cham-
ber D exceeds the force of CompressionSpring (a), Pistons (c and d) are forceddownwards. Valve (g) closes Inlet (b)and an end position has been reached.
As air is consumed at the low-pressureside, the pressures at Piston (c) are nolonger balanced. Spring (a) will force Pis-tons (c and d) upwards once again. Inlet(b) opens and more air is supplied untilthe pressure has reached the preset val-ue and the pressures are once again bal-anced.
In the event of the pressure on the low-pressure side exceeding the present val-ue, Piston (c) which is designed as a
safety valve will open Outlet (e). The ex-cess pressure will be released to atmos-phere via Exhaust 3.
If the pressure in Chamber C falls belowthat in Chamber D, Valve (f) will beopened. The compressed air fromChamber D will now return through HoleB to Port 1 until the force of Spring (a) isgreater once more, opening Inlet (b). Thepressures between Ports 2 and 1 are bal-anced.
Please note:The 475 010 ... 0 range of pressure limit-ing valves (see Page 71) is also used onthe motor vehicle.
Pressure Limiting Valve 475 009 . . . 0
Purpose:To limit the output pressure.
Operation:The compressed air from the high-pres-sure side, Port 1, flows through the inlet(e) and Chamber B to the low-pressurePort 2. This also causes the diaphragmpiston (c) to be pressurized through HoleA although this is initially being held in itslower position by the pressure spring (b).
When the pressure in Chamber B reach-es the level set for the low-pressure side,the diaphragm piston (c) overcomes the
force of the pressure spring (b) andmoves upwards, together with thespring-loaded valve (d), closing the inlet(e).When the pressure in Chamber B hasrisen above the preset value, the dia-phragm piston (c) continues to move up-wards and is raised off the valve (d). Theexcess pressure escapes to atmospherethrough the drill hole in the piston rod ofthe diaphragm piston (c) and the ventvalve (a).In the event of any leakage in the low-pressure line, Port 2, causing a loss inpressure, the force acting on the dia-
phragm piston (c) falls and causes it tomove downwards, opening the valve (d).An amount of compressed air equallingthe amount of pressure lost is now fed inthrough the inlet (e). When the pressurein the high-pressure line is reduced, thepressure in Chamber B which is nowhigher will initially open the inlet (e) of thevalve (d). Due to the drop in pressure be-neath the diaphragm piston (c), this pis-ton will move downwards, keeping thevalve (d) open. The pressure in the low-pressure line is reduced by the valveconnected with the high-pressure side.
Pressure Limiting Valve 475 015 . . . 0
27
Brake Valves 1.
Purpose:Sensitive increase and decrease in thepressure of the single-circuit servicebraking system of a motor vehicle.
Operation:When the plunger in the spring plate (a)is actuated, the piston (c) moves down-ward, closing the outlet (d) and openingthe inlet (e). The air supply at Port 11flows through Chamber A and Port 21 tothe downstream braking equipment ofthe service braking circuit.
The pressure building up in Chamber Aacts on the underside of the piston (c).This is forced upwards against the forceof the rubber spring (b) until the force act-ing on both sides of the piston is bal-anced. In this position, both the inlet (e)
and the outlet (d) are closed, and a neu-tral position has been reached.
At full brake application, the piston (c) ismoved to its lower neutral position, andthe inlet (e) remains open.
When the pressure in the service brakingcircuit is to be decreased, this process isreversed and can also be achieved grad-ually. The pressure in Chamber A forcesthe piston (c) upwards. The pressure inthe service braking system is now re-duced partially or fully, depending on theposition of the plunger, through openingthe outlet (f) and Vent 3.
Brake ValveFor Single-Circuit BrakingSystems461 111 ... 0With Treadle461 113 ... 0
461 111
461 113
28
Brake Valves1.
Brake Valve With Treadle461 307... 0
Purpose:Sensitive increase and decrease in thepressure of the twin-circuit service brak-ing system of a motor vehicle.
Operation:When the treadle (r) is pushed down, thegraduating piston (a) moves downwards,closing outlet (p) and opening inlet (o).This causes total or partial increase inthe pressure for the brake cylinders ofthe first circuit and the trailer controlvalve from supply port 11 via port 21, de-pending on the amount of force applied.
In this process, the pressure in ChamberA will initially build up beneath the gradu-ating piston (a) and also, through thehole (n), in Chamber B, acting on the re-lay piston (b) of the second circuit. Therelay piston (b) is forced downwardsagainst the force of the spring (l), takingwith it piston (c). This also causes outlet(j) to be closed and inlet (k) to be opened.Compressed air flows from 12 via Port 22into the brake cylinders of the second cir-cuit which are pressurized according tothe controlling pressure in Chamber B.
Because of the force of the spring (l), thepressure in Chamber C is always slightly
lower than that in Chambers A and B.
The pressure building up in Chamber Aalso acts on the underside of the gradu-ating piston (a) which is thus forced up-wards against the force of the rubberspring (q) until the forces on both sides ofthe piston (a) are balanced. In this posi-tion, inlet (o) and outlet (p) are closed(neutral position).
Similarly, as the pressure is increased inChamber C, acting on the underside ofthe pistons (b) and (c), together with thespring (l), these pistons are forced up-wards until they have also reached theirneutral position, i. e. until inlet (k) andoutlet (j) are closed.
When the brakes are fully actuated, thepiston (a) is moved into its lower neutralposition and inlet (o) remains open. Thefull pressure now present in Chamber Bforces the relay piston (b) into its lowerneutral position, and piston (c) keeps in-let (k) open. The full amount of air supplyflows into both service braking circuits.
When the brakes are released, i. e. thepressure in both circuits is decreased,this process is reversed and can also beachieved gradually. The pressure in bothcircuits is reduced through the releasevalve (h).
In the event of Circuit II failing, Circuit Icontinues to operate as described.Should Circuit I fail, the relay piston (b) isno longer actuated; Circuit II then worksmechanically as follows: When thebrakes are actuated, piston (a) is forceddownward. As soon as it makes contactwith the insert (m) which is firmly con-nected to piston (c), this piston (c) is alsopushed downward in the course of itsdownward stroke; outlet (j) closes and in-let (k) opens. Thus Circuit II continues tobe fully operational even if Circuit I hasfailed since piston (c) now operates as agraduating piston.
Different variants of the brake valve havean additional feature allowing the infinite-ly variable adjustment, within a certainrange, of the predominance of Circuit Iover Circuit II by means of pressure re-tention in Circuit II. For this purpose, theinitial tension of the spring (f) is alteredby means of turning the cap (g). As pis-ton (c) moves downwards, the insert (m)connected to it will first make contact withthe spring-loaded plunger (e) beforeclosing outlet (j) and opening inlet (k).The preset initial spring tension now de-termines which pressure in Chamber Cwill move the piston (c) upward off theplunger (e) to reach its neutral position.
with lever 461 491 . . . 0
29
Brake Valves 1.
461 315 ... 0
461 317 ... 0
Variant 461 315 180 0- integrated noise muffler -
Brake Valve461 315 . . . 0With Treadle461 317 . . . 0
Purpose:Sensitive increase and decrease in thepressure of the twin-circuit service brak-ing system of a motor vehicle. Some variants from the 461 315 ... 0 se-ries have an integrated noise muffler toreduce the space required for installingthe valve.
Operation:When the plunger in the spring plate (a)is actuated, piston (c) moves downward,closing outlet (d) and opening inlet (j).The air supply at Port 11 flows throughChamber A and Port 21 to the down-stream braking equipment of servicebraking circuit I. At the same time, com-pressed air flows via Hole D into Cham-ber B, acting on the upper side of piston(f) which is forced downward, closingoutlet (h) and opening inlet (g). The air
from Port 12 flows through Chamber Cand Port 22 to the downstream brakingequipment of Service Braking Circuit II.
The pressure building up in Chamber Aacts on the underside of piston (c). Thisis forced upwards against the force of therubber spring (b) - in variants 180 againstthe force of the pressure springs - untilthe force acting on both sides of piston(c) is balanced. In this position, inlet (j)and outlet (d) are closed, and a neutralposition has been reached.
Similarly, as the pressure is increased inChamber C, acting on the underside ofpiston (f), forcing it upwards again untilits neutral position has been reached. In-let (g) and outlet (h) are closed.
When the brakes are fully actuated, pis-ton (c) is moved into its lower neutral po-sition and inlet (j) remains open. Thepressure in Chamber B also forces pis-ton (f) into its lower neutral position,keeping inlet (g) open. The full amount ofair supply flows into both service brakingcircuits.
When the pressure in the service brakingcircuit is to be decreased, this process isreversed and can also be achieved grad-ually. The pressure in Chambers A and Cforces the pistons (c and f) upwards. Thepressure in both circuits of the servicebraking system is now reduced partiallyor fully, depending on the position of theplunger, through opening the outlets (dand h) and Vent 3.
In the event of one circuit failing, e. g. Cir-cuit II, Circuit I continues to operate asdescribed. If, however, Circuit I fails, pis-ton (f) is moved downwards by the valvebody (e) when the brakes are actuated.Outlet (h) closes and inlet (g) opens. Aneutral position has been reached, asdescribed above.
30
Brake Valves1.
Purpose:Sensitive increase or decrease in thepressure in the dual-circuit service brak-ing system of the motor vehicle andelectrical actuation of the retarder.
Operation:When the treadle (a) is pushed down,Switch I and subsequently, when themechanical pressure point has beenovercome, Switch II are actuated. Thiscauses the first or second braking stageof the retarder to be activated withoutany compressed air flowing into theservice braking system.
As the treadle (a) is pushed down fur-ther, Switch III is actuated, activating thethird braking stage of the retarder. At thesame time the piston (c) moves down-ward.
The operation of this brake valve is sim-ilar to that of 461 315 (description onPage 29).
When the pressure in the two circuits ofthe service braking system is being de-creased, the switching stages of the re-tarder are deactivated as the treadle (a)moves upwards.
Fig. 2 shows a treadle with a built-inproximity switch which is activated whenthe treadle has moved through approx. 2degrees.
Brake Valve With Electrical Switch Or Sensor461 318 . . . 0
Fig. 2
31
Brake Valves 1.
Purpose:Sensitive actuation of the dual circuittruck during brake application and re-lease service brake system. Automaticcontrol of the front brakes through the in-tegrated auto load proportioning valve.
Operation:Operation of pushrod located in springseat (a) forces piston (c) downward, clos-ing outlet (d) and opening inlet (j). Supplypressure at port 11 flows via chamber Aand port 21 to brake boosters installeddownstream as part of service brake cir-cuit I. At the same time compressed airflows through port E into chamber B, ex-erting pressure against surface x1 of pis-ton (f). This is forced downward, openingoutlet (h) and closing inlet (g). Supplypressure air at port 12 flows via chamberC and port 22 to brake boosters fitteddownstream as part of service brake cir-cuit II.
Actual pressure reaching circuit II (seepressurized air circuit) is dependent onpressure modulated by the automaticload proportioning valve. This reacheschamber D via port 4, exerts pressureagainst surface x2 of piston (f), thus aug-menting the force exerted against the topof piston (f).
The pressure built up in chamber A ex-erts a force against the bottom of piston(c). This is forced upward against thepressure exerted by rubber spring (b) un-til pressure is equalized at both ends ofpiston (c). Both inlet (j) and outlet (d) areclosed in this position. An end position isreached.
Correspondingly, pressure built up inchamber C forces piston (f) to move up-ward again, until here too an end positionis reached. Both inlet (g) and outlet (h)are closed.
When brake is applied fully, piston (c) isforced to its lower end position, while theoutlet (j) remains open at all times. Thesupply pressure air acting on surface x1via port E in chamber B, augmented bythe full brake pressure of the rear axlecircuit, forces piston (f) into its lower endposition. Inlet (g) is opened and the sup-ply pressure air flows unimpeded intoboth service brake circuits.
The two service brake circuits are ex-hausted in reverse sequence. This toocan be carried out in steps. The brakepressure built up in chambers A and Cforces the pistons (c) and (f) upwards.Both service brake circuits are fully or
partially exhausted - depending on push-rod position - via the outlets (d) and (h)as these open, as well as through vent 3.The pressure in chamber D is reducedvia the automatic load proportioningvalve fitted upstream.
If pressure is lost in one circuit, e. g. cir-cuit II, circuit I continues to function in themanner described. If, however, there is aloss of pressure in circuit I, piston (f) isforced downward by valve body (e) whenbrakes are applied. Outlet (h) closes andinlet (g) opens. An end position isreached as described above.
Brake Valve461 319 . . . 0
32
Brake Valves1.
Purpose:Sensitive increase or decrease in thepressure in the dual-circuit service brak-ing system of the motor vehicle andpneumatic control of the retarder via thebuilt-in pressure control valve.
Operation:When the treadle (a) is pushed down, thelever (b) initially moves the valve (g)downwards. Outlet (d) closes and inlet (f)opens. The air supply present at Port 13flows through Chamber A and Port 23 tothe downstream retarder. The pressurebuilding up in Chamber A acts on the pis-ton (e). As soon as the force resultingtherefrom is greater than that of the pres-sure spring (c), the piston (e) is forceddownwards. Inlet (f) closes and a neutralposition has been reached. As the trea-dle (a) is pushed down further, the pres-
sure at Port 12 is increased as a ratio oftreadle travel. At the end of the idle trav-el, the pressure in Chamber A is greaterand the pressure is no longer increasedat Port 23 when the service braking sys-tem of the motor vehicle becomes oper-ative.
The operation of the brake valve is simi-lar to that of 461 315 (description onPage 29).
When the pressure in the two circuits ofthe service braking system has been de-creased, the valve (g) is again pushedupwards during the idle travel of the trea-dle (a). Outlet (d) opens and the com-pressed air from Port 23 is reduced viaVent 3 of the pressure control valve.
Brake Valve461 324 . . . 0
Brake Valve With Lever461 482 . . . 0
33
Single Chamber Brake Actuator 1.
Purpose:Producing the brake force at the wheelbrakes using compressed air. Units areavailable with mechanical or hydraulicoutputs.
Operation:As soon as air enters the actuator, the
force on the piston is transmitted throughthe push rod onto the brake lever (or thehydraulic master cylinder). When thepressure is released, the spring pushesthe piston (or the diaphragm) back to itsrunning condition.
Piston Cylinder421 0. . . . . 0 and 921 00 . . . . 0
Brake Chamber423 00 . . . . 0 and 423 10 . . . . 0
Brake Chamber For Expanding Wedge Brake423 0. . . . . 0 and 423 14 . . . . 0
for Disc Brake
34
Air/Hydraulic Actuators1.
Purpose:Pneumatic actuation of the attached hy-draulic master cylinder in air/hydraulicbraking systems.
Operation:When the service braking system is actu-ated, the compressed air from the brake
valve flows through Port A and intoChamber B. The pressure building upthere forces the piston (a) to the rightagainst the force of the pressure spring(c). Force F, this being pressure timessurface, is being transferred via the pres-sure bar (b) onto the piston of the flangedmaster brake cylinder.
When the braking process is ended, thepressure in Chamber B is reduced by theupstream brake valve. At the same time,the pressure spring (c) returns the piston(a) to its original position.
Piston Type Air/HydraulicActuator421 30 . . . . 0
Air/Hydraulic DiaphragmActuator423 0 . . . . . 0
Purpose:Pneumatic actuation of the attached hy-draulic master cylinder in air/hydraulicbraking systems.
Operation:When the service braking system is actu-ated, the compressed air from the brakevalve flows through Port A and intoChamber B. The pressure building upthere acts on the diaphragm (a) andpushes it, together with the piston (b), tothe right against the force of the pressurespring (d). Force F, this being pressure
times surface, is being transferred via thepressure bar (c) onto the piston of theflanged master brake cylinder.
When the braking process is ended, thepressure in Chamber B is reduced by theupstream brake valve. At the same time,the pressure spring (d) returns both thepiston (b) and the diaphragm (a) to theiroriginal positions.
A filter (e) fitted in front of the air outletholes of the cylinder cover prevents dirtor dust penetrating into the inside of the
cylinder when the piston (b) returns to itsoriginal position.
These diaphragm actuators can have awear and/or stroke indicator fitted for thedriver to see which condition the wheelbrakes are in.
Mechanical wear indicators are designedas drag indicators, i. e. it does not returnautomatically. It is actuated after 50% ofthe total stroke and has markings show-ing the driver the amount of wear on thebrake linings.
35
Tristop ® - Spring Brake Actuator425 3 . . . . . 0 for ExpandingWedge Brakes and925 . . . . . . 0 for Cam Brakes
Purpose:Combined spring brake - diaphragmbrake chambers (Tristop ® Spring BrakeActuators) are used to generate thebrake force for the wheel brakes. Theyconsist of the diaphragm portion for theservice braking system and the spring-loaded portion for the auxiliary and park-ing braking systems.
Operation:a) Service Braking System:When the service braking system is actu-ated, compressed air flows into ChamberA via Port 11, acting on diaphragm (d)and forcing piston (a) to the right againstcompression spring (c). Via piston rod(b), the force generated acts on the slackadjuster and thus on the wheel brake.
When the pressure in Chamber A is re-duced, compression spring (c) movespiston (a) and diaphragm (d) back intotheir original positions. The brake cham-ber of the Tristop ® Spring Brake Actua-tor operates independently from itsspring-loaded portion.
b) Parking Brake:When the parking brake is actuated, thepressure in Chamber B is fully or partiallyreleased via Port 12. In this process, theforce of the relaxing compression spring(f) acts on the wheel brake via piston (e)and pressure rod (b).
The maximum braking force of thespring-loaded portion is achieved whenChamber B is pressureless. Since thisbraking force is achieved exclusively bymechanical means, i. e. by compressionspring (f), the spring-loaded portion maybe used for the parking brake. When thebrake is released, the pressure is onceagain increased in Chamber B via Port12.
c) Mechanical Release Mechanism:For emergencies, the Tristop ® SpringBrake Actuator has a mechanical re-lease mechanism for its spring-loadedportion. Should the pressure at Port 12fall to zero, the hexagon head screw (g)wrench size 24 can be screwed out to re-lease the parking brake.
d) Quick-Release Facility(only 425 ... ... 0)To actuate the quick-release function,the bolt head (h) is hit with a hammer.This causes the balls (i) to be releasedfrom the locking mechanism and thepressure bar (f) is returned by the returnforces of the wheel brake.
After remedying the loss in pressure,Port 12 is pressurized once again. Thereturning piston (e) again prestressesthe compression spring (f). At the sametime, the balls (i) lock back into place.
Tristop ® - Spring Brake Actuator 1.
425 ... ... 0
925 ... ... 0
36
Slack Adjuster1.
Automatic Slack Adjuster433 54 . . . . 0 and 433 57 . . . . 0
Slack Adjuster433 50 . . . . 0
Purpose:Transmission of the brake forces to thewheel brake. Automatic readjustment ofthe brake shaft to compensate for liningwear, making the brake cylinder operateroughly within the same stroke range.
Operation:When the brakes are not actuated, thelower edge of the adjuster plate’s jaw isin contact with the pin (e) acting as afixed point. When the brakes are actuat-ed, the adjuster plate (b) covers the dis-tance between the pin (e) and the upperedge of the jaw.
If lining wear has caused the stroke ofthe brake cylinder to increase, the upper
edge of the adjuster plate’s jaw (b)makes contact with the pin (e) and is heldthere. This causes the coupling (g) con-nected to the adjuster plate (b) to beturned in the winding direction of theclutch spring (c) on the worm shaft (f).When the brakes are released, the SlackAdjuster returns to its original position,with the lower edge of the adjusterplate’s jaw again resting against the pin(e), turning the coupling (g) on the wormshaft (f) against the winding direction ofthe clutch spring (c). This turning motioncauses the clutch spring (c) to be un-wound and to sit firmly against the hole inthe coupling (g) of the adjuster ring (d).The resulting high coefficient of frictiondrives the adjuster ring (d) which inter-
locks with the worm shaft (f). The wormshaft (f) and the worm wheel (h) now turnthe brake shaft in the operating direction,thus achieving the best possible adjust-ment for the wheel brake.
To prevent vibrations from turning thecoupling (g) on the worm shaft (f), it ispushed against the adjuster ring (d) bythe spring (a) and thus held in place.
In addition to the version described here,there is one variant which is actuated inthe opposite direction. In that case, thepin (e) is in contact with the upper edgeof the adjuster plate’s jaw (b). Adjust-ment is effected in the same way.
Purpose:Easy, quick and continuous readjust-ment of the brake shaft to compensatefor lining wear, making the brake cylinderoperate roughly within the same strokerange.
(Particularly important for hard linings orpower brakes, and if brake chambers areused, because of the shorter pistonstroke.)
Operation:For readjustment, a ring spanner isplaced on the hexagon (b) of the SlackAdjuster’s mechanism and moved byturning the worm (a). The brake shaftand thus the brake cam are readjustedvia the worm wheel (d). The ball catch (c)for the hexagon (b) prevents unintention-al adjustment of the Slack Adjuster.
371
Hand Brake Valves 1.
Purpose:Sensitive actuation of the trailer controlvalve in order to prevent jack-knifing ofarticulated vehicles and other tractor-trailer combinations (underrun brake).
Operation:In the driving position, the supply pres-sure at Port 1, supported by the pressurespring (i), keeps the valve (g) closed.When the hand lever (a) is in its neutralposition, the cam (c) transfers no forceonto piston (l). The pressure springs holdthe pistons (k and l) in its upper neutralposition, and Port 2 is connected withExhaust 3.
When the hand lever (a) is actuated, thecam (c) forces piston (l) downwards. Thesprings (d and e) are compressed, alsocausing piston (k) to be displaced. Thevalve seat (h) closes the passage be-tween Chamber A and Exhaust 3, andthe valve (g) is raised of the valve seat(j).
The air supply flows into Chamber A andthrough Port 2 to the downstream trailercontrol valve until a pressure level isreached which is similar to the preten-sion of the springs (d and e). The valve(g) closes the inlet valve seat (j) withoutopening the outlet valve seat (h). A finalposition has been reached.
Any additional change in the position ofthe lever also causes the tension of thesprings to alter and output of a corre-sponding control pressure as a ratio ofthe force applied by the cam (c). Similar-ly it is possible to grade evacuation, ei-ther within the partial braking range or forcomplete evacuation of the pilot lineleading to the trailer control valve.
The Hand Brake Valve can be suppliedwith a feature permitting the hand leverto be locked into various positions. Lock-ing or unlocking of this feature isachieved by pushing a button (b).
Hand Brake Valve961 721 . . . 0
38 1
Hand Brake Valves1.
Hand Brake Valve961 722 2. . 0
Purpose:Sensitive actuation of the auxiliary brak-ing system and the parking brake in com-bination with the spring brake actuator.Control position to check the motor vehi-cle’s parking brake.
Design:The Hand Brake Valve consists of a ba-sic valve for the auxiliary and parkingbraking systems which may, dependingon the variant used, also have a safetycircuit valve (emergency release valve)and/or a test valve.
Hand Brake Valve961 722 1. . 0
Purpose:Sensitive actuation of the auxiliary brak-ing system and the parking brake in com-bination with the spring brake actuator.
21
11
3
b
eA
dB
g
FeststellbremsstellungFahrtstellung
a
driving position parking brake position
Version I
22
21
11
3
b
H
cGe
F
A
dB
g
Druckpunkt
Feststellbremsstellung
Prüfstellung
Fahrtstellung
a
driving position parking brake position
test positionworking point
39
Hand Brake Valves 1.
Version I (Variant 252)The test valve combined with the basicvalve can be used to determine whetherthe mechanical forces of the towing vehi-cle’s parking brake are great enough tohold the tractor-trailer combination on acertain uphill or downhill gradient whenthe trailer’s braking system is released.
In the driving position, Chambers A, B, F,G and H are connected and the supplypressure flows to the spring compressionchambers through Port 21 and to thetrailer control valve through Port 22.When the hand lever (a) is actuated, thepressure in Chambers B, F and H is re-duced until it is fully evacuated when theworking point has been reached. Whenthe working point is exceeded, the actu-ating lever reaches an intermediate posi-tion: that of the locked parking brake. Bymoving the lever further to its test posi-tion, the compressed air in Chamber Aflows through Chamber G and openedvalve (c) into Chamber H. By pressuriz-ing Port 22, the relay-emergency valve isactuated which in turn neutralizes the
pneumatic actuation of the brakes in thetrailer which occurred when the auxiliaryor parking brake was actuated. The trac-tor-trailer combination is now held by themechanical forces of the towing vehicle’sspring brake actuators alone. As soon asthe actuating lever (a) is released, it re-turns to its parking brake position inwhich the trailer’s braking system sup-ports the parking brake.
Version II (Variant 262)for power-driven vehicles withpneumatic release deviceAnnex V of the Guideline of the Councilof the European Community defines thatspring braking systems have to have ei-ther a mechanical or a pneumatic auxilia-ry release device. In Version II, the basicvalve has been combined with a safetycircuit valve (emergency release valve)which is intended as a pneumatic auxilia-ry release device.
From separate supply circuits, both Ports11 and 12 are pressurized with com-pressed air. The output pressures 21 and23 reach the spring brake actuatorthrough a 2-way valve. In the event of a
burst pipe causing the pressure to fail an-ywhere in the spring compression circuit,this does not cause uncontrolled emer-gency braking. The emergency releasevalve acts as a pipe rupture safeguardand protects the pressure in the springbrake actuator through the intact 2nd cir-cuit. The driver is alerted to the defect bythe release control lamp but the springbrake actuator remains in its releasedposition.
When the hand lever (a) is turnedthrough approx. 10°, the valve (f) willclose the passage between Chambers Eand D. The compressed air at Port 23 isevacuated to atmosphere throughChamber C and Port 1. Subsequently thenormal, graduated function of the basicvalve begins for braking or parking thevehicle.
Operation:In the driving position, the passage lead-ing from Chamber A to Chamber B isopen and the air at Port 11 flows throughPort 21 into the spring compressionchambers of the Tristop ® Spring BrakeActuators. When the auxiliary brakingsystem is actuated via the hand lever (a),valve (e) closes the passage betweenChambers A and B. The compressed airfrom the spring compression chambersescapes to atmosphere through theopen outlet (d) at Port 3. This causes thepressure in Chamber B to fall and thepiston (b) is forced downwards by thepressure spring (g). As the outlet closes,a final position is reached in all partialbraking positions so that there is alwaysthe right amount of pressure dependingon the desired retardation.
When the hand lever (a) is moved furtherbeyond the working point, a parkingbrake position is reached. Outlet (d) re-mains open and the compressed air isevacuated from the spring compressionchambers.
Within the auxiliary braking range be-tween the driving position to the workingpoint, the hand lever (a) will automatical-ly return to the driving position when re-leased.
23
21
11
3
b
12
Druckpunkt
FeststellbremsstellungFahrtstellung
e
Ad
B
g
Cf
DE
a
Version II
driving position parking brake position
working point
40
Hand Brake Valves1.
Hand Brake Valve961 723 ... 0
Purpose:Actuation of the linkage-free auxiliarybraking system and the parking brake incombination with spring brake actuatorsfor power-driven vehicles which have notrailer attached.
Hand Brake Valve 961 723 1.. 0 is usedtogether with spring brake actuators forlinkage-free auxiliary and parking brak-ing systems. The additional port for actu-ation of the trailer control valve permitsthe transmission of the brake forces tothe trailer. A control position to check themotor vehicle’s parking brake has beenintegrated.
Operation:1. Auxiliary BrakeIn the driving position, valve (c) keepsthe passage between Chambers A and Bopen and the air supply at Port 1 flowsthrough Port 21 and on into the springcompression chambers of the Tristop®Spring Brake Actuators. At the sametime, compressed air flows through thetest valve (b) into Chamber C and on toPort 22, acting on Port 43 of the trailercontrol valve.
When the auxiliary braking system is ac-tuated by means of the hand lever (a),valve (c) closes the passage betweenChambers A and B. The compressed airfrom the spring compression chambersescapes to atmosphere through theopened outlet (d) at Port 3. This alsocauses the pressure in Chamber B todrop, and the piston (e) is forced down-ward by the force of the pressure spring(f). As the outlet closes, a neutral positionis reached in all partial braking positions,thereby ensuring that the spring com-pression chambers always contain theappropriate pressure for the desired re-tardation.
2. Parking PositionWhen the hand lever (a) is moved furtherbeyond the working point, the parkingposition is reached. The outlet (d) re-mains open and the compressed air fromthe spring compression chambers isevacuated completely.
Within the auxiliary braking range, fromthe driving position to the working point,the hand lever (a) will automatically re-turn to its driving position when released.
The test valve combined with the basicvalve can be used to ascertain whetherthe mechanical forces of the towing vehi-cle’s parking braking system are capable
of holding the tractor-trailer combinationon a certain uphill or downhill gradientwhen the trailer’s braking system is notactuated.
3. Test PositionIn the driving position, Chambers A, Band C are connected and the supplypressure flows through Port 21 to thespring compression chambers andthrough Port 22 to the trailer controlvalve. When the hand lever (a) is actuat-ed, the pressure in Chambers B and C isreduced until it is fully evacuated whenthe working point is reached. Whenmoved beyond the working point, thehand lever (a) reaches an intermediateposition: the locked parking position.
When the hand lever (a) is then movedfurther into the test position, the com-pressed air from Chamber A flowsthrough the open valve (b) into ChamberC. By acting on Port 22, the relay-emer-gency valve is actuated which in turnneutralizes the pneumatic actuation ofthe brakes on the trailer caused by theuse of the auxiliary or parking brake. Thetractor-trailer combination is now beingheld by the mechanical forces of the tow-ing vehicle’s spring-brake actuators. Assoon as the hand lever (a) is released, itwill return to its parking brake positionwhich assists the trailer’s parking brake.
961 723 1 . . 0961 723 0 . . 0
41
Solenoid Valves 1.
Purpose:To pressurize an air line when current issupplied to the solenoid.
Operation:The supply line from the air reservoir isconnected to port 1. The armature (b)which forms the valve core keeps inlet(c) closed by the load in pressure spring(d).
When a current reaches solenoid coil (e),armature (b) is lifted, outlet (a) is closed
and inlet (c) is opened. The compressedair from the supply line will now flow fromport 1 to port 2, pressurizing the workingline.
When the current to solenoid coil (e) isinterrupted, pressure spring (d) will re-turn armature (b) to its original position.Inlet (c) is closed, outlet (a) is openedand the working line is exhausted viachamber (A) and exhaust 3.
3/2-Way Solenoid Valvenormally open472 17. . . . 0
Purpose:To vent an air line when current is supp-lied to the solenoid.
Operation:The supply line from the air reservoir isconnected to port 1 and thus air is allo-wed to flow through chamber (A) andport 2 into the working line connected toport 2. The armature (b) which forms thecore of the valve is forced down byspring (d), closing outlet (c).
When a current reaches solenoid coil (e),the armature (b) is lifted, inlet (a) is clo-
sed and outlet (c) is opened. The com-pressed air from the working line will nowescape to atmosphere via port 3 and thedownstream operating cylinder is exhau-sted.
When the current to solenoid coil (e) isinterrupted, pressure spring (d) will re-turn armature (b) to its original position.Outlet (c) is closed and inlet (a) is ope-ned, again allowing air to pass to theworking line via chamber (A) and port 2.
3/2-Way Solenoid Valvenormally closed472 07. . . . 0 and472 17. . . . 0
42 1
Relay Valves1.
Overload Protection Valve473 017 . . . 0 and973 011 20 . 0
Purpose:Prevention of compounding of forces incombined spring brake cylinders andbrake chambers (Tristop brake actua-tors) during simultaneous operation ofthe service and spring brake systems.and thereby protection of the mechanicalactuation equipment against overload.Also rapid supply and evacuation of com-pressed air from spring brake cylinders.
In the 973 011 20. 0 series, the usualconnection (brake valve connected toPort 41 and hand brake valve connectedto Port 42) will cause a reduced pressure(p42 = 8 bar, p2 = 6.5 bar) to reach thespring-loaded portions of the Tristop ®Spring Brake Actuators while the handbrake valve is in the driving position (sa-ving energy in normal driving operation).
Operation:a) Driving position.In the driving position, chamber (A) iscontinuously supplied with compressedair through port 42 from the handbrakevalve. The pressurized piston (a), togeth-er with piston (b), keeps outlet (e) closedand through the depressed valve stem(c) keeps inlet (d) open. Port 2 receivesthe full pressure from the reservoirthrough port 1. The spring brake cylin-ders connected to port 2 are suppliedwith compressed air (reduced if variant973 011 20. 0 is used), and the springbrakes are released.
b) Actuation of the service brake system alone.On actuation of the vehicle brake valve,compressed air flows through port 41 intochamber (B) above piston (b). Becauseof the counter-forces in chambers (A)and (C), the pressure reaching chamber(B) has no effect on the operation of therelay valve. The spring brake section ofthe Tristop actuators continues to be
supplied with compressed air and theyare thus released, while the diaphragmsection supplied with compressed air di-rectly from the tractor brake valve reacts.
c) Actuation of the spring brake system alone.Actuation of the handbrake valve effectspartial or complete evacuation of cham-ber (A). Piston (a), relieved of pressure,is pushed upwards by piston (b), which isexposed to the reservoir pressure inchamber (C). Outlet (e) thereby opens,while inlet (d) is closed by the rising valve(c). This results in evacuation, accordingto the position of the handbrake lever, ofthe spring brake cylinders through port 2,valve stem (c) and exhaust port 3, so thatthe spring brakes are actuated.With partial brake application, outlet (e)closes after the process of evacuationand the pressure equilibrium whichthereby arises in chambers (A) and (C).The relay valve is thus in the neutral po-sition. However, with full brake applica-tion inlet (e) remains open.
473 017 ... 0 973 011 20. 0
431
Relay Valves 1.d) Simultaneous actuation of the service and spring brake systems.1. Service braking with evacuated, i. e.,actuated spring brake cylinders.The spring brake reservoirs are evacuat-ed. If the service brake is also actuated,compressed air flows through port 41into chamber (B) and acts on piston (b),which since chamber (C) is evacuated,moves downwards to close outlet (e) andopens inlet (d) through valve (c). Com-pressed air now flows from 1 throughchamber (C) to 2 and into the springbrake reservoirs. The spring brake isthereby released but only to the extendthat the service brake pressure rises.There is therefore no compounding ofthe two braking forces.
The pressure building up in chamber (C)raises piston (b) as soon as the pressuredelivered at 2 has become greater thanthe pressure present in chamber (B). In-let (d) closes and the relay valve is in theneutral position.
2. Spring braking while service brake isbeing actuated.The service braking system is being ac-tuated within the partial braking range, i.e. Chamber B is pressurized. If now theparking brake is actuated in addition,causing the pressure in Chamber A to bereduced, the supply pressure in Cham-ber C forces the pistons (a and b) up-wards. The valve body following themcloses the inlet (d) and opens the outlet(e). Depending on the level of the servicebraking pressure, compressed air fromthe spring compression chambers will beevacuated to atmosphere through theoutlet (e) and Vent 3 until the pressure inChamber B is greater once again and thepiston (b) closes the outlet (e). A neutralposition has been reached.
When the hand brake valve is actuatedfully, Port 42 is evacuated completely.Since it is impossible for the pressure inChamber C to be lower than that inChamber B, the spring brake is only op-
erated to the extent permitted by the re-spective braking pressure. Compound-ing of the brake forces does not takeplace when the brakes are actuated fully.
On vehicles with an emergency releasefacility, this type of connection may notbe used for Variant 973 011 2.. 0 (differ-ent diameters of pistons a and b). To pre-vent a difference in pressures at thedownstream two-way valve, actuation ofthe hand brake valve must be throughPort 41, and that of the brake valve atPort 42.
When the service brake is released (withparking brake still being actuated),Chamber B is evacuated once again.The pressure in Chamber C is greater,forcing piston (b) upwards. Outlet (e)opens and the spring compressionchambers are connected with Vent 3.
Relay Valve(Plastic Type)973 006 . . . 0
Purpose:Control of the spring-loaded portion onlyin the Tristop ® Spring Brake Actuatorand more rapid increase or decrease inpressure when the hand brake valve isactuated.
Operation:The output pressure from the hand brakevalve flows into Chamber A through Port4, forcing piston (a) into its lower end po-sition, closing the outlet (b) and openingthe inlet (c). The air supply at Port 1 now
flows into Chamber B and through Port 2into the spring-loaded portion of the Tris-top® Spring Brake Actuator.
When the hand brake valve is operated,the pressure in the pilot line is partly orfully evacuated at Port 4. Piston (a) ispushed upward once again by the pres-sure in Chamber B, and the excess pres-sure at Port 2 is evacuated toatmosphere through the outlet (b) andVent 3.
44 1
Relay Valves1.Relay Valve With AdjustablePredominance973 003 000 0
Purpose:To rapidly increase or decrease thepressure of compressed air equipmentand to shorten the response and pres-sure build-up times in air braking sys-tems.
Operation:When the braking system is actuated,compressed air flows through Port 41into Chamber A, forcing the pistons (aand b) downwards. This causes the out-let (c) to be closed and the inlet (e) to beopened. The air supply preset at Port 1flows through Chamber B and on toPort2 to, providing pressure for thedownstream brake cylinders, accordingto the actuating pressure, with a pre-dominance depending on the preset ini-tial tension of the pressure spring (g).
The pressure building up in Chamber Bacts on the undersides of the pistons (aand b). Because of the difference in theeffective areas of piston (a), only piston
(b) is forced upwards against the actuat-ing pressure in Chamber A and the forceof the pressure spring (g). The valve (d)following piston (b) closes the inlet (e)and a neutral position has beenreached.
By turning the adjuster screw (f), the ini-tial tension of the pressure spring (g) canbe changed to achieve a pressure pre-dominance of Ports 2 over Port 41 of upto 1 bar.
When the pressure in the pilot line is par-tially reduced, piston (a) is forced up-wards once again, opening outlet (c),and the excess pressure at Ports 2 isevacuated through Vent 3. If the actuat-ing pressure at Port 41 is fully evacuat-ed, the pressure in Chamber B pushespistons (a and b) to their upper neutralposition and the outlet (c) opens. Thedownstream brake cylinders are evacu-ated fully through Vent 3.
451
Automatic Load Sensing Valves 1.
Purpose:Automatic regulation of the braking forceat the hydraulic wheel cylinders in rela-tion to the load on the vehicle.
Operation:The load sensing valve is fastened to thechassis frame and controlled by a ten-sion spring (c), which is connected to theback axle either directly or by means of alink lever and rod. With increasing load-ing the distance between the axle andthe frame changes. As a result the ten-sion spring (c) is more heavily loadedand the resulting force is carried throughthe lever (b), the bolt (a) as well as thepiston (l) to the load sensing valve.
On applying the service brake systemand with it the hydraulic brake mastercylinder, the hydraulic brake pressurebuilding up in the rear axle circuit passesthrough port 11 into space (A). The pres-sure travels further through the opened
passage (d), into space (D) and port 21to the rear axle wheel cylinders. At thesame time the brake pressure in the frontaxle circuit passes through the port 12into space (B) and moves the piston (h)to the right and end of its stroke againstthe force acting on its rear side in space(A). Should the hydraulic brake pressureinside the rear axle circuit and thereforein space (D) rise above the valve, whichcorresponds with the spring force ap-plied at the lever (b), the pressure inspace (D) moves the piston (l) to theright. The valve (e) closes the passage(d) and a shut-off position is reached.
With a further increase in pressure atport 11, the valve (e) remains closed,and no increase in the output pressuretakes place (cut-off characteristic).
With a reduction in the hydraulic pres-sure at port 11 the higher pressure inspace (D), which acts through the drilling
(C) on the non-return valve (f), movesthis to the left against the force of thespring (g). The brake pressure in the rearaxle circuit now falls through the drilling(C), the by-pass (k) and the port 11. Theforce of the tension spring (c) pressesthe piston (l) back to the left, the valve (e)opens the passage (d) and the brakepressure now passes through the pas-sage (d) to port 11.
Should the front brake circuit fail the hy-draulic brake pressure will only build upon applying the service brake system inspaces (A and D). With it the piston (h) ispressed to the left and end of its stroke.The valve tappet (j) pulls the valve (e) upand the passage (d) remains constantlyopen. The hydraulic brake pressure nowpasses unhindered to the rear axle wheelcylinders.
Automatic Load SensingValve468 402 . . . 0
46 1
Automatic Load Sensing Valves1.
Purpose:Automatic regulation of the braking forceat the hydraulic wheel cylinders in rela-tion to the load on the vehicle.
Operation:The load sensing valve is fastened to thechassis frame and controlled by a ten-sion spring (c) which is connected to theaxle either directly or by means of a linklever and rod. With increasing loadingthe distance between the axle and theframe changes. As a result the tensionspring (c) is more heavily loaded and theresulting force is transmitted through thelever (b). the bolt (a) and the piston (f) tothe brake apportioning valve.
On applying the service brake systemand with it the hydraulic brake mastercylinder the hydraulic brake pressurebuilding up in the rear axle circuit passesthrough port 1 into space (A), the pres-sure passes through the opened valve(d) into space (B) and further throughport 2 to the rear axle wheel cylinders.Should the hydraulic brake pressure in-side the rear axle circuit and therefore inspace (B) rise above the valve, whichcorresponds with the spring force ap-plied at the lever (b), the pressure in
space (B) moves the piston (f) to theright. The valve (d) closes and a shut-offposition is reached.
With a further increase in pressure atport 1, and therefore in space (A) thepiston (f) is again moved to the left. Thevalve (d) open and fluid passes throughport 2 to the wheel cylinders, increasingthe pressure. When the force to the righton piston (f), resulting from the pres-sures in spaces (A and B) again reactsthe valve corresponding to the springforce applied at the lever (b), the valve(d) closes again.
With a reduction in the hydraulic brakepressure at port 1 and with it also inspace (A), the valve (d) is openedthrough the pressure present in space(B). The brake pressure in the rear axlecircuit is now reduced through port 1 andthe previously operated master cylinder.The force of the draw spring (c) transmit-ted by the bolt (a) presses the piston (f)back to the leftward end of its stroke dur-ing a pressure decrease in space (B).The valve (d) rests on the housing (e)and remains open.
Automatic Load SensingValve 468 404 . . . 0
471
Automatic Load Sensing Valves 1.Automatic Relay Load Sensing Valve 475 710 . . . 0
Purpose:To automatically control the brakingforce as a function of the spring deflec-tion and thus of the vehicle load. The in-tegral relay valve ensures rapid supplyand exhaust of the brake actuators.
Operation:The valve is mounted on the vehiclechassis and connected to a fixed point onthe axle by a flexible arm or a linkage.When the vehicle is empty, the distancebetween the axle and the valve is great-est and lever (j) is in its lowest position.As the vehicle is loaded, this distance isreduced and lever (j) moves from its”empty“ position towards its ”fully laden“position. The movement of lever (j) caus-es cam (i) to rotate and to lift valve tappet(h) to a position corresponding to the ve-hicle load.
On application of the brakes, air from thetruck foot-brake valve or relay emergen-cy valve enters chamber (A) via port 4,forcing down piston (b). Outlet (d) isclosed and inlet (m) opened. Com-pressed air at port 4 reaches chamber(C) below diaphragm (e), acting on theeffective surface area of relay piston (f).
At the same time, air flows into chamber(D) via opened valve (a) and passage(E), acting on the upper side of dia-phragm (e). This initial by-pass pressureeliminates any reduction in pilot pressure(up to 1.0 bar max.) in the ”partially lad-en“ condition. As the pilot pressure con-tinues to rise, piston (n) is forced upagainst the load of spring (o), closingvalve (a).
The pressure building up in chamber (C)forces down relay piston (f). Outlet (g)closes and inlet (k) opens. The supplypressure at port 1 now flows into cham-ber (B) via inlet (k) and to the brake actu-ators via ports 2. At the same time,pressure builds up in chamber (B) actingon the underside of relay piston (f). Assoon as this pressure exceeds the pres-sure in chamber (C), relay piston (f)slides down, closing inlet (k).
As piston (b) moves down, diaphragm (e)is forced against vane (I). As soon as theforce in chamber (C) acting on the under-side of the diaphragm is equal to theforce acting in piston (b), the pistonmoves upward. Inlet (m) is closed. A bal-anced position is reached.
The position of valve tappet (h) which iscontrolled by the position of lever (j) de-termines the output pressure. Piston (b)with vane (I) need to cover a certainstroke depending on the position of valvetappet (h) before valve (c) begins to op-erate. This stroke also changes the ef-fective surface area of diaphragm (e). Inthe ”fully laden“ position, the input pres-sure at port 4 is the same as that reach-ing chamber (C). As full pressure isapplied to relay piston (f), it keeps inletvalve (k) open and the brake pressure isnot regulated.
When the pilot pressure at port 4 is re-duced, relay piston (f) is forced up by thepressure in ports 2. Piston (b) is forcedup by the pressure in chamber (C). Out-lets (d and g) open and the compressedair escapes to atmosphere via exhaust 3.
In the event of the linkage breaking, thevalve will automatically move to theemergency control curve of the cam (i)whose output pressure is approximatelyhalf the service braking pressure whenthe vehicle is fully laden.
48 1
Automatic Load Sensing Valves1.
Automatic Load SensingValve 475 711 . . . 0
Purpose:Automatic control of the brake force de-pending on the bellows pressure andthus on the load of the vehicle. The inte-grated relay valve assures quick pressu-rizing and venting of the brake cylinders.
Operation:The load-sensing valve is actuated bythe pressure of both circuits of the air bel-lows from Ports 41 and 42. The pistonvalve (i) pushes the working piston (j)with the radial cam (m) to the left againstthe force of the spring (l). This causes theradial cam (m) to take the valve tappet(h) to the appropriate position for the ve-hicle’s load.
The compressed air output by the brakevalve flows through Port 4 and on intoChamber A, acting on the piston (b). Thisis forced downward, closing the outlet (d)and opening the inlet (q). The com-pressed air from Port 4 flows into Cham-ber C beneath the diaphragm (e), actingon the effective area of the relay piston(f).
At the same time, compressed air flowsthrough the open valve (a) and Duct Einto Chamber D, acting on the upper sideof the diaphragm (e). This pressure pre-dominance causes the reduction in thepartially-laden range to be neutralized at
low actuating pressures (up to 0.8 bar).As the actuating pressure continues torise, the piston (r) is forced upwardsagainst the force of the spring (s) and thevalve (a) closes.
The pressure building up in Chamber Cforces the relay piston (f) downwards.The outlet (g) closes and the inlet (o)opens. The air supply at Port 1 now flowsthrough the inlet (o) into Chamber B andthrough Ports 2 to the downstream com-pressed-air brake cylinders. At the sametime, pressure builds up in Chamber Bwhich acts on the underside of the relaypiston (f). As soon as this pressure ex-ceeds that in Chamber C, the relay pis-ton (f) moves upwards, closing the inlet(o).
As the piston (b) moves downwards, thediaphragm (e) makes contact with thefan-type disk (p), thereby continuouslyincreasing the effective diaphragm area.As soon as the force in Chamber C whichacts on the underside of the diaphragm(e) is equal to the force acting on the pis-ton (b), that piston moves upwards. Inlet(q) is closed and a neutral position hasbeen reached.
The position of the valve tappet (h) whichdepends on the position of the radial cam(m) determines the output control pres-sure. The piston (b) with the fan-type disk(p) must have covered a stroke depend-ing on the position of the valve tappet (h)before the valve (c) begins to act. This
stroke also causes the effective area ofthe diaphragm (e) to be changed. In thefully-laden position, the output pressurefrom Port 4 is passed on into Chamber Cat a ratio of 1:1. The full pressure actingon the relay piston (f) causes the inlet (o)to be kept open and the input controlpressure is not adjusted.
When the actuating pressure at Port 4 isreduced, the pressure in Ports 2 forcesthe relay piston (f) upwards and the pis-ton (b) is forced upwards by the pressurein Chamber C. The outlets (d and g)open and the compressed air is evacuat-ed to atmosphere through Vent 3.
If the pressure in one air bellows fails, theload-sensing valve automatically movesto a position which approximately corre-sponds to half the pressure in the intactactuating circuit. If the pressure drops inboth air bellows, the small pressurespring (k) in the ram cylinder moves theworking piston to the right to the pointwhere the tappet is automatically takenthrough the dip onto the radial cam. Theoutput pressure then roughly corre-sponds to half the service braking pres-sure of the fully laden vehicle.
Test connection 43 allows the load-sens-ing valve to be checked on the vehicle.For this purpose, the piston valve is pres-surized with the preset test pressurewhile the pressure of the air bellows areautomatically separated from the load-sensing valve.
49
Automatic Load Sensing Valves 1.
1
Automatic Load SensingValve 475 720 . . . 0
Purpose:Automatic control of the brake force de-pending on the spring deflection and thuson the load of the vehicle. By the integra-ted relay valve the brake cylinders arequickly pressurized and vented.
Function:The load sensing valve is fixed on the ve-hicle frame and connected via a linkagewith a fixed point on the axle resp. on theknuckle joint. The distance between theaxle and the load sensing valve is thelongest in unladen condition, the lever (j)is in its lowest position. When the vehicleis laden, the distance becomes smallerand the lever (j) is moved from its unlad-en position into full-load direction. Thepin (i) which is turned in the same sensewith lever (j) moves the rod (q) via camsin the bearing cover (p) and thus thevalve tappet (g) into the postion corre-sponding to the load.
The compressed air (control pressure)which is delivered by the brake valveflows via the port 4 into the room A andpressurizes the piston (b). The piston (b)is moved to the left, closes the outlet (d)and opens the inlet (m). The compressedair which is delivered at the port 4 flowsinto the room C left of the diaphragm (e)
and through the channel F into the roomG and pressurizes the active surface ofthe relay piston (f).
At the same time, compressed air flowsvia the open valve (a) and the channel Einto the room D and pressurizes the rightside of the diaphragm (e). This anticipa-tory control of the pressure eliminatesthe reduction ratio in partial laden rangeat small input pressures (up to max. 1,4bar). When the input pressure increasesagain, the piston (n) is moved against theforce of the spring (o), and the valve clos-es.
The pressure which builds-up in room Gmoves the relay piston (f) downwards.The outlet (h) closes and the inlet (k)opens. The supply air at port 1 flows nowvia inlet (k) into room B and reaches viathe ports 2 the subsequent air brake cyl-inders. At the same time, pressure buildsup in room B which acts on the bottomside of the relay piston (f). As soon asthis pressure becomes a bit higher thanthe pressure in room G, the relay piston(f) moves upwards, and the inlet (k) clos-es.
While the piston (b) is moving to the left,the diaphragm (e) touches the washer (l),and thus increases constantly the activesurface of the diaphragm. As soon as theforce which acts in room C on the left
side of the diaphragm is identic to theforce which acts on the piston (b), piston(b) moves to the right. The inlet (m) clos-es and a final position is reached.
The position of the valve tappet (g),which depends on the position of the le-ver (j), is decisive for the active surface ofthe diaphragm and so for the deliveredbrake pressure. The piston (b) with thewasher (l) must make a stroke corre-sponding to the position of valve tappet(g), before the valve (c) starts working.This stroke changes the active surface ofthe diaphragm (e). In full-load positionthe active surfaces of the diaphragm (e)and the piston (b) have identic size. Thusthe pressure delivered at port 4 is deliv-ered in a 1:1 ratio into room C and soalso into room G. As the relay piston (f) ispressurized with full pressure, the relaypart delivers the pressure 1:1. Thatmeans, there is no reduction of the inputbrake pressure.
After the input pressure at port 4 is ex-hausted, the pressure in room C movesthe piston (b) to the right and the pres-sure in the ports 2 moves the relay piston(f) upwards. The outlets (d and h) open,and the compressed air escapes to at-mosphere via exhaust 3.
50
Automatic Load Sensing Valves1.
1
Automatic Load SensingValve 475 721 . . . 0
Purpose:Automatic control of the brake force de-pending on the bellows pressure andthus on the load of the vehicle. The inte-grated relay valve assures quick pressu-rizing and venting of the brake cylinders.
Function:The load sensing valve is controlled bythe pressure of the two circuits of the bel-lows via ports 41 and 42. The control pis-ton (i) which is pressurized by thebellows pressure moves the valve tappet(g) against the force of the spring (j) intothe position corresponding to the load.Thus the average value of the bellowspressures 41 and 42 is effective.
The compressed air delivered from thebrake valve (control pressure) flows viaport 4 into room A and pressurizes piston(b). Piston (b) is moved to the left, closesoutlet (d) and opens inlet (m). The com-pressed air delivered at port 4 flows intoroom C left of the diaphragm (e), as wellas through channel F into room G andpressurizes the active surface of the re-lay piston (f).
At the same time, compressed air flowsvia the open valve (a) and channel E intoroom D and pressurizes the right side ofthe diaphragm (e). This anticipatory con-trol of the pressure eliminates the reduc-
tion in the partial laden range at smallinput pressures (up to max. 1,4 bar).When the input pressure increasesagain, the piston (n) is moved against theforce of the spring (a) and the valve clos-es.
The pressure which builds-up in room Gmoves the relay piston (f) downwards.The outlet (h) closes and the inlet (k)opens. The supply air at port 1 flows nowvia inlet (k) into room B and reaches thesubsequent air brake cylinders via theports 2. At the same time, pressurebuilds up in room B which acts on thebottom side of the relay piston (f). Assoon as this pressure becomes a bithigher than the pressure in room G, therelay piston (f) moves upwards and theinlet (k) closes.
While the piston (b) is moving to the left,the diaphragm (e) touches the washer(l), and thus increases constantly the ac-tive surface of the diaphragm. As soonas the force which acts in room C on theleft side of the diaphragm, is identic tothe force which acts on the piston (b),piston (b) moves to the right. The inlet(m) closes and a final position isreached.
The position of the valve tappet (g),which depends on the position of thecontrol piston (i), is decisive for the activesurface of the diaphragm and thus for thedelivered brake pressure. The piston (b)
with the washer (l) must make a strokewhich corresponds to the position of thevalve tappet (g), before the valve (c)starts working. This stroke changes alsothe active surface of the diaphragm (e).In full-load position the active surfaces ofdiaphragm (e) and piston (b) have thesame size. Thus the pressure deliveredat port 4 is delivered in 1:1 ratio into roomC and so also into room G. As the relaypiston (f) is pressurized with full pres-sure, the relay part delivers the pressure1:1. The delivered brake pressure is notreduced.
After the control pressure at port 4 is ex-hausted, the pressure in room C movesthe piston (b) to the right and the pres-sure in the ports 2 move the relay piston(f) upwards. The outlets (d and h) openand the compressed air escapes to at-mosphere via exhaust 3.
If one bellows pressure fails, the valvemoves automatically into a positionwhich corresponds to approx. half thepressure of the intact control circuit. Ifboth bellows pressures fail, the valvemoves automatically into unladen posi-tion.
The test valve with port 43 makes it pos-sible to check the load-sensing valve inthe vehicle. For this the control circuits41 and 42 are pressurized via the testhose while the bellows pressures areseparated from the valve by connectingthe test hose.
511
Knuckle Joint433 302 . . . 0 and 433 306 . . . 0
Purpose:To prevent damage to the automaticload sensing valve.
Operation:In the event of large axle movements inexcess of the range of movement of theautomatic load sensing valve, arm (e),which is horizontal while at rest, is de-flected about a fixed point in housing (c).Pressure springs (a) and (b) exert pres-sure on ball (d) providing constant ten-sional contact with housing (c) until arm
(e) again returns to its normal horizontalposition where it is again in full contactwith the front face of the housing.
Deformation of the connecting linkage tothe automatic load sensing valve is pre-vented by a ball joint (f) or the rubberthrust member attached to arm (e).
Knuckle Joint 1.
433 306
433 302
52 1
Purpose:To control the braking force at the frontaxle of trucks or truck-tractors in re-sponse to the load-sensing valve on therear axle, as well as to provide for thequick release of air from the brake cham-bers.
Operation:During braking, output pressure from thedual-brake valve passes through port 1to the upper side of the step piston (d),pushing it downward against its stop. As
a result, double valve (a) closes outlet (b)and opens inlet (c), thus permitting inputpressure to flow through ports 2 to thebrake chambers.
Simultaneously, changes in output pres-sure (effected by the load condition of thevehicle) are directed by the load-sensingvalve on the rear axle, thru port 4, ontothe ring surface of step piston (d). Inlet(c) closes whenever the ratio betweenthe input pressures (ports 1 and 4) andoutput pressures (ports 2) is equivalent
to the aspect ratio of step piston (d).
Whenever the control pressures at ports1 and 4 drop, the higher brake chamberpressure raises piston (d) and doublevalve (a). Outlet (b) then opens to a de-gree determined by the control pressure,and a partial or complete the quick re-lease of air from the brake chamber oc-curs via exhaust 3.
Emty / Load Valve and Pressure Reducing Valve1.
Empty / Load Valve 473 300 . . . 0
d
1
2 2
3
c
ba
4
d
1
2 2
3
c
ba
Pressure Reducing Valve473 301 . . . 0
Purpose:To reduce the input pressure at a definedratio and to rapidly reduce the pressureof the downstream components of thebraking system.
Operation:Via Port 1, compressed air flows intoChamber A, forcing differential piston (d)downward against compression spring(a). Outlet valve (b) is closed and inletvalve (c) opened. Via Port 2, the com-
pressed air flows to the downstreamcomponents of the braking system.
At the same time, the pressure buildingup in Chamber B will act on the under-side of piston (d). As soon as the forceson the underside and the smaller uppersurface of differential piston (d) is bal-anced, the piston is raised and inlet valve(c) closed. The ratio of the pressures willthen be equal to the ratio of the two sur-faces of the differential piston.
When the pressure at Port 1 falls, thehigher pressure in Chamber B forces dif-ferential piston (d) upwards. Outlet valve(b) opens, and the pressure for thedownstream components of the brakingsystem will be reduced partially or in full.Compression spring (a) holds the differ-ential piston in its upper final positioneven if there is no pressure acting on it.
53
Empty / Load Valve 1.
Purpose:To control the braking force at the frontaxle by the rear axle load-sensing valve,as weIl as to provide for the quick releaseof air from the brake chambers.
Operation:a) Brakes actuated - partially loadedvehicle:When the service brake system is actuat-ed, the air pressure controlled by the rearaxle ALV is supplied to the brake cham-bers of the rear axle, and is delivered ascontrol pressure to port 4 of the empty/load valve. This control pressure is trans-mitted via bore (E) into chamber (C)where it acts upon the upper surface ofpiston (d) against the force of compres-sion spring (e). At a pressure of 0.5 bar,the piston is lowered to the stopped posi-tion. Spring loaded valve (b), moving inconjunction with piston (d), closes inlet(c) and outlet (f) opens. The control pres-sure also acts in chamber (B) upon thering-shaped area of piston (a).
Simultaneously, the output pressure ofcircuit (II) of the tractor brake valve istransmitted via port 1 to chamber (A) andacts upon the top of piston (a). Piston (a)
is moved down, outlet (f) closes, and inlet(c) opens. The compressed air flows viachamber (D) and port 2 into the front axlebrake chambers.
The built-up pressure in chamber (D)then moves piston (a) upwards. Inlet (c)closes and a neutral position is reached.
b) Brakes actuated - fully loaded vehi-cle:The operation of the empty/load valvewith a fully loaded vehicle is the same aspreviously described. When the tractorbrake valve is actuated, the control pres-sure acts now with full service brakepressure in chambers (A and B) and thepressure reduction is interrupted. The in-put to output pressure ratio through theentire range of brake pressures is in thiscase 1 :1.
When exhausting the brake system,pressure at ports 1 and 4 decreases viathe dual-circuit brake valve. Simultane-ously, the brake pressure in chamber (D)moves piston (a) upwards. Inlet (c) clos-es and outlet (f) opens, and the brakechambers connected to port 2 are ex-hausted via exhaust port 3.
Piston (d) remains in its lower stop posi-tion until pressure at port 4 drops to 0.5bar. With further pressure decrease inchamber (C), compression spring (e)then moves piston (d) upwards. Outlet (f)closes and inlet (c) opens, and the re-maining pressure in port 2 is exhaustedvia port 1.
c) Operation when the rear axle brakecircuit fails:If the rear axle brake circuit fails, port 4and chamber (C), above piston (d), re-main without pressure when the servicebrake system is actuated. The force ofcompression spring (e) keeps piston (d)in its upper stop position. Inlet (c) re-mains constantly open. Compressed airfrom the service brake circuit (II) of thedual-circuit tractor brake valve, flowswithout limitation through the empty/loadvalve to the front axle brake chambers.
Empty / Load Valve473 302 . . . 0
54
Purpose:To control the dual-line trailer brake sys-tem, in conjunction with the dual-circuittractor brake valve and the hand controlvalve for spring brake actuators.
Operation:a) Control from the dual-circuit tractorbrake valveUpon actuation of the tractor brake valve,compressed air flows from service brakecircuit (I), through port 41, into chamber(A) and pushes down pistons (a and i).When piston (i) comes to rest on valve(d), outlet (c) closes and inlet (h) opens,filling chamber (C). Compressed airpasses from chamber (C), throughchamber (B), to port 2 and supplies thetrailer control line in proportion to servicebrake circuit (l) pressure with a gain de-pending upon the pre-set tension ofspring (b).
The built-up pressure in chamber (B)acts upon the underside of pistons (a andi). Due to the different operating surfaceof piston (a), only piston (i) is raisedagainst the control pressure in chamber(A), forcing compression spring (b) up-wards. The sequential action of valve (d)closes inlet (h), and a neutral position isreached. With full brake application,
however, the pressure on the upper sideof piston (i) is predominant and inlet (h)remains open.
The pre-set tension of compressionspring (b) can be changed by turning theadjusting screw (j) until the pre-set pres-sure gain of port 41, in relation to port 2,reaches 1 bar maximum.
Simultaneous to the operations takingplace in port 41, service brake circuit (II)supplies chamber (E), beneath dia-phragm (e), with compressed air throughport 42. However, due to the filling ofchamber (B and D), the pressure abovepiston (g) and diaphragm (e) predomi-nates and the position of piston (g) doesnot change. If service brake circuit (I)fails, port 42 is supplied with compressedair through circuit (II). The pressure inchamber (E), beneath diaphragm (e),moves piston (g) and valve (d) upwards.Piston (i), now in its upper end position,closes outlet (c) and opens inlet (h) sothat the trailer control line receives com-pressed air proportional to the tractorbrake application.
With partial brake application, piston (g),after pressure build-up in chamber (B),moves downwards, inlet (h) closes and a
neutral position is reached. With fullbrake application, the pressure in cham-ber (E) predominates and inlet (h) re-mains open.
When controlled through circuit (II) of theservice brake system, the trailer brakevalve operates without predominance.
b) Control from the hand control valveThe progressive evacuation of the springbrake actuators through the hand controlvalve brings about a correspondingevacuation of chamber (D) through port43. The supply pressure, now predomi-nant in chamber (C), moves piston (g)upwards. The supply of air to port 2 thentakes place in the same way as for thecontrol of chamber (E) in the event of fail-ure of service brake circuit (I).
After completion of the braking action,ports 41 and 42 are exhausted, and port43 is re-pressurized. The pressure inchamber (B) causes pistons (a and i) andpiston (g) to return to their original posi-tions. Outlet (c) opens and the com-pressed air in port 2 is exhaustedthrough the hollow piston body (f) andexhaust port 3 to the outside.
Trailer Control Valves1.Trailer Control Valve with predominance 973 002 . . . 0
55
1.
Purpose:To control the dual line trailer brake sys-tem, in conjunction with the dual circuittractor brake valve and the hand controlvalve for spring brake actuators.
If the trailer control line breaks or is dis-connected, and the tractor brake valve isapplied, the supply of air from the tractorto the trailer is restricted by the 2/2 wayvalve; simultaneously, pressure in thetrailer supply line is exhausted.
Operation:While the air brake system is filling, sup-ply air passes through port 11 into the 2/2 way valve and acts upon piston (l).Piston (l) is moved against the force ofthe spring (n) into its upper position. Sup-ply air passes through chamber (C) andport 12 to the automatic hose coupling.
a) Control from the dual circuit trac-tor brake valve
Trailer Control Valves
Upon actuation of the tractor brake valve,compressed air flows from the servicebrake circuit 1, through port 41, intochambers (A) and (G) and pushes downpistons (c and l). Pistons (c) are pusheddown at the same time. When piston (c)comes to rest on valve (g), outlet (e) clos-es and inlet (f) opens. Compressed airpasses from chamber (C), throughchamber (B), to port 22 and supplies thetrailer control line in proportion to theservice brake circuit 1 pressure.
At the same time as the aforementionedoperations are proceeding, compressedair flows through channel (k) into cham-ber (F) and acts upon the underside ofpiston (l). At a control pressure of ap-proximately 4 bar, the compressed airabove piston (l) predominates, movingthe piston downwards until it stops at thehousing edge (m). This movement is de-signed to keep piston (l) from seizing.
The pressure building up in chamber (B)acts upon the undersides of pistons (c)and moves this upwards against the con-trol pressure acting in chamber (A). Thesequential action of valve (g) closes inlet(f) and a neutral position is reached. Withfull brake application. however, the pres-sure above piston (c) is predominant andinlet (f) remains open.
Simultaneous to the operations takingplace at port 41, service brake circuit 2supplies chamber (E), beneath the dia-phragm (i), with compressed air throughport 42. However, due to the filling ofchambers (B and D), the pressure abovepiston (h) and diaphragm (i) predomi-nates, and the position of piston (h) doesnot change. If service brake circuit 1 fails,port 42 is supplied with compressed airthrough circuit 2. The pressure in cham-ber (E), beneath diaphragm (i), movespiston (h) and valve (g) upwards. Piston(c), now in its upper end position, closesoutlet (e) and opens inlet (f) so that thetrailer control line receives compressedair proportional to the tractor brake appli-cation.
With partial brake application, piston (h),after pressure build up in chamber (B),moves downwards, inlet (f) closes, and aneutral position is reached. With fullbrake application, the pressure in cham-ber (E) predominates and inlet (f) re-mains open.
When controlled through circuit 2 of theservice brake system, the trailer brakevalve operates without gain.
If the trailer control line (connected toport 22) breaks while the service brake
system is actuated, no pressure build upoccurs in chambers (B and F). The con-trol pressure in chamber (G) moves pis-ton (l) downwards, and the flow from port11 to port 12 is partially restricted. At thesame time, pressure in the trailer supplyline (port 12) exhausts through open inlet(f) and through the trailer control line rup-ture, and causes automatic trailer brak-ing.
b) Control from the hand controlvalve
The progressive evacuation of the springbrake actuators through the hand controlvalve brings about a correspondingevacuation of chamber (D) through port43. The supply pressure, now predomi-nant in chamber (C), moves piston (h)upwards. The supply of air to port 22then takes place in the same way as forthe control of chamber (E) in the event offailure of service brake circuit 1.
After completion of the braking action,ports 41 and 42 are exhausted, and port43 is repressurized. The pressure inchamber (B) causes pistons (c and h) toreturn to their original positions. Outlet(e) opens and the compressed air in port22 is exhausted through the hollow pis-ton body (j) and exhaust port 3 to the out-side.
Trailer Control Valve with 2/2 Way Valve and without predominance 973 002 5 . . 0
56
Trailer Control Valves1.
Trailer Control Valve with predominance 973 008 . . . 0
Purpose:To control the trailer’s twin-line brakingsystem together with the dual-circuitbrake valve and the hand brake valve forspring-brake actuators.
If a line ruptures, or the trailer’s controlline has not been connected, actuation ofthe brake valve on the motor vehicle willcause a reduction of the air supply fromthe towing vehicle to the trailer and a si-multaneous pressure reduction in thetrailer’s supply line.
Operation:a) Actuation from the dual-circuit
brake valveWhen the brake valve on the motor vehi-cle is actuated, compressed air flowsfrom service braking Circuit 1 throughPort 41 into Chamber B, acting on piston(e). This moves downwards, closing theoutlet (g) and opening the inlet (k) as itsits on the valve (j). The air supply fromPort 11 flows through Chamber G to Port2 and pressurizes the trailer’s controlline, the pressure being similar to that in
service brake Circuit 1, with a predomi-nance (1 bar max.) set by means of theadjuster screw (f).
The pressure building up in Chamber Dacts on the underside of piston (e). Dueto the difference in the effective areas ofpiston (e), the actuating pressure inChamber C and the force of the pressurespring (l) causes that piston to move up-wards. The valve (j) following piston (e)closes the inlet (k) and a neutral positionhas been reached. At full brake applica-tion, the pressure acting on the upperside of piston (e) is greater and the inlet(k) remains open.
When the pressure in Chamber B is in-creased, piston (b) is forced downwardsagainst the pressure of the control spring(d). The valve (c) is opened by the ad-juster screw (f) and the actuating pres-sure then building up in Chamber Csupports the downward control of piston(e). This can cause the output pressureat Port 2 to be lower than the actuatingpressure at Port 41. When the adjuster
57
Trailer Control Valves 1.screw (f) is turned anti-clockwise, for in-stance, the pressure in Chamber C is re-duced, and to maintain the balance, theoutput pressure is increased.
Simultaneously with the processes atPort 41, Chamber A is pressurized fromthe service braking circuit through Port42. Since, however, the force generatedby pressurizing Chambers B and Cwhich acts on the upper side of piston (e)is greater, the position of piston (a) is ir-relevant. If a defect causes the servicebraking Circuit 1 to fail, only Port 42 ispressurized from Circuit 2. The pressurethus building up in Chamber A forcespiston (a) downwards and pushes piston(e) ahead, and the trailer’s control linereceives its pressure as describedabove, albeit without any predominance.
b) Actuation from the hand brakevalve
The graded evacuation of the spring-brake actuators through the hand brakevalve causes the pressure in Chamber Fto be reduced accordingly through Port43. The supply pressure at Port 11 nowbeing higher forces piston (h) upwards.Port 2 is then pressurized as for Cham-ber A if service braking Circuit 1 fails.
When the braking process is ended,Ports 41 and 42 are evacuated again, orPort 43 pressurized. This causes pistons(a and e), and piston (h) (by the pressurein Chamber D) to return to their originalpositions. Outlet (g) opens and the com-
pressed air in Port 2 is evacuated to at-mosphere through the tubular piston (h)and Vent 3.
c) Safeguard Against Rupture OfThe Pilot Line
When the braking system is being filledwith compressed air, the air supply flowsthrough Port 11 and Chamber G to Port12 and from there to the automatic ‘Sup-ply’ hose coupling.
When the brakes are actuated, an actu-ating pressure is built up through Port 2in the line leading to the ‘Control’ hosecoupling, the required air being fed infrom Port 11. This causes the pressureabove the piston (3) to fall slightly. At thesame time, compressed air from Port 41is fed beneath piston (i) through Duct E.The pressure in Chamber G rises again,causing the piston to be forced down-wards (play motion to prevent piston (i)from getting stuck).
If a rupture of the trailer’s control line pre-vents pressure building up at Port 2, pis-ton (i) remains in its upper position andblocks the passage leading to ChamberG. The air supply from Port 11 to Port 12is throttled and the pressure in the trail-er’s supply line (Port 12) is reducedthrough the open inlet (k) at the point ofrupture in the trailer’s control line, thuscausing automatic braking of the trailer.
58
Trailer Control Valves1.
Trailer Control Valve with predominance and 2/2 Way Valve 973 009 . . . 0
Purpose:To control the trailer’s twin-line brakingsystem together with the dual-circuitbrake valve and the hand brake valve forspring-brake actuators.
If a line ruptures, or the trailer’s controlline has not been connected, actuation ofthe brake valve on the motor vehicle willcause a reduction of the air supply fromthe towing vehicle to the trailer and a si-multaneous pressure reduction in thetrailer’s supply line. This process causesimmediate automatic braking of the trail-er.
Operation:When the braking system is being filledwith compressed air, the air supply flowsthrough Port 11 into the 2/2-way valveand acts on piston (k). This is forced up-wards into its upper neutral end positionagainst the force of pressure spring (l)and supported by the pressure spring (j).Through duct (i), the air supply flows intoChamber D to Port 12 and from there
through Port 12 to the automatic ‘Supply’hose coupling.
a) Actuation from the dual-circuitbrake valve
When the brake valve on the motor vehi-cle is actuated, compressed air flowsfrom service braking Circuit 1 throughPort 41 into Chambers A and F, actingon pistons (a and k). Piston (a) movesdownwards, forcing piston (b) down. Aspiston (b) sits on the valve (g), the outlet(e) is closed and the inlet (f) is opened.The air supply flows through Chamber Bto Port 22 and pressurizes the trailer’scontrol line, the pressure being similar tothat in service brake Circuit 1, with a pre-dominance of 0.2 ± 0.1 bar, this beingadjustable by means of the adjusterscrew (d).
At the same time, compressed air flowsinto Chamber G through the hole (c),moving piston (m) against the force ofthe spring. The valve (n) sits on the ad-juster screw (d), opening the passage to
59
Trailer Control Valves 1.Chamber E. The air flows into ChamberE and supports the forces acting on theunderside of piston (b).
The pressure building up in Chambers Band E acts on the different effective are-as of piston (b), pushing it upwards, to-gether with piston (a), against theactuating pressure in Chamber A. Thevalve (g) following pistons (b and a) clos-es the inlet (f) and a neutral position hasbeen reached. At full brake application,the pressure acting on the upper side ofpiston (a) is greater and the inlet (f) re-mains open.
Simultaneously with the processes atPort 41, Chamber H above piston (b) ispressurized from the service braking cir-cuit through Port 42. Since, however, theforce generated by pressurizing Cham-ber A which acts on the upper side of pis-ton (a) is greater, the position of pistons(a and b) does not change.
If a defect causes the service brakingCircuit 1 to fail, only Port 42 is pressu-rized from Circuit 2. The pressure thusbuilding up in Chamber H beneath piston(a) forces piston (b) downwards. Thiscloses the outlet (e) and opens the inlet(f), and the trailer’s control line is pressu-rized accordingly, albeit without any pre-dominance.
Within the range of partial brake applica-tion, the pressure building up in Cham-bers B and E pushes piston (b) upwardsonce again. The inlet (f) closes and aneutral position has been reached. At fullbrake application, the pressure in Cham-ber H is greater and the inlet (f) remainsopen.
In the event of a rupture of the trailer’scontrol line (Port 22), no pressure buildsup in Chambers B and E when the serv-ice braking system is actuated. The air isevacuated to atmosphere at the point ofrupture through the open inlet (f) andPort 22. This causes piston (k) to bepushed down further by the actuatingpressure acting in Chamber F, throttlingthe supply pressure flowing from Port 11to Port 22. At the same time, the pres-sure in the trailer’s supply line (Port 12)is reduced through the open inlet (f) atthe point of rupture in the trailer’s controlline, causing automatic braking of thetrailer.
b) Actuation from the hand brakevalve
The graded evacuation of the spring-brake actuators through the hand brakevalve causes the pressure in Chamber Cto be reduced accordingly through Port43. The supply pressure in Chamber Dnow being higher forces piston (h) up-wards. Port 22 is then pressurized as forChamber H if service braking Circuit 1fails.
When the braking process is ended,Ports 41 and 42 are evacuated again, orPort 43 pressurized. This causes pistons(a and be), and piston (h) (by the pres-sure in Chamber C) to return to their orig-inal positions. Outlet (b) opens and thecompressed air in Port 22 is evacuatedto atmosphere through the tubular pistonand Vent 3.
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Wendelflex ® - Hose Connection1.Wendelfelx ® -Hose Connection452 711 . . . 0
Purpose:1) Connection of the air brake system of
the tractive unit with that of the semitrailer.
2) Connection of sections of the airbrake system, which have variablelength between themselves.
Construction:Wendelflex is a coiled hose, which ex-pands with length alterations and re-tracts to its original length whenreleased.
From the hose connection to the first coilthe hose is stiffened through an in builtrelical spring which prevents kinking inthis susceptible region.
Wendelflex hose connections need noadditional gantries or supports. TheWendelflex hose connection is made outof black Polyamid 11. For a visual differ-entiation of the hose connections thehose couplings are supplied with col-oured covers.
Polyamid 11 resists all substances oc-curing on vehicles such as e.g. petrole-um products, oils and greases. Thepipes will also withstand alkalis, unchlo-rinated solvents, organic and inorganicacids and diluted oxydizing agents. (Useof chlorinated cleansing agents is there-fore to be avoided). Resistance againstspecial substances can be given on re-quest.
611
Coupling Heads 1.
A1
A2
B1
C1
Purpose:To connect the air brake system of a tow-ing vehicle to a trailer in accordance withEEC regulations. The coupling headsconform to ISO Std. 1728.
Description:Coupling head versions A1, B1 and C1for the supply line have red covers and acentrally cast protrusion to prevent mealcoupling, versions A2 and B2 for theservice line have a yellow cover and acast protrusion on one side to preventmeal coupling. Versions B and C are fit-ted with automatic shut off valves.
Connecting:The coupling heads are connected by lo-cating the guides of both couplings androtating the flexible connected couplingto lock. After locking, a good seal is es-tablished between the coupling heads.
The cast protrusions ensure that con-nections between incorrect couplingsare not made (Refer to chart showingvarious types).
– Coupling C1 with A1, B1 with A1 andB2 with A2.During coupling the sealing ring ofcoupling head type A, opens the au-tomatic shut off valve fitted to types Bor C. A sealed, through connection isthen established. The shutoff valvesclose automatically when the cou-plings are disconnected.
– Coupling A2 with A2.When connecting identical couplingheads without shut off valves. a pres-sure is established between the seal-ing rings.
Coupling Heads for dual line braking system952 200 . . . 0
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Duo-Matic Quick Coupling1.Duo-Matic Quick CouplingFor Trailers452 80. . . . 0
Purpose:To connect the compressed air brakingsystem of the motor vehicle to that of thetrailer.
Operation:When attaching the trailer, handle (b) ispushed downwards; this causes protec-tive caps (a) and (d) to open. The Duo-Matic trailer portion is placed below theprotective caps and handle (b) is re-leased. Torsion spring (e) acts upon pro-tective caps (a) and (d), pushing thetrailer portion against the automatic clos-ing valves (c), causing them to open:Compressed air now reaches the trailer.
Tractor portion
Trailer portion 452 804 012 0
452 802 009 0
Duo-Matic Quick CouplingFor Semi-trailers452 80. . . . 0
Purpose:To connect the compressed air brakingsystem of the semi-trailer tractor to that ofthe semi-trailer.
Operation:When attaching the semi-trailer, handle(b) is pushed downwards; this causesprotective caps (a) and (d) to open. TheDuo-Matic tractor portion is placed belowthe protective caps and handle (b) is re-leased. Torsion spring (e) acts upon pro-tective caps (a) and (d), pushing thetractor portion against the contact sur-face. The automatic shut-off valves (c)open and compressed air reaches thesemi-trailer.
Tractor portion
Semi-trailer portion 452 803 005 0
452 805 004 0
