ABTH Manual Railtown.pdf

7/29/2019 ABTH Manual Railtown.pdf

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Air Brake &Train Handling

Manual

Version 1.0 January, 2009


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Railtown State Historic ParkAIR BRAKE & TRAIN HANDLING

MANUAL

Page 2 of 44


Copyright 2009 Wayne m. Penn

Air Brake Fundamentals

The railroad airbrake is a combination ofmechanical devices operatedby compressed air and

controlledpneumatically,which acts topress abrake shoe against awheel. Itspurpose in train

handlingistocontrolspeedandslack,stopthetrainandtoholditstopped.Itaccomplishesthisby

dissipating the inertial energy of amoving train or locomotiveby creating a frictional drag, or

retardingforce,onthewheels,thuspreventingacceleration,reducingthetrainsspeed,stoppingits

movement,orholdingitstopped,asdesired.

A Brief History

Thefirsttrainairbrakesystemwasintroduced

in the mid1800s, and was known as the

straightairbrake.Thissystemutilizedanair

pipethroughthelengthofthetrainandflexible

connectionsbetweeneachcar,calledthebrake

pipe,whichwas connected directly tobrake

cylinders on each car. Using a valve on the

locomotive,theEngineercontrolledthebraking

forcebyraisingandloweringairpressureinthe

brake pipe, and thus in each brake cylinder.

Thiswasa tremendous improvementover theprevious practice of Brakemen jumping from

car to car on a moving train to apply hand

brakes.However,thestraightairbrakehadone

major limitation: if the trainbroke in twoor if

thebrakepipeburstorleakedbadly,thebrakes

simply failed to apply.GeorgeWestinghouse,

inventor of the straight air brake, quickly

realizedthis limitationanddevelopedwhathe

called the automatic air brake, which

functionedontheoppositeprinciple:thebrake

pipe was charged with compressed air to

release the trainsbrakes,and itspressurewas

reducedtoapplythem.Theobviousadvantage

to this system was its failsafe nature: if the

brake system was charged, and brake pipe

pressure was lost for any reason, the brakes

wouldautomaticallyapply,notfail.Bythelate1800s,allrailroadsintheUSwererequiredby

law to equip their trains with automatic air

brakes. Though the reliability and features of

themodernautomaticairbrakehaveimproved

significantly, it continues to operate on

Westinghousessamebasicprinciple.


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Railtown State Historic ParkAIR BRAKE & TRAIN HANDLING MANUAL

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Overview of System Function

The air brake system on each car must becharged with compressed air in order to

function. An air brake system that is notchargedissaidtobedry,andwillnotfunction.

Thebrakepipeischargedwithcompressedairfromthelocomotive.Acontrolortriplevalveon each car senses the increase inbrake pipepressure and charges the auxiliary reservoirand emergency reservoirs on the car from theair in thebrake pipe.Any airpressure in thebrake cylinder is released to the atmosphere.The brake system is fully charged whenpressureinthereservoirsoneachcarisequalto

the pressure in thebrake pipe and thebrakepipe ischarged to thesettingof theregulating(feed)valveonthelocomotive.

To make a normal brake application, theEngineer makes a service reduction of thepressure in thebrakepipeusing theautomaticbrake valve. This is also called a serviceapplication, as the brake pipe pressure isreducedatacontrolled,orservice,rate.Oneachcar, the control valve senses the reduction in

brake

pipe

pressure

and

directs

air

from

the

auxiliaryreservoirintothebrakecylinderuntilair pressure in brake pipe and auxiliaryreservoir are again approximately equal. Thisresults in abrake applicationproportionate totheamountofthereduction.Additionalservicereductions result inproportionate increases inbrake cylinder pressure until full equalizationoccurs.This is thepointatwhichpressures inthe auxiliary reservoir and thebrake cylinderareequalandairwillno longer flowbetweenthem. Further service reductions beyond thispointwillnotresultinincreasedbrakecylinderpressureorbrakingeffort.

Toreleasethebrake,theEngineerrechargesthebrakepipeusingtheautomaticbrakevalve.Airflowsbackintothebrakepipeincreasingbrakepipe pressure.On each car, the control valve

senses the increase in pressure and respondsagainby charging the cars air reservoirs and

exhaustingpressureinthebrakecylindertotheatmosphere.

Should thebrakepipepressuredropsuddenlyat a rapid or uncontrolled rate, an emergencyapplicationofthebrakeswillresult.Thiscanbein response to the Engineer placing theautomatic brake valve in the EMERGENCYposition, from the opening of a conductorsvalveonalocomotiveorcarsoequipped,fromthe brake hoses between cars parting orbursting, from a control valve assuming the

emergencypositionduringaserviceapplication(knownasanundesiredemergency,orUDE),from theopeningofananglecock tooquicklywhencuttingairinonacar,orfromanyothersource which causes a sudden and rapidreduction of brake pipe pressure. When thisoccurs,most controlvalvedesigns respondbyconnectingboth the auxiliary and emergencyreservoirs to thebrake cylinder, resulting in ahigher overall cylinder pressure than can beachieved with a full service application. In

addition,most control valvedesigns open thebrake pipe to the atmosphere, reducing thebrake pipe pressure even more rapidly andcausing the control valves on adjacent cars toassume the emergency position in quicksuccession. This speeds the emergencyapplicationdown the lengthof the train.Oncean emergency application has been initiatedfrom any source, theres no stopping it. Anemergencyapplicationcannotbereleaseduntilthe train has stopped and all control valves

reset,aprocessthatcantakeseveralminutes.

KEY FACT: Variations in the brake pipepressure cause the train brakes to apply orrelease. The rate at which the pressure in thebrake pipe drops determines whether aservice or an emergency application results.



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Page 4 of 44


Friction & Adhesion in Braking

Friction is required toboth move and stop a

locomotiveandtrain.Frictionbetweenthewheeland rail isadhesion.A locomotive, through itstractiveeffort,convertshorsepowerintopullingpower. This tractive effort is limited by

adhesion. Likewise, adhesionbetween awheel

and the rail, combined with friction from a

brake shoe,producesadrag force that retards

therotationofthewheels.

Inertialmotion isstoredenergy.Anyattempt to

retard or dissipate this energy through frictionproduces heat. Therefore, not only must therailroad braking system produce the required

retarding force, it must also dissipate the heat

generated by the process. Locomotive and car

wheelshaveaveryhighcapacity toabsorband

radiate the heat created by braking. However,under extreme conditions, it is possible tooverheat both the wheels and the brake

components.Thiscouldcauseabrakefailure,ora

failureofthewheel&axleassembly,whichcould

resultinaderailment.

CoefficientofFriction is thepercentageof thepressureofthebrakeshoepressingagainstthewheel that is converted into RetardingForce.Twotypesofbrakeshoesareinusetoday:cast

ironandcomposition.Composition,orcomp

shoes,arecommononmodernequipment,but

canalsobefoundonhistoricalequipment.Cast

ironshoesaregenerallybeingphasedoutofuse

onmodernequipment,butarestillcommononhistoricalequipment.Cast ironandcompshoeshaveverydifferentbrakingcharacteristics.Witheither style of shoe, the coefficient of friction

decreases as the speed of wheel rotationincreases. Conversely, as the speed of wheelrotation decreases, the coefficient of friction

increases. However, with cast iron shoes, thedifference inbrakingeffortbetweenhigherandlowerwheelspeeds issignificant,whereaswith

comp shoes this difference is much less.

Therefore,with cast iron shoes, amuchhigherbraking force, or heavier brake application, is

required at higherwheel speeds,which, if leftunadjusted as the speed decreases, wouldincrease in retarding force, most likely to the

point of wheel slide. With composition shoes,

the difference in friction between higher and

lower wheel speeds is not as great, and the

brakingeffortoveranyrangeofwheel rotationspeedsremainsrelativelyconstant.

KEY FACT: Friction between brake shoe & wheelmust not exceed the friction between wheel & railor sliding wheels will result. A sliding wheeldelivers less retarding force than a rotating wheelwith a brake properly applied, while causingdamaging flat spots on the wheel. Wet or bad railtends to reduce adhesion & can result in slidingwheels unless braking effort i s properly managed.

Adhesion

FrictionTractive Effort (locomotive)

orInertial Motion (cars)

Retarding Force

Pressure

BrakeShoe

Heat

30% Coefficient of

Friction:

3000 lbs. of Pressureproduces 900 lbs. of

Retarding Force



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Page 5 of 44


Characteristics of Compressed Air

Compressedairismeasuredinpoundspersquareinch,orpsi.Thisrelatestheamountofstored

energyincompressedairtothenumberofpoundsitexertsononesquareinchofsurfacearea.

KeyThingstoNoteAre:

Compressedairexertsforceequallyinalldirections. Whencompressed,airisheated. Ascompressedairexpands,itwillcool. Thepressureofairinaclosedcontainer,whenheated,willincrease. Thepressureofairinaclosedcontainer,whencooled,willdecrease. Allaircontainssomeamountofmoistureintheformofwatervapor. The warmer the air, the greater its potential to hold water vapor.

However,warmairdoesnotautomaticallycontainmoremoisture.

Thecoolertheair,thelessmoistureitcanhold.Aswarmairiscooled,itswatervaporwillcondenseintowater. Airpropagates,ortravels,throughabrakepipeatabout600feetper

second.

Air pressure vented from a small opening in a container or vessel iswilldropfirstatthelocationclosesttothevent. Pressureintherestof

the container will tend to remain higher than that in the immediate

vicinityof theventuntil thevent isclosed.At thispointthepressure

throughoutthecontainerwillequalize. Inanelongatedvessel,suchas

abrakepipe,thischaracteristicismorepronounced.



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Air Flow Properties

Whenachargedbrakepipe isexhausted fromasinglesource,suchas from the locomotivebrakevalve, air nearest the exhaust point drops in pressure first, followedby the airbehind it in the

system.This

tends

to

cause

the

brakes

nearest

the

exhaust

to

apply

first.

The

brakes

farthest

from

the

exhaustportwillapplymuchmoreslowly. Ifabrakepipe isvented fromseveralplacesalong its

length, thepressuredropsmuchmoreuniformly and thebrakes applymore rapidly andevenly

throughoutthelengthofthetrain.

CHARGINGTHEBRAKEPIPE:

Airflowingintothebrakepipefromthelocomotivewillbuildpressureontheheadendfirst.Thistendstocausethe

auxiliaryreservoirsontheheadendtochargefasterthanthoseontherear.

Airpressurerisesthroughoutthelengthofthebrakepipe.Onlongtrainsthepressureontherearwillnotriseashigh

aspressureontheheadend.Thebrakepipeis,however,fullycharged.Thisisknownas brakepipegradient.

MAKINGAREDUCTION:

Duringabrakepipereduction,airtendstoreduceinpressureattheheadendfirst.

BRAKEPIPEPRESSUREREDUCED:

Airpressureequalizesthroughthelengthofthebrakepipe.

BRAKESRELEASED:

Asthebrakesarereleased,thechargingprocessstartsagain.



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Equalizing Valve & Reservoir

The earliest versions of the automatic brake

valvevented

brake

pipe

air

directly

to

the

atmosphere. As train lengths and brake pipe

volumesgrew,abouncebackeffect resulted

whenthebrakevalvewasclosedaftermakinga

service reduction. This happened because air

flowing down the brake pipe towards theexhaust vent had momentum and whensuddenlycutoff,ashockwavewouldbounce

backdown the lengthof thebrakepipe.This

resultedinbrakepipepressureattheheadend

of the train rising as it sought to equalize,

resultingin

the

undesired

release

of

brakes

on

the head end or sometimes the entire train.Westinghouse fixed thisproblemby adding a

small reservoir called the EQUALIZING

RESERVOIR(ER)tothesystem.TheERactsas

a master volume for the brake pipe and

whateverpressureis intheERisduplicated inthebrakepipe.Duringaservicereduction, theautomaticbrake valve now directly vents air

only from the ER. Attached to the ER is an

EQUALIZING DISCHARGE VALVE with a

taperedexhaust

port

controlled

by

an

EQUALIZING PISTON. This combination ofelementscontrols thecutoffofairdischargingfrom the brake pipe during a service

application so as to absorb themomentum of

air rushing towards the exhaust vent and

prevents abounceback wave of air pressure

downthelengthofthebrakepipe.

Whenmaking a servicebrake application, theEngineer now reduces air pressure in the ER,

notthebrakepipe.TheERvolume,beingmuch

smaller than the volume of the entire brake

pipe, is easier to control than venting air

directly from the brake pipe. Reducing thepressure In the ER reduces the pressure in

CHAMBERD, over the top of the equalizing

piston.The

pressure

in

the

brake

pipe

forces

the

piston upward, opening the equalizing

discharge valve, exhaustingbrake pipe air to

the atmosphere until pressure in the ER, and

thus Chamber D, is just slightly higher than

thatof thebrakepipe.Thiswill then force theequalizingpistonbackdownward, closing theequalizingdischargevalve.Thetapereddesign

of discharge valve slows the velocity of the

exhausting air as it closes and prevents any

bouncebackfromoccurring.Thelargervolume

ofthe

brake

pipe

takes

longer

to

vent

than

the

equalizing reservoir, varying from a fewsecondsonshorttrainstoaminuteormoreon

longer trains. This difference canbe observed

on the equalizing reservoir and brake pipe

gauges in thecab,andbeheardasbrakepipe

air exhausts from the equalizing dischargevalveunderneaththebrakevalve.



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Page 8 of 44


Principles of Equalization

Pressurizedair,likewater,isafluidandwillflow,alwaysfollowingthepathofleastresistancefromhigherpressuretolower.Inthestudyanduseofrailroadairbrakes,atmosphericpressureisalways

consideredtobezero.

Equalizationisthepointatwhichairpressuresintwoconnectedvolumesareequal,andairwillnotflowfromonevolumetotheother.Thepressureatwhichequalizationwilloccurisdirectlyrelatedtothecomparativesizesofthevolumesandtheoriginalpressuresofthetwovolumes.

Threepairs ofvolumes are illustratedbelow.Eachvolumeon the left is charged to 70psi. The

volumesontherightcontainzeropsiandarenotconnectedtothechargedvolumesontheleft.In

thetoppair,thevolumesareofequalsize;inthemiddle,theemptyvolumeisonehalfthesizeof

thechargedvolume;inthebottomexample,theemptyvolumeistwicethesizeofthechargedone:

0PSI

70PSI

0PSI

70PSI

0PSI

70PSI

Whenthepairsareconnected,airflowsfromthehigherpressureinthechargedvolumetothelower

pressure intheemptyvolumeuntilequalizationoccurs.Noteonthe illustrationatwhichpressures

equalizationoccurs:onlywhen thevolumesare the same sizedoesequalizationoccurathalf the

originalpressure.Whena largervolume flows toasmallervolume,equalizationoccursathigherpressure;whenasmallervolumeflowsto largerone,equalizationoccursatapressurelowerthanhalftheoriginalpressure:

35PSI

35PSI

60PSI60PSI

25PSI

25PSI



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Effects of Piston Travel on Equalization

Considering the principles of equalization, and the relationship in size between the auxiliary

reservoirand

the

brake

cylinder,

it

is

evident

that

the

length

of

cylinder

piston

travel

will

affect

the

pressure atwhich thebrake cylinder and auxiliary reservoirwill equalize.Assume abeginning

brakepipepressure,andthusauxiliaryreservoirpressure,of70psi.

Auxi liary Reservoir Brake Cylinder

Page 9 of 44

Atthestandardbrakecylinderpistontravelof

eight inches, full equalization occurs at 50

psi.Thismeansthatwithafullservicebrake

application, the maximum brake cylinder

pressurefroma70psibrakepipewillbe50

psi.This is the intendedresult,andthecars

foundation brake rigging is engineered to

maximize

brake

performance

around

this

figure.

70 psi 0 psi

50 psi 50 psi

Normal 8-inch p iston travelEqualize at 50 psi.

Nowpicture apiston travel that is adjusted

too short. That same 70psi brakepipe, and

thus auxiliary reservoirpressure,will result

in a brake cylinderpressure of 60psi. This

createsagreater

braking

effort

than

intended

for the circumstances, and could result in

slidingwheels.

Ifpiston

travel

is

adjusted

too

long,

the

exact

oppositewilloccur.Foranygivenbrakepipe

reduction,thebrakecylinderpressurewillbe

lowerthannormal,andtheresultingbraking

effortwillbedegraded.


70 psi 0 psi

60 psi

60psi

Short 6-inch piston travelEqualize at 50 psi .


70 psi 0 psi

40 psi 40 psi

Equalize at 50 psi. Excessive piston travel


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Effects of Brake Pipe Pressure on Equalization

Aswehaveseen,thepressureatwhichequalizationoccursvariesbasedontherelationshipofsize

between the two volumes. Full equalization is the point at which pressures in the the two

volumes,in

our

case

the

auxiliary

reservoir

and

the

brake

cylinder,

are

equal

and

air

will

no

longer

flowbetweenthem.Normally,fullequalizationresultsfromafullservicereductionofthebrakepipe.

At thispoint, further service reductions inbrakepipepressurewillnot result in increasedbrakecylinderpressureorbrakingeffort.Butwhathappensifweincreasethepressureofthebrakepipe,

andthusthepressureintheauxiliaryreservoir?Assumingnormalpistontravel,thefollowingwill

betrue:

70 psi 0 psi

From a brakepipepressure of 70psi,full

equalization isachievedwitha20psibrake

pipe reduction and results in a maximum

servicebrakecylinderpressureof50psi.

50 psi 50 psi

90 psi 0 psiByincreasingthebrakepipepressureto90

psi,full equalizationwillnowoccurwitha

26psi reduction,and result inamaximum

service brake cylinder pressure of 65psi.

This is a braking effort increase of about

30%overa70psibrakepipe.

65 psi 65 psi

Further increasing brake pipe pressure to

110psi now results in a full equalization

pressure of 78psi.This is achievedwith a

32psireductioninbrakepipepressure.This

isapproximatelya20% increase inbraking

effortovera90psibrakepipe.

Notethat

for

any

brake

pipe

pressure

of

70

psi

or

higher,

the

brake

cylinder

pressure

developed

with normalpiston travelwillbe 2.5 times the amount of the reduction,up to thepoint of full

equalization.As the setting of thebrake pipe pressure in increased, the pressure atwhich full

equalizationoccursalso increases,and thus the totalbrakecylinderpressureavailable for service

braking. However, regardless ofbrake pipe pressure, the 2.5 x (amount of reduction) formularemainsconstantforservicebraking.Thismeansthata5,10or20psireductionwillalwaysproducethesamebrakecylinderpressure,regardlessoftheoperatingbrakepipepressure.

50 psi

110 psi 0 psi

50 psi



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Air Brake System Components

Control Valves

Toapplyandrelease thebrakesandchargea trainsairbrakesystem,eachcarand locomotive is

equippedwithaCONTROLVALVE, sometimesknownasaTripleValveonolderequipment.

The term TripleValve refers to the three functions itperforms: charge, apply and release the

brakes. As triple valve design and function advanced, it evolved into two ormore portions

mountedonamanifoldknownasapipebracket,allofwhichbecameknownasacontrolvalve.Thebrainoftherailroadairbrake,thetripleorcontrolvalveautomaticallysenseschangesinbrakepipepressureandrespondsbycharging,applying&releasingthebrakes.

PLAIN TRIPLE (right): The first widely successful control valve, theplaintripleperformedonlythebasicfunctionsofcharging,applyingand

releasingthebrakes.As train lengthsgrew, theplain triplesuffered from

an inability to apply and release the brakes uniformly on long trains.

Brakestendedtosetupquicklyontheheadend,butmoreslowlyontherear end, and release on the head end first, while brakes on the rear

releasedslowly.Thisoftenresultedinsevereundesirableslackaction.

SCHEDULE K (left & below): Ktypebrake equipment was developed around

1900 inresponse todemandsplacedonairbrake performance by growing trainlengths. Itwas a significant improvement over theplain triple in

that itpropagates,orspeedstherateatwhichareductiontravels

thelengthofthebrakepipebyventingasmallportionofbrakepipe

airto

the

atmosphere

during

an

initial

service

brake

application.

This

is known as quick service, and applies thebrakesmore quicklyandevenlythroughthetrain.TheKalsoslowsthereleaseofbrakesontheheadendofatraintobettermatchtheslowerreleaserateof

brakesontherear.Thesefeaturesreducedundesiredslackactionandimprovedtrainhandling.Ina

significant safety improvement, theKvalvealso introducedhigherbrake cylinderpressure inan

emergencyapplicationbyventingbrakepipeairdirectlyintothebrakecylindertocombinewiththe

auxiliary reservoir volume. This increases brake cylinder pressure in emergency over thatachievable in a fullserviceapplication, and speeds the

emergency application down the

train.K

equipment

is

characterized

by its single unit configuration

(right),althoughitscomponentscanalso be applied separately. Whileusedonsomepassengerequipment,

ScheduleKwasdesignedprimarily

foruseonfreighttrains.



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Schedule LN:

Lastof theTripleValvedesigns,LNwasderived

from the Kstyle valve but developed for use on

passenger equipment. It introduced advanced

featuresmaking it suitable forpassenger trainuse,

mostnotablyGRADUATEDRELEASE.ItalsohasaQUICKACTION featureandhigherbrakecylinderpressure in emergency. GraduatedRelease is the

abilityofthetriplevalvetomodulateorgraduate

thebrakesoff,aswellason.However,thisfeatureis

notusedonfreightequipment.



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Page 13 of 44


Schedule UC:UC isoneof themostcommon types

of air brake equipment found onhistoric passenger cars. It is the first

design

to

utilize

the

CONTROL

VALVE concept, where several

separate components combine to

perform the functions of the triplevalve,plus anumber of othermoreadvanced features. Its innovative

features include QUICK SERVICE,

QUICK ACTION, selectable

GRADUATED RELEASE, rapid

recharge to allow for quick releaseand reapplications of thebrake, and

depletionprotection,

which

reduces

thepossibilityofairbrakefailureduetodepletionofauxiliaryreservoirpressure.

QuickServiceventsa small amountofbrakepipe air to the atmosphereduring an initial serviceapplication,whichspeedstheapplicationdownthelengthofthetrain.

QuickActionopensthebrakepipedirectlytoatmosphereduringanemergencyapplication,rapidlydepletingthebrakepipepressuretoobtainaquickemergencyapplicationthroughtheentiretrain.Theemergencyreservoirisalsoconnected

totheauxiliaryreservoirvolume,whichresultsinahigherbrakecylinderpressurefromanemergencyapplicationthanis

possiblewithafullservicebrakeapplication.

GraduatedRelease,whenenabled,permitstheincrementalbrakerelease,aswellasapplication.Depletion Protection automatically initiates an emergency application if the brake pipe pressure drops belowapproximately50psi.Thisisintendedtoprotectthetrainshouldthebrakesystembecomedepletedthroughleakageor,a

morelikelyscenario,overcyclingthebrakes.Overcyclingcandepleteauxiliaryreservoirpressureifinsufficienttimeis

allowedtorechargethesystembetweenbrakeapplications.UCistheonlyequipmentwiththisfeature.



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Page 14 of 44


AB-Type Brake Equipment:

AB typecontrolvalvesarethegenesisofmodernfreightcar

airbrakes.Though appliedprimarilyon freight equipment

builtafterWWII,ABbrakeequipmentissometimesapplied

on passenger equipment in tourist or demonstration trainoperations.ABconsistsofthreeportions:

PIPE BRACKET: to which the service and emergency

portionsarebolted.

SERVICE PORTION: controls the desired charging of the

reservoirs and the service application and release of the

brakes.Attached to the serviceportion is the releasevalve,whichpermitsmanualreductionordepletionoftheauxiliaryandemergencyreservoirs.

EMERGENCYPORTION:controlstheemergencyapplicationofthebrakesandtheQuickAction

feature,which opens thebrakepipe to the atmosphereduring an emergency application. It also

combinesbothcompartmentsofthecombinedauxiliaryandemergencyreservoirstogiveahigher

brakecylinderpressureinemergency.

AB equipment introduced or further developed a number of significant improvements over

previoustriplevalvedesigns,including:

ImprovedQuickService:ensuresapromptresponsetoserviceapplications.Duringinitialserviceapplications,theABvalveventsasmallamountofbrakepipepressuretotheatmosphere,resultinginanevenandquickapplicationdownalongtrain.

Combined Auxiliary & Emergency Reservoir: Combines the service reservoir and emergency

reservoirfunctions

into

asingle,

unitized

reservoir

with

two

separate

chambers.

High Emergency Brake Cylinder Pressure: By combining both the volumes in the combined

reservoir,a20%higherbrakecylinderpressureinemergencyisachieved.



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Page 15 of 44


Basic Control Valve Operation

Toapplyand releasea trainsbrakesandcharge itsairbrake system,eachcarand locomotive is

equippedwithaCONTROLVALVE(sometimescalledaTripleValveonolderequipment).The

term

Triple

Valve

refers

to

the

three

functions

it

performs:

charge,

apply

and

release

the

brakes.

Astriplevalvedesignandfunctionadvanced,itevolvedintotwoormoreportionsmountedonamanifoldknownasapipebracket,allofwhichbecameknownasacontrolvalve.Thebrainoftherailroadairbrake,thetripleorcontrolvalveautomaticallysenseschangesinbrakepipepressure

andrespondsbycharging,applyingorreleasingthebrakes,asdesired.

Controlvalvesuseasystemofpistonsand/ordiaphragmsattached to internalvalvesandportingmechanisms.Thesepistonsanddiaphragmsusedifferentialairpressurebetweenthebrakepipeand

the auxiliary reservoirs to open and close the valves and ports, admitting and exhausting air

pressuretoandfromtheappropriatechambersinordertoapplyandreleasethebrakes.

FeedGroove

BrakePipe

Pressure

From

Locomotive

BrakeValve

Emer.Res. Aux.Res.

BrakePipe

Exhaust

LESS THANBrake Pipe Pressure

Brake

Cylinder

RELEASE&CHARGING(above):Whenthebrakepipeiscompleteandtheautomaticbrakevalveisinthe

RUNNINGposition,air flowsfromthemainreservoirs tothebrakepipethrough theFEEDVALVE,which

reducesmain reservoirpressure to theoperatingpressureof thebrake system.Air then flows through the

branchpipeoneachcarandtothecontrolvalve.Asthebrakepipepressurerisesabovethatintheauxiliary

reservoir,airpressure forces thepiston into itschargingposition. In thisposition,air flows from thebrake

pipe,through

the

FEED

GROVE

and

into

the

auxiliary

and

emergency

reservoirs.

The

brake

cylinder

is

also

connectedtotheatmosphere,exhaustinganypressureitholds.Becausethefeedgroveopeningissmall,the

brakepipewillchargemorequicklythanwilltheairreservoirsoneachcar.Therefore,thebrakesystemmay

appeartobefullycharged,butairmaystillbeflowingintothereservoirs.Thebrakepipeisconsideredfully

chargedonlywhen thepressures in thebrakepipeandauxiliary reservoirson each carareequaland the

brakepipepressureontherearofthetrainiswithin5psiofthefeedvalvesetting.Fullychargingadrytrain

canrequireconsiderabletime,asmuchasfivetosevenminutespercar,dependingontrainlength.



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SERVICEAPPLICATION(below):TheEngineermovestheautomaticbrakevalvehandlefromtheRELEASE

positiontotheSERVICEposition.Thisexhaustsairfromtheequalizingreservoir,whichopenstheequalizing

valveandreducesthebrakepipepressurealikeamount.Asthebrakepipepressuredropsbelowthepressure

in theauxiliaryreservoir, thehigherauxiliaryreservoirpressure forces thepiston forward,whichclosesoff

thebrakecylinderexhaustandconnectstheauxiliaryreservoirtothebrakecylinder.

LAP(below):Air flowsintothebrakecylinderuntilpressureintheauxiliaryreservoirisjustslightlylower

than the reducedbrake pipe pressure. Brake pipe pressure now pushes the piston into its LAP position,

closingoffallconnectionsbetweenthebrakepipe,theairreservoirsandthebrakecylinder.

Aux.Res.Emer.Res.

Brake

CylinderExhaust

BrakePipe

KEY FACT: Additional service reductions of brake pipe pressure will cause the control valve to againmove into the service position, until full equalization occurs. Full equalization is the point where airpressures in the auxiliary reservoir & the brake cylinder are equal, & air will no longer flow from thereservoir to the cylinder. Further reductions from this point w ill not result in an increase of braking power!

BrakePipe

80PSI

80PSI

90PSI

Exhaust

Brake

Cylinder

10PSI

Aux.Res.Emer.Res.

Page 16 of 44




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SERVICERELEASE(seeRELEASE&CHARGINGillustration):Toreleasethebrake,theEngineerrecharges

thebrakepipebyplacingthebrakevalveintheRELEASEorRUNNINGposition.Airthenflowsbackintothe

brakepipeandreturnstoitsoperatingpressure.Thisagainconnectstheauxiliaryreservoirstothebrakepipe,

rechargingthemtobrakepipepressure,andexhauststhebrakecylindertotheatmosphere.

KEY FACT: Following a SERVICE reduction, the control valve will assume the RELEASE position if thebrake pipe pressure rises only about 1.5-psi above auxiliary reservoir pressure. Care must be taken not tocause an undesired release by inadvertently allowing brake pipe pressure to rise even slightly.

EMERGENCYAPPLICATION(below):Ifanemergencyratebrakepipereductionoccursfromanysource,

thecontrolvalveassumestheEMERGENCYposition,whichconnectsboththeauxiliaryandemergency

reservoirstothebrakecylinder.Thelargervolumeofairfromthesecombinedreservoirsproducesahigher

brakecylinderpressurethanisavailablewithaFULLSERVICEapplication.Controlvalvesalsoopenavent

valve,whichisalargedirectpassagefrombrakepipetoatmosphere.Connectingthebrakepipetothe

atmosphereateachcontrolvalvecausesadjacentcarstorapidlyassumetheEmergencypositionaswell,

acceleratingtheapplicationofthebrakes.

HigherBrake

Cylinder

PressureExhaust

BrakePipe

Aux.Res.Emer.Res.

KEY FACT: Following an emergency application, the vent valve will remain open for up to several minutes,

preventing the engineer from releasing the brakes before the train stops. Do not attempt to release thebrakes following an emergency application for at least two minutes, or until it is known that the vent valveshave all closed. If, when attempting a release, air can be heard blowing from under a car, it is likely that avent valve is still open. Wait a little longer before attempting to recharge the brake pipe.



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Page 18 of

January, 2009

ayne m. Penn

Steam Locomotive

Brake System Components

AIR COMPRESSORS: Steam locomotives are

equippedwitheitherSINGLEPHASEorCROSS

COMPOUNDsteamdrivenaircompressors

TheSINGLEPHASEaircompressoristheoldest

designof steamdriven air compressor. Ithas a

singlesteamcylindermountedverticallyabovea

single air cylinder. The lower air cylinder is

ribbedtofacilitatecooling.Itisdualactingas

each stroke, whether up or down, compresses

air, i.e.: the compression stroke downward is

alsothe intakestrokefor theupwardcycle,and

vice

versa.

A

reversing

valve

is

encased

on

top

of

thesteamcylinder.Thisdesignworkswell,but

is limited in capacity and efficiency when

charginglargeamountsofairforlongtrains.

CrossCompoundAirCompressor

CROSSCOMPOUND air compressor improved

onthesinglephasedesignbyusingsteamtwice,

thus increasing its efficiency, and by

significantlyincreasing

delivery

volume.

This

compressorusestwophasesofsteamexpansion

andofaircompressionandworksasfollows:air

is firstdrawn into the lowpressureaircylinder

andcompressedtoaninitiallowpressurebythe

highpressuresteamcylinder,whichusessteam

atboilerpressure.Theairthenflowstothehigh

pressureair cylinderand is further compressed

bythesteamexhaustingfromthehighpressure

side to the low pressure steam cylinder, thus

compounding theair compression cyclesand

theuseofsteam.

SinglePhaseAirCompressorAirCompressorGovernors:

LEFT:DuplexRIGHT:SinglePressure

COMPRESSOR GOVERNORS: To control the

aircompressor

and

main

reservoir

pressure,

a

governor of either the single pressure or

Duplex type isused.The singlepressure type

simply maintains a constant main reservoir

pressure. The duplex typemaintains a high

low rangeofmain reservoir airpressure, thus

reducingcompressorcycling.

44

Version 1.0

Copyright 2009 W


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A-1 Locomotive Brake Equipment

A1 isaveryearly typeof automatic airbrake

equipment and is found only on the oldest of

preservedlocomotives.Itisthesimplestformofautomaticairbrakeandmayormaynot comewithindependentlocomotivebrakecontrol.

G6AUTOMATIC

BRAKEVALVE:

Provided toapplyand

release the train andlocomotive brakes. Its

positionsare,lefttoright:

RELEASE, RUNNING,

LAP, SERVICE and

EMERGENCY. It has

no HOLDING feature. The function of these

positions is explained under the 6ET

Equipmentdescribedinthefollowingsection.

OPERATION:Referring to the abovediagram,

compressedairflows from theSINGLEPHASEAIR COMPRESSOR, at left, to the MAIN

RESERVOIRS, #3 and #4. Here the heated

compressed air cools andmoistureprecipitates

out,collecting in the reservoirs (whichmustbemanuallydrainedperiodically).Airpressure in

themainreservoirs isregulatedbytheSINGLE

PRESSURECOMPRESSORGOVERNOR,attop

left.Thisgovernormeasuresairpressure in themain reservoirs and cycles the compressor asneededtomaintainthedesiredpressure,which

isnormallybetween 110 125psi.Air atmain

reservoir pressure then flows to the

ENGINEERS BRAKEVALVE. From thebrake

valve,theEngineerchargesthebrakepipe.The

FEEDVALVE regulatesairpressure flowing tothebrakepipe,and isnormally set tomaintain

90 psi (refer to local air brake instructions to

determine the correct pressure for your

particularoperation).Airinthebrakepipeflows

tothePLAINTRIPLEVALVEonthelocomotiveand charges theDRIVERBRAKERESERVOIR,whichfunctionsastheauxiliaryreservoirforthe

locomotive.Toapply thebrakeson theengine,

the Engineermakes a reduction inbrake pipe

pressureusing theEngineersbrakevalve.The

triplevalvesensesthisreductionandadmitsairfrom thedriverbrake reservoir to theDRIVERBRAKECYLINDERS.To release thebrake, the

Engineerrechargesthebrakepipebyplacingthe

Engineers Brake Valve in the RELEASE or

RUNNINGposition.



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6-ET Locomotive Brake Equipment

By far themost common equipment on steam

locomotivesisSchedule6ET.Itissimilarto,but

more

sophisticated

than,

the

older,

simpler

A

1

equipment.The#6and#14equipmentsapplied

todiesellocomotiveswerederivedfrom6ET.It

functionssimilarlytothesequencedescribedfor

A1 equipment on the previous page, but

includesaHOLDINGbrakevalvepositionand

an independent locomotivebrake functionwith

brakecylinderpressuremaintaining.

H6AutomaticBrakeValve

Engineersautomaticbrakevalvepositionsare:

RELEASE:Connects thebrakepipedirectly to

themain reservoirs,bypassing the feed valve,

while holding an automatic set of locomotive

brakes applied.Used primarily for charging a

longdry train. If left in thisposition, thebrakepipecouldbecomeovercharged,thatis,charged

to a pressure greater than the setting of the

FEED VALVE. To alert the Engineer, a

distinctive hiss is audible when the H6

handleisintheRELEASEposition.

RUNNING:Connectsthebrakepipetothefeed

valve,whichreducesmainreservoirpressureto

the

desired

brake

pipe

pressure.

This

is

the

normalpositionforrechargingandreleasingall

brakes,andwhenrunning.

HOLDING: Recharges the brake pipe to the

feedvalvesettingandreleasesthe trainbrakes,

butholdslocomotivebrakes,ifset,applied.

LAP:Closes allbrake pipe connections.Holds

thebrakepipeatthedesiredreduction,butdoes

notmaintainitagainstleakage.

SERVICE:

Vents

EQUALIZING

RESERVOIR

(CHAMBERD)airpressure to theatmosphere,

causingtheEQUALIZINGVALVEtoopenand

reducebrakepipepressurea likeamount.This

appliesthebrakesonthetrainandlocomotivein

proportiontothereduction.

EMERGENCY:Opensthebrakepipedirectlyto

the atmosphere causing a rapid, uncontrolled

reduction ofbrake pipe pressure and thus an

emergencyapplicationofthebrakes.



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S6INDEPENDENTBRAKEVALVE(right):

The independent brake valve operates the

locomotivebrakesseparatelyfromtheautomatic

brakevalve,thus independentlyfrombrakeson

thetrain.

It

is

used

primarily

to

control

the

enginewhen running light, forholding a train

or locomotive stopped, for switching and for

spotting the train or engine. Its secondary use

canbeforcontrollingslack,trimmingastop,for

shortterm speed control or for emergencies.

However, the independentbrake must notbe

used for extended downgrade speed control

otherwise the driver tires could overheat and

comeloosefromthewheelcenters.

TheS6s

positions

and

functions

are:

RELEASE: Forestalls or releases (bails) an

automatic application of the engine brakes,

either service or emergency, following abrake

pipereduction.Thisisaspringloadedposition;

thehandlemustbeheldinpositionmanuallyor

itwillsprintbacktotheRUNNINGposition.

RUNNING: Normal position to carry the

independent brake valve when running.

Releases an independent application of the

engine brakes, but not an automatic or

emergencyapplication.

LAP: Closes all connections in the valve and

holds the selected application of the engine

brakeapplied.Unliketheautomaticbrakevalve,

thispositionwillholdtheenginebrakecylinder

pressureconstant

against

minor

leakage.

SLOW APPLICATION: Normal position for

applying the independent brake, and for

holding the brake applied when the train or

engine is stopped. Produces a smooth but

responsive buildup of locomotive brake

cylinderpressureup to the independentbrake

REDUCINGvalvesetting.

QUICK APPLICATION: As its name implies,

producesarapid

increase

of

brake

cylinder

pressure, up to the setting of the independent

brakeREDUCINGvalve.This is also a spring

loadedposition; thehandlemustbe inposition

manually or it will springback to the SLOW

APPLICATIONposition.



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M3FEEDorREDUCINGVALVE(right): Two

M3pressureregulatingvalvesareutilizedwith

6ET applications: one to regulate brake pipe

pressure,called theFEEDVALVE; theother to

limitindependent

brake

cylinder

pressure,

called the REDUCING VALVE. In both

applications, the M3 valve takes in main

reservoir pressure and maintains output

pressureat itsadjusted setting, typically90psi

for brake pipe and 3545 psi for independent

brakecylinderpressure.

#6DISTRIBUTINGVALVE(below):Theheart

of the 6ET system is the DISTRIBUTING

VALVE,which is typicallymountedunder the

Engineers side of the locomotive cab. Thismultifunction device is the locomotives

CONTROL VALVE and applies, holds and

releasestheenginebrakesinresponsetoinputs

from the automatic and independent brake

valves, as well as changes in brake pipe

pressure.Thedistributingvalvereadscontrol

airpressure from the independentbrake valve

and relays the same pressure into the

locomotive brake cylinders directly from the

mainreservoir.

This

replaces

the

more

basic

functions of the earlier A1 equipment. Most

notably, rather than relying on a limited

auxiliary reservoir volume to supply air to the

engine brake cylinders, the distributing valve

usesthevirtuallylimitlesssupplyofairfromthe

main reservoirs, which gives it the ability to

maintaincylinderpressureagainstleakage.

M3FEEDorREDUCING

Valve

6ETAIRBRAKEGAUGES(below):

Two DUPLEX AIR BRAKE GUAGES, each

indicating two separate functions, provide the

Engineer with information needed to manage

the airbrake system.On the larger gauge, the

redhandindicatesMAINRESERVOIRpressure

and the black hand indicates EQUALIZING

RESERVOIRpressure.

On

the

smaller

gauge,

the

red hand indicates BRAKE CY LINDER

pressureonthelocomotiveonly,whiletheblack

handpointstotheactualBRAKEPIPEpressure.

Gaugesizeandconfigurationmayvarybetween

locomotives, but the arrangement of pointers

shouldalwaysremainthesame.



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No. 6 & 14 Systems Operation

6ETPipingDiagram

Referringtotheabovediagram,compressedair

flowsfromtheAIRCOMPRESSOR,upperright,

to the MAIN RESERVOIRS (MR). Here the

warm compressed air cools and moisture

precipitates out, collecting in the reservoirs

(which must be periodically drained). Air

pressureinthemainreservoirsisregulatedbya

DUPLEX AIR COMPRESSOR GOVERNOR,

shown to the left of the compressor. This

governormonitorsMR airpressure and cycles

the air compressor on and off as needed to

maintainitbetween110and125psi.MRairthen

flows to theAUTOMATICBRAKEVALVEby

tworoutes:onefeedingMRpressuredirectlytothebrakevalve,andtheotherthroughtheFEED

VALVEwhichreducesMRpressure toselected

brakepipepressure.MRairalso flowsdirectly

totheDISTRIBUTINGVALVE,andthroughthe

REDUCING VALVE to the INDEPENDENT

BRAKEVALVE.

INDEPENDENT BRAKE OPERATION: To

apply the brakes on the engine only, the

Engineer moves the independent brake valve

handletotheSLOWorQUICKAPPLICATION

position until the desired brake cylinder

pressure isobtained, as indicated on thebrake

cylinderpressuregauge, thenback to theLAP

position. Sir from the independentbrakevalve

flows to thedistributingvalve,whichresponds

by admitting MR air directly into the brake

cylinders tomatch thepressureof the inputair

pressure. Due to the large volume of air

required to fill the locomotivebrake cylinders,

utilizing a distributing valve to relay airpressure from theMR to the locomotivebrake

cylinders results in a more rapid buildup of

locomotive cylinder pressure than could be

achievediftheindependentbrakevalvefedthe

locomotive brake cylinders directly, and also

maintainscylinderpressureagainstleakage.



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To release an independent application of the

brakes, the Engineer moves the independent

brakevalvehandlefromtheLAPpositiontothe

RELEASE position. This vents control air

pressureto

the

atmosphere.

If

the

Engineer

desires only reduce the independent brake

application but not fully release it, the

independentbrakevalvehandlemaybemoved

back to theLAPposition to retain anydesired

brake cylinderpressure.Thedistributingvalve

will respond by reducing locomotive brake

cylinderpressuretothatselectedbytheEngineer.

AUTOMATICBRAKEOPERATION:Fromthe

automaticbrakevalve,theEngineerchargesthe

brakepipebyplacing the handle in either theRELEASE or RUNNING position. Air flows

from the automaticbrake valve into thebrake

pipeandthencetothedistributingvalveonthe

locomotiveandchargesitstwocontrolvolumes,

whichfunctionastheauxiliaryreservoirforthe

locomotive. Absent any control air pressure

input from the independent brake valve, the

distributing valve will release the locomotive

brakes. If control air input ispresent from the

independentbrake

valve

but

is

less

than

the

maximum allowable brake cylinder pressure,

thedistributingvalvewill releaseanypressure

in the locomotivebrakecylinders tomatch that

of the control air pressure input.Air from the

automaticbrake valve then flows through the

brakepipe to theCONTORLVALVESon each

car, which sense the increase in pressure and

operate to charge the cars auxiliary reservoirs

from the brake pipe and release any brake

cylinder

pressure.

OVERCHARGED BRAKE PIPE: When the

automatic brake valve is in the RELEASE

position, unregulated MR pressure flows

directly to thebrake pipe. While this maybe

useful in charging a long, dry train, thebrake

pipe could become overcharged if the brake

valve is left in this position too long.

OVERCHARGED BRAKE PIPE is a condition

where theairpressure in thebrakepipeand in

the auxiliary reservoirs on each car is higher

thanthe

setting

of

the

locomotive

feed

valve.

Whentheautomaticbrakevalveisplacedinthe

RUNNINGposition,anoverchargedbrakepipe

willgradually leakdown to the setpressureof

thefeedvalve,resulting inareductioninbrake

pipepressureandsubsequentapplicationofthe

brakes.Thiscreatesasituationwherethebrakes

are applied but the brake pipe is at its fully

charged state, leaving no pressure differential

with which to release the brakes. Should this

occur,

the

condition

can

be

corrected

by

one

of

thefollowingprocedures:

1. Secure the train against unintendedmovement. Initiate an EMERGENCY

application from the automatic brake

valve. After the appropriate timeout

interval, recover the emergency

application in the normal manner by

placing the brake valve handle in the

RUNNINGposition.Ifthebrakesdonot

fullyrelease

on

each

car,

repeat

this

processuntiltheydo.

2. If the above procedure is not effective,then initiate another emergency

application of thebrakes todeplete the

brakepipepressure to zero.Ensure the

train is properly secured against

unintended movement, then manually

drain about half the air pressure from

each auxiliary and supply reservoir on

everycar inthe train.Thenrechargethesystem from the automaticbrake valve

usingonlytheRUNNINGposition.After

allowingsufficienttimeforthesystemto

fully recharge, perform a brake test to

verify proper application and release

beforeproceeding.



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SERVICEBRAKEAPPLICATION:Toobtaina

SERVICEbrakeapplication,movetheautomatic

air brake valve handle from RUNNING to

SERVICE and observe the EQUALIZING

RESERVOIRgauge

in

the

cab.

When

the

desired

reduction in pressure is achieved, move the

handletoLAPtocloseoffallportsinthevalve.

Additionalreductionsmaybemadebymoving

the handle from LAP back to SERVICE, then

backagain toLAP,asdesired. In theSERVICE

position,EQUALIZINGRESERVOIRpressureis

vented to the atmosphere. This causes the

EQUALIZING DISCHARGE VALVE to vent

brake pipe pressure to the atmosphere at a

controlled

or

service

rate

of

reduction.

(See

page 9). As brake pipe pressure reduces, the

locomotive distributing valve will apply the

enginebrakesinproportiontothereduction.

RELEASEofanAUTOMATICAPPLICATION:

Independent Brake Release: Following a

service brake application, a locomotive brake

application may be forestalled or released by

momentarily holding the INDEPENDENT

BRAKE VALVE handle in the RELEASE

position. This position is springloaded on thebrakevalvequadrantsothehandlemustbeheld

heremanuallyoritwillreturntotheRUNNING

position. In RELEASE, the independent brake

valve signals the distributing valve to release

anyairpressureintheenginebrakecylinders.

RunningPosition:Moving theautomaticbrake

valve fromLAP toRUNNING feedsMRair to

thebrake pipe through the FEED VALVE.As

brake pipe pressure increases air flows to the

distributingvalve and to the controlvalves oneach car. The control valves then release each

carsbrakecylinderpressureandrechargetheir

auxiliaryreservoirs.Unlessanapplicationsignal

ispresentfromtheindependentbrakevalve,the

distributing valve will also release any air

pressureintheenginebrakecylinders.

Holding Position: Functions the same as

RUNNING except that HOLDING signals the

distributingvalvetoretainenginebrakecylinder

pressurewhilethebrakepipeisrecharged.

EMERGENCY BRAKE APPLICATION: To

reduce the brake pipe pressure as quickly as

possibleandobtainanEMRGENCYapplication,

swiftlymove theautomaticbrakevalvehandle

toEMERGENCY.Inthisposition,CHAMBERD

and the EQUALIZING DISCHARGE VALVE

arebypassed and thebrake pipe is connected

directly to the atmosphere through a large

opening. This produces a rapid, uncontrolled

reduction inbrakepipepressurewhich causes

each cars control valve to assume itsEMERGENCYorQUICKACTIONpositionand

immediatelyapplymaximumbrakingeffort.

RELEASEofanEMERGENCYAPPLICATION:

Once initiated,anemergencybrakeapplication

cannotbe released until the train has stopped

and VENT VALVES on each car have closed.

Control valves so equipped assume QUICK

ACTION during an emergency application

whichopenventvalves that connect thebrakepipe directly to the atmosphere. This helps

speed an emergency application down the

length of a train. Following an emergency

application,ventvalvesremainopenforatleast

60 to 90 seconds,duringwhich time thebrake

pipe cannot be recharged. Once vent valves

have closed, the automaticbrake valve should

beplaced inRUNNING onmost train consists

to recharge thebrakepipe.On longer trainsor

on trains requiring a high volume of air torecharge, the automatic brake valve may be

placed briefly in RELEASE; however, the

Engineermust remainattentive toactualbrake

pipe pressure as indicated on the gauge and

move thehandle toRUNNINGbefore creating

an OVERCHARGED BRAKE PIPE condition.



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Diesel Locomotive

Brake Systems

Diesellocomotiveairbrakesystemstypicallyconsistof:

AIRCOMPRESSOR thatprovidespressurizedairinsufficientvolumestooperatethetrainsairbrakesystem; MAINRESERVOIRStostorecompressedairtooperatetheairbrakesystem. ENGINEERS BRAKE VALVES to operate the train and locomotivebrake systems

eitherindependentlyorinconjunctionwitheachother.

LOCOMOTIVECONTROLVALVE toapplyandreleasethe locomotiveairbrakes inresponsetoinputsfromtheEngineer.

Diesellocomotiveairbrakesystemsaretypicallyconfiguredasfollows:



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26-C Brake Equipment

The 26C locomotivebrake valve is a contemporary self

lapping type that provides a brake pipe reduction

proportionate to themovement of thebrake valve handle

intoanapplicationzone,ratherthanbackandforthbetweenSERVICE and LAP positions. The equipment also has a

PRESSURE MAINTAINING feature that maintains brake

pipepressureatanygiven levelofreductionagainstminor

leakagethatmayoccurinthebrakepipe.Thisfeatureworks

by feedingair to thebrakepipeatwhateverpressure is in

the equalizing reservoir, regardless of the amount of

reduction or minor leakage in thebrake system.Without

pressuremaintaining,evenminorleakageinthebrakepipe

would continue to reduce its pressure, causing a heavier

applicationof

the

brakes

than

desired.

The 26L type automatic brake valve positions and their

functions,fromlefttorightare:

RELEASE: Charges the brake pipe and the

equalizing reservoir to the pressure setby the

TRAINLINEAIRREGULATINGVALVE,which

releasesthebrakes

MINIMUM REDUCTION: Reduces equalizing

reservoirpressure 57psi,which reducesbrake

pipe pressure a like amount. Initiates QUICKSERVICE feature of control valves on the train

and results in about 10 psi. of brake cylinder

pressureoneachcar.

SERVICE or APPLICATION ZONE:Movement into this zone from left to right further reduces

equalizingreservoirandbrakepipepressure.

FULL SERVICE:Thepositionatwhichbrakepipeequalizationwilloccurandmaximum service

brakingeffortisobtained.

SUPPRESSION:Afullserviceapplicationisobtainedinthispositionandanyoverspeedorsafety

controlbrakeapplication,ifequipped,willbesuppressed.

HANDLEOFF: Allconnectionsinthebrakevalveareclosedinthisposition,andthehandlemay

beremoved;brakepipepressureisgraduallyreducedtozero.

EMERGENCY:Knownas theBigHole, thispositionopensa largeanddirectopeningbetween

thebrakepipe and the atmosphere, causing a sudden anduncontrolled reduction inbrakepipe

pressure; also resets thebrake valve following an emergency application from another source.



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SA26 INDEPENDENT BRAKE VALVE: A self

lapping, pressuremaintaining independentbrake is

mounted below the automatic brake valve handle

andprovides independentcontrolof the locomotive

brakesseparate

from

an

application

of

the

train

brakes.Thebrakevalvehastwopositions:RELEASE,

at the far left of the quadrant, and FULL

APPLICATION, at the far right of the quadrant. In

betweenthesepositionsistheAPPLICATIONZONE.

Movement of thehandle to the right into this zone

provides increasingly higher locomotve brake

cylinder pressure until full application is obtained.

Thepressuremaintainingfeaturewillmaintainbrake

cylinder pressure at the desired pressure against

allowable leakage.AQUICKRELEASEorbailoff

feature is incorporated into the valve whereby an

automaticbrake applicationmaybe releasedon the

locomotiveonlybydepressingtheindependentbrake

valve handle downward. Bailingoff reduces locomotivebrake cylinder pressure to the value

called for by the position of the handle in the APPLICATION ZONE. If the handle is in the

RELEASEposition,locomotivebrakecylinderpressurewillbereducedtozero.

TrainlineRegulating

Valve

SA-26 IndependentBrake Valve

TRAINLINEREGULATINGVALVE: LeftoftheEngineersautomaticbrakevalveistheTrainLine

RegulatingValve,orairpressureadjustmentvalve.Thisadjusts the levelofairpressure fed to the

equalizingreservoirandthusthebrakepipe.ThelocalAirBrakeRulestypicallyspecifytherequired

brakepressuresettingforthisvalve.

CUTOFFPILOTVALVE:TwoorthreepositionvalvewithINandOUT,orFRT,PASSandOUT

positions, locatedon the frontof theEngineersautomaticbrakevalve.Cuts theautomaticbrake

valve INorOUT.ThePASSposition cuts in aGRADUATEDRELEASE feature sometimesused

withpassengerequipment.Whencutout,itdisablespressuremaintainingandallhandlepositions

exceptEMERGENCY,which isalways functional.Theautomaticbrakevalve iscutoutwhenunit

trailsinamultipleunitconsist,andwhenperformingairbraketests.

MU2A M/U SELECTOR VALVE: Sets up the #26equipment independentbrake tooperate as the leadunit in a

locomotive consist, or to function properly as a trailing unit

when connected to a lead locomotive equippedwith abrake

scheduleother than 26L.Thisvalve isusually located on the

backside of the locomotive control stand and it is crucial that

thisvalvebesetproperlyfortheintendedservice.



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Operation of the Equipment

Compressed air for the operation of both

locomotive and train airbrakes is providedby

theair

compressor

on

the

locomotive.

On

adiesel

locomotive, the compressor is driven off of the

mainengine.Agovernor loadsandunloads the

compressor, as needed, tomaintain pressure in

themainreservoirsbetween110to140psi.

Air, alongwith anywatervapor it contains, is

drawn into the compressor and compressed,

significantlyraising its temperature.Fromhere,

thehot,moistair isdischargedintoasystemof

pipingknown asCOOLINGCOILS,which are

designed to radiate the heat away.As the airtravels through this piping, any water vapor

will begin to condense into water. On diesel

locomotives, one or more filters or water

separatorsareusuallylocatedatorneartheend

of this piping to trap and remove thiswater.

Typically these filters and separators will be

equippedwithanAUTOMATICBLOWDOWN

to periodically drain any accumulated water

away.Theair,nowcooleranddrier,thenenters

theMAIN

RESERVOIRS

for

storage.

The

stored

airwillcontinue tocool in themainreservoirs,

causing more water vapor to condense.

Thereforethereservoirsareoftenequippedwith

additional moisture drains, either manual or

automatic,todrainoffaccumulatedwater.

From the main reservoirs, air flows to the

Engineers 26C automaticbrakevalve and the

SA26independentbrakevalves.Theautomatic

brake valve controls brakes on both the

locomotiveand

train;

the

independent

brake

valvecontrolsthebrakeonlyonthe locomotive

orthemultipleunitlocomotiveconsist.

CHARGING THE SYSTEM: When the brake

pipe is completeona trainand the26Cbrake

valve is placed in the RELEASE position, air

flowsfromthemainreservoirstothebrakepipe

through the TRAINLINE REGULATING

VALVEthat

regulates

main

reservoir

pressure

to the operating pressure of thebrake system,

which is 90psi for most railroad operations.

However, consult local operating rules or

instructions for theproperbrakepipepressure

settingforyourterritory.

Air then flows through thebrake pipe, to the

CONTROLVALVEonthelocomotiveandeach

car in the train, which senses the increase in

pressure andmoves into its charging position.

In this position, air from thebrake pipe flowsthrough thecontrolvalve into theAUXILIARY

and EMERGENCY RESERVOIRS. Each cars

brakecylinderisalsoventedtotheatmosphere,

releasinganypressureitmayhaveheld.

INDEPENDENT BRAKE OPERATION:When

an independentbrakeapplication ismadefrom

the SA26 independentbrakevalve, control air

pressureissentdirectlytotheJRELAYVALVE

independentofanybrakepipeactivity.

JRelayValve

TheJRelayvalve suppliedwith26Cairbrake

equipment applies and releases the locomotive

brakes inresponsetocontrolairpressure input



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from the independent brake valve or the

locomotivecontrolvalve.TheJRelaymaintains

brake cylinder pressure against any leakage

usingmainreservoirairasitssupplyvolume.

If the SA26 handle is in the APPLICATIONZONE during an automatic brake application

and thebrake cylinderpressure corresponding

with theposition of the independenthandle is

greater than that of the automatic application,

brakecylinderpressurewillbe increased to the

greatervalue.MovingtheSA26handlebackto

the release position will reduce locomotive

brake cylinder pressure to that corresponding

withtheautomaticbrakeapplication.

Depressingtheindependentbrakevalvehandle

activates theQUICKRELEASEorBAIL feature

which, in turn, activates the quick release

portion of the locomotive control valve.When

the bail is actuated, the position of the

independentbrakevalvehandleinthequadrant

will override an automatic or EMERGENCY

APPLCIATION of the locomotive. If the

independent brake valve handle is in the

RELEASE position when the bail is actuated,

locomotive brake cylinder pressure will bereducedtozero.Iftheindependenthandleisin

the APPLICATION ZONE and the bail is

actuated,brake cylinderpressurewilladjust to

correspondwiththepositionofthehandle.

SERVICE APPLICATION:To initiateaservice

application, the Engineermoves the automatic

brakevalvehandle from thereleaseposition to

theMINIMUMREDUCTIONpositiononthe26

Cquadrant.

This

will

reduce

pressure

in

the

EQUALIZINGRESERVOIRbetween5and7psi,

causing the EQUALIZING DISCHARGE

VALVEtoreducethebrakepipepressurebythe

same amount. This will initiate the QUICK

SERVICE function on control valves so

equipped which will vent a small volume of

brakepipeairdirectlytotheatmosphereateach

control valve location, and speed the initial

buildupofbrakecylinderpressureoneachcar.

KEY FACT: After the initial service reduction,

additional brake pipe service reductions can

be obtained by moving the brake valve

handle further into APPLICATION ZONE of

the 26-C quadrant. This wil l cause the control

valves on each car to increase brake cylinder

pressure a corresponding amount unti l FULL

EQUALIZATION occurs. Full equalization is

the point at which air pressures in the

auxiliary reservoir & the brake cylinder are

equal & air no longer flows from the

reservoir into the cylinder. Further brake

pipe pressure reductions from this point will

not result in increased braking power!

RELEASE of SERVICE APPLICATION: To

releaseaserviceapplicationofthebrakes,move

the 26C handle all the way to the RELEASE

positionatthefar leftofthequadrant.Airthen

flows into the brake pipe as described under

CHARGING THE SYSTEM, affecting a release

ofthebrakes.

KEY FACT: With the CUTOFF PILOT VALVE

properly set to the IN or FRT position, partial

movement of the brake valve handle from the

APPLICATION ZONE towards the RELEASE

position will not increase brake pipe

pressure nor affect a release of the brakes.

However, if the cutoff pilot valve is set to the

PASS position, partial movement of the

brake valve handle from the application zonetowards the release position WILL

INCREMENTALLY INCREASE BRAKE PIPE

PRESSURE & RELEASE THE BRAKES, BUT

WILL NOT FULLY RECHARGE THE SYSTEM.

THIS COULD BE VERY DANGEROUS!



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KEY FACT: Following a service reduction, a

control valve will assume its release position

if the brake pipe pressure rises only about

1.5-psi above auxiliary reservoir pressure.

Care must be taken not to cause anundesired release by inadvertently allowing

brake pipe pressure to rise even sligh tly.

EMERGENCY APPLICATION: If anemergencyrate brake pipe pressure reduction

occurs from any source, the EMERGENCY

PORTION of the locomotive control valve

initiatesQUICKACTION. This opens aVENT

VALVE in the emergency portion, connectingthe brake pipe directly to the atmosphere

throughalarge

direct

opening.

Rapid

venting

of

brakepipe air causes adjacent cars emergency

portions and vent valves to rapidly propagate

the emergency rate brake pipe pressure

reduction through the train. The emergencyportion then connects the emergency reservoirto the brake cylinder, which, along with the

volume of air in the auxiliary reservoir,

combines to create a higher overall brake

cylinderpressure.Ifthereservoirswerechargedto 90 psi, cylinder and reservoir equalization

will occur at about 77 psi. in an emergency

application, 13 psi. more than a full service

application.Thequickactionvalveslowlyvents

avolumeofairpressurethroughachokewhileholding the vent valve open. After about 70seconds the vent valve will close. Brake pipe

pressurecannotbegintoberestoreduntilallof

the vent valves on the train have closed.

Therefore, a running release of an emergency

applicationisnotpermitted.

KEY FACT: From a brake system fully

charged to 90 psi., a full-service brake

application is achieved with a 26 psi. brake

pipe reduction. This is the point at which the

auxiliary reservoir & brake cylinder pressures

equalize & will yield a brake cylinder pressure

on each car of about 64 psi. In an emergency

application, the control valve combines the

volumes of both the emergency & auxiliary

reservoirs, resulting in about 77-psi of brake

cylinder pressure on each car.

CRITICAL KEY FACT About 26-C Pressure Maintaining

The MINIMUM REDUCTION position of the 26-C brake valve automatically makes a 5 - 7 psi

reduction in EQUALIZING RESERVOIR pressure which results in a corresponding drop in

brake pipe pressure. This activates the QUICK SERVICE feature on each car & obtains about

10-psi of brake cylinder pressure. However, we know that a reduction as light as 1.5-psi will

activate the control valves on each car, so why dont we just make a 2 or 3 psi reduction to

initiate quick service?

Heres why: remember that in qu ick service the control valve on each car vents a tiny amount

of brake pipe air to the atmosphere. This reduces brake pipe pressure throughout the train

about 4 to-6 psi. Recall that PRESSURE MAINTAINING reads equalizing reservoir pressure &

feeds air to the brake pipe to match it. If the Engineer were to reduce equalizing reservoirpressure only 3-psi & the corresponding drop in brake pipe pressure activated quick service

on each car, the ensuing 4 to 6-psi drop in brake pipe pressure would leave the brake pipe

pressure lower than that of the equalizing reservoir. Pressure maintaining would then

immediately raise the brake pipe pressure back up to match the original 3-psi reduction.

This condition would release the brakes, but leave the Engineer believing a minimum

application was indeed set on the train.



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Schedule 6 & 14 Diesel Locomotive Brake Equipments

Schedule6and itsvariant#14predatethedevelopmentofthe26C

system and are common on older, preserved locomotives in

operation.

Schedule

6

equipment

came

in

several

versions

including

6BL,6DS,6SLand14EL,allofwhichareoperatedessentiallythe

same.Alluseavariantofthe#6automaticbrakevalvewhich,unlike

the selflapping 26C, is a manually lapping valve requiring

movementofthehandlebetweentheSERVICEandLAPpositionsto

affectandholdaservicebrakeapplication.

A more detailed description of system functions is found in the

Schedule6&14TypeSystemsOperationsectionofthismanual.

#6typeautomaticbrakevalvepositionsandtheirfunctions,fromlefttorightare:

RELEASE:A largeanddirectconnectionbetween theMAIN

RESERVOIR and the equalizing reservoir and brake pipe.

Bypasses theFEEDVALVE andprovidesmaximumvolume

air flow into thebrakepipe. If left in thisposition, thebrake

pipemaybecome charged to apressuregreater than thatof

the feed valve setting, resulting in an OVERCHARGED

BRAKEPIPEcondition.

RUNNING:Normalpositionforchargingthebrakepipeand

releasing all brakes. In this position air from the main

reservoir flows to the equalizing reservoir and brake pipe

throughtheFEEDVALVE,therebychargingthesystemtothe

pressure set by this valve. The feed valve maintains a

predetermined pressure in the brake pipe and equalizing

reservoiragainstallowableleakage.

HOLDING:FunctionsthesameasRUNNINGpositionexcept

thatitholdslocomotivebrakesappliedwhilechargingandreleasingthetrainbrakes.

LAP:ClosesallportsinthebrakevalveandholdsbrakesappliedafteraSERVICEapplication.Does

notmaintainagainstbrakepipeleakage,whichcancausefurtherreductioninbrakepipepressure.

SERVICE:Ventspressure inCHAMBERD above theequalizingpiston to the atmosphere in a

controlledmanner.Brakepipepressure then raises the equalizingpiston andbrakepipe air isexhausted through a control orifice to the atmosphere until pressure in brake pipe and the

equalizingreservoirarethesame.

EMERGENCY:Used toobtain themostrapidandheavybrakeapplicationpossible.Connects the

brakepipedirectly to theatmospherecausinga rapid,uncontrolleddrop inbrakepipepressure.

Thisinitiatesanemergencyapplicationofthetrainbrakes.



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Schedule6independentbrakevalvesmaybeof

theselflappingormanuallappingtype:

SELFLAPPING (left): The selflapping

independent brake valve has two positions:RELEASE, at the far left of the quadrant, and

FULL APPLICATION, at the far right of the

quadrant. In between these positions is the

APPLICATIONZONE.Movementofthehandle

to the right into thiszoneprovides increasingly

higher locomotvebrake cylinder pressure until

full application is obtained. A PRESSURE

MAINTAINING feature will maintain brake

cylinderpressureatthedesiredpressureagainst

allowableleakage.

A

QUICK

RELEASE

or

bail

off feature is incorporated into the valve

whereby an automaticbrake application on the

locomotiveonlymaybe releasedbydepressing the independentbrakevalvehandledownward.

Bailingoffreleases theautomaticapplicationon the locomotiveconsistandreduces locomotive

brakecylinderpressuretothevaluecalledforbythepositionofthehandleintheAPPLICATION

ZONE.IfthehandleisintheRELEASEposition,locomotivecylinderpressurewillbereducedtozero.

MANUAL LAPPING: The laptype independent

brakevalvehasfourpositions:

RELEASE: Releases an automatic brakeapplicationonthelocomotiveonly.

RUNNING: Releases an independent brake

application and is thenormalposition inwhich

thebrakevalveiscarried.

LAP: Closes all ports on the brake valve and

holds a independent application of the brakes

againstallowablebrakecylinderleakage.

SLOWAPPLICATION:Appliestheindependent

brakeatanormalorservicerate.

QUICKAPPLICATION:Utilizesaslightlylarger

port opening in the brake valve to obtain a

somewhat more rapid application of the

independentbrake.



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Other Air Brake Components &

Their Functions

Trainbrakesconsistofindividualcarbrakeapparatus,connectedbyasingleairlineknownasthe

brakepipe,which,combinedwiththelocomotivesindependentairbrake,formthecompletetrainbrake system.Each car is typicallyequippedwith the following,or someother similar,airbrake

systemcomponents:

AIR BRAKE GAUGES (right): The most important

information sources the Engineer will refer to are the

locomotiveairgauges.Theseprovide informationon the

statusofthemostimportantsystemtheEngineeruses:the

brakes. These gauges are called duplex gauges, each

with a red and a white needle, and each display two

functions.ThegaugeontheleftwillalwaysdisplayMAIN

RESERVOIR pressure (RED needle) and EQUALIZING

RESERVOIRpressure(WHITEneedle).Thegaugeon the

rightwillalwaysdisplaytheBRAKECYLINDERpressureofthelocomotive(REDneedle)andthe

BRAKE PIPE pressure (WHITE needle). Note that the equalizing reservoir and brake pipe

indicationsarealwaysonseparategaugesandtheneedlesarebothwhite.

ANGLECOCK(left):valveateachendofthecartocloseoffthebrake

pipe. Anglecocksaretheonlyairvalveonrailroadequipmentthatare

openwhen thehandle is inlinewith the flowofair;otherair cocks,

such asbranch pipe cutout cocks, are openwhen their handles are

perpendicular,or90degrees,fromtheflowofair;

DIRT COLLECTOR/CUTOUT COCK (right): a combinationair filtering

andcutoutvalvelocatedonthebranchpipebetweenthebrakepipeanda

cars controlvalve.Usedtocutoutacarsairbrakesfromthesystem.

BRAKECYLINDER(left):acylinderand

piston which, when filled with

compressed air, imparts its force on the

foundation brake rigging to apply the

brake shoes against the wheel. The

cylinder shown in the photo is applied, with the piston rod

extendedoutfromthecylinderbody.



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DEAD ENGINE DEVICE:

Facilitates themovement of a

dead locomotive in a train.

This feature will charge the

mainreservoirsfromthebrakepipe,whichpermitstheengine

brakestoworkasifitwereacarinthetrain.Thedeviceconsistsofastrainer/checkvalveandcut

outcock inaconnectionbetween thebrakepipeand themainreservoir.This feature isnormally

cutout.However,whencutin,themainreservoirswillchargefromthebrakepipe,thusproviding

airtooperatethebrakes.

FOUNDATIONBRAKERIGGING(below): asystemofrodsandleversthatconnectthebrake

cylindertothebrakeshoesandpressthemagainstthewheels

JRELAY VALVE (right): Air pressure relay valve

supplied with 26C locomotive air brake equipment.

Appliesandreleases the locomotivebrakes inresponse

tocontrolairpressureinputfromtheindependentbrake

valve or the locomotive control valve using main

reservoir

air

as

its

supply

volume.



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MAIN RESERVOIR AUTOMATIC BLOWDOWN (right): a

device on most diesel locomotives attached to the main

reservoirs toautomaticallydrainoffaccumulatedmoisture in

thetanks.

RETAINING VALVE (left): a valve on the

endof thebrakecylinderexhaustpipewhich

permits the retention of air pressure in the

brake cylinderwhen thebrakes are released.

Usedforbrakingonlongorheavygrades.

TRUCKCUTOUTCOCKS (notshown):Locatedunder therunningboardabove

eachtruckisableedtypecutoutcockwhichwillcuttheaircommunicationtothat

trucksbrakecylindersout.Thisistobecutinatalltimesduringnormaloperation.

Thebrakesonalocomotivetruckshouldneverbecutoutunlessofaseverefailure

oftheairbrakesystemthatmakesitunsafetomovetheunitunlessonetruck,and

normorethanonetruck,iscutoutofthesystemanditsbrakesdonotapply.



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General Principles

of

Air Brake & Train Handling

Charging the Brake Pipe

Auxiliary, emergency and control air reservoir volumes on cars and locomotives are charged

throughsmallopenings inthecontrolordistributingvalvecalledchargingchokesorchargingports.

Because theseopeningsaresmallbydesign,airpressure in thebrakepipewillusually rise to its

operatingpressuremorequicklythantheairreservoirsoneachcar.Therefore,thebrakepipegauge

inthelocomotivemayindicatethedesiredpressure,butairmaystillbeflowingintothereservoirs

oneachcar.This cangive theEngineera false impression that thebrake system is fully charged

when,infact,itisnot.

KEY FACT: The brake system is fully charged ONLY when air pressure in both the brake pipe

& the air reservoirs is equal to the operating pressure set by the regulating valve on the

locomotive & air is no longer flowing f rom the automatic brake valve into the brake pipe.

Time to Propagate Application

FromthetimetheEngineermakesaninitialservicereduction,brakecylinderpressureonthefirst

carisinitiatedinaboutfiveseconds,andinitialbrakecylinderpressureisachievedonthefirstfew

cars in the train in about 15 seconds.However, on the last car of a 50car train, itwillbe seven

secondsbefore thebrake evenbegins to apply and closer to 20 secondsbefore 10psi ofbrake

cylinderpressure

is

achieved.

KEY FACT: Keep in mind that the longer the train, the longer it will take the cars on the rear

end to react to an automatic b rake application.

Downgrade Train Control

A characteristic of regularRailtown train operations is typically the short two or three car train

operatedoverrelativelyheavygrades.On longertrains,theforcebetweentheflangesandtherail

createsverynoticeable curvedrag, reducing the rateatwhich the trainaccelerates.Heavy trains

tendtoacceleratemoreslowlythanlighttrainsduetotheirgreatermassandthustheirresistanceto

changes in their state.A short traincanacceleratequicklywhiledriftingdownhillbecauseof the

lackofcurvedragandreducedmass.

Controlling train speed on downhill grades can be challenging. Gravity is pulling the train

downgradeandbrakingeffortandcurvedragareretarding the trainsacceleration.Theoretically,

theseforcescanbebalancedandatrainsspeedmaintainedconstant.Inthistheoreticalscenario,the

trainstartsoutonthedowngradewiththebrakesreleasedandtheengineerallowsittoaccelerateto



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asafespeed.Theengineerthenmakesabrakeapplicationtochecktheacceleration.Ifthebrakesare

applied to the theoreticaloptimum, thespeedof the trainwillbeheldperfectly incheckwith the

pullofgravityonthedowngradeandremainconstant.Thetrainissaidtobebalanced;however,

inactualpractice,especiallywithshorttrains,thisisrarelypossible.

Whatusuallyoccurs is this: as the trainacceleratesdowngrade, theengineermakesoneormorebrakepipereductionstochecktheacceleration.Thebrakesapplyandthespeedofthetrainbegins

todecrease.Insteadofbalancing,however,thetraingraduallyslowstoaspeedbelowtheoptimum

desired. The engineer then initiates a brake release and the train begins to accelerate again,

necessitating anotherbrake application.On a long downgrade, it is necessary to cycle the air

brakesonandoff:releasethebrakes,thespeedbuilds,applythebrakes,thespeeddecreases.The

frequencyofbrakecyclingmustbeminimized,and the timebetweenapplicationsmaximized, to

give the reservoirs on the cars time to rechargebetween each application. If needed, there is a

reservemargin of air in thebrake system if not fully recharged. Be aware, however, that each

successive brake application without full recharge will be potentially less effective than the

previous. If overcycling continues, eventually brake effectiveness could diminish beyond theminimumrequiredtocontrolspeedorstopthetrainonthedowngrade.

Tolimittheamountofbrakingcyclesneededtocontrolthetrain,retainersareused.Thefunctionof

retainersistoslowthereleaseofairpressurefromthebrakecylindersandtoretainafewpoundsof

air and thus somebraking effort or drag. The use of retainers on downhill grades allows the

engineer to reduce thenumberofbraking cyclesneeded tocontrol the train speed.Retainersare

usuallysetbeforeheavydowngradesandreleasedwhenthegradeallows.

Anengineermustconstantlybeawareofthegradesandcurvesinordertocontrolthespeedofthe

train.Ifagradelevelsofforacurveisencountered,lessbrakingeffortisrequired.Conversely,an

increasing

grade

or

tangent

track

requires

more

braking

effort.

Familiarity

over

the

territory

helps

theengineertoanticipatethebrakingneeds,butevenoverfamiliarterritory,conditionscanchange

thataffecttrainbraking.

Tohandleatrainwell,anengineermustuseallsenses. Whiledriftingdowngrade,itishelpfulto

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