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Slide 2

IntroductionIntroduction

The purpose of flow control in aThe purpose of flow control in ahydraulic system is to regulatehydraulic system is to regulate

speedspeed. All the devices discussed. All the devices discussedhere control the speed of anhere control the speed of anactuatoractuatorby regulating theby regulating theflowflow

raterate..

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Slide 3

Flow rate can be specified in three different waysFlow rate can be specified in three different ways

Volumetric flow rate, Qv,Volumetric flow rate, Qv, is used to calculate the linear speeds of piston rods oris used to calculate the linear speeds of piston rods or

rotational speeds of motor shafts.rotational speeds of motor shafts.

Weight flow rate, Qw,Weight flow rate, Qw, is used to calculate power .is used to calculate power .

Mass flow rate, Qg,Mass flow rate, Qg, is used to calculate inertia forces during periods ofis used to calculate inertia forces during periods of

acceleration and deceleration.acceleration and deceleration.

Different types of flow measurementDifferent types of flow measurement

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Slide 4

Control of flow rate with valvesControl of flow rate with valves

There areThere are eighteight common types ofcommon types ofFCVsFCVs

OrificesOrifices Flow regulatorFlow regulator Bypass flow regulatorBypass flow regulator DemandDemand--compensated flow regulatorcompensated flow regulator

Pressure compensatedPressure compensated-- variable flowvariable flow Pressure and temperature compensatedPressure and temperature compensated Priority valvesPriority valves Deceleration valvesDeceleration valves

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Slide 5

1. Orifice valve1. Orifice valve

Figure 4-1 Orifices

(a) Simple fixed orifice and

(b) Variable orifice flow controls.

It is the mostIt is the mostelementaryelementarymethod formethod for

controlling flow.controlling flow

.

It is also a basicIt is also a basicpressure controlpressure controldevice.device.

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Slide 6

2.2.Flow regulatorFlow regulator

This device consists of anThis device consists of anorifice that senses flow rateorifice that senses flow rateas a pressure drop acrossas a pressure drop acrossthe orifice;the orifice;

a compensating pistona compensating pistonadjusts to variations in inletadjusts to variations in inletand outlet pressures.and outlet pressures.

This compensating abilityThis compensating ability

provides closer control ofprovides closer control offlow rate under varyingflow rate under varyingpressure conditions..pressure conditions..

Figure 4-2 Flow regulator adjuststo variations in inlet and outputpressures.

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Slide 7

3. Bypass flow regulator3. Bypass flow regulator

Figure 4-3 Bypass flow regulatorreturns excess flow from pump to

tank.

In this flow regulator,In this flow regulator,flow in excess offlow in excess ofpreset flow ratepreset flow ratereturns to reservoirreturns to reservoir

through a bypass port,through a bypass port, Flow rate isFlow rate is

controlled bycontrolled bythrottling fluid acrossthrottling fluid across

a variable orificea variable orificeregulated by theregulated by thecompensator piston.compensator piston.

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Slide 8

4.Demand4.Demand--compensated flow regulatorcompensated flow regulator

Fluid is routed at aFluid is routed at acontrolled flow rate to thecontrolled flow rate to theprimary circuit, andprimary circuit, andbypass fluid can be usedbypass fluid can be usedfor work functions infor work functions insecondary circuits withoutsecondary circuits withoutaffecting the primary one.affecting the primary one.

There must be flow to theThere must be flow to theprimary circuit for thisprimary circuit for thistype of valve to function.type of valve to function.

Figure4-4 Demand-compensated flow

control bypasses full pump output to tank

during idle portion of work cycle.

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Slide 9

5. Pressure compensated5. Pressure compensated-- variable flowvariable flow

It is equipped with anIt is equipped with anadjustable variableadjustable variableorifice placed in seriesorifice placed in series

with

a compensator.with

a compensator.The compensatorThe compensatorautomatically adjustsautomatically adjuststo varying inlet andto varying inlet andload pressures,load pressures,

maintaining anmaintaining anessentially constantessentially constantflow.flow.

Figure 4-5 Pressure-compensated; variable

flow-control valve adjusts to varying inlet

and load pressures.

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Slide 10

6.6.Pressure and temperature compensatedPressure and temperature compensated

Because the viscosity ofBecause the viscosity ofhydraulic oil varies withhydraulic oil varies withtemperature (as do thetemperature (as do theclearances between a valve'sclearances between a valve's

moving parts), output of amoving parts), output of aflowflow--control valve may tendcontrol valve may tendto drift with temperatureto drift with temperaturechanges.changes.

To offset the effects of suchTo offset the effects of suchtemperature variations,temperature variations,

temperature compensatorstemperature compensatorsadjust the control orificeadjust the control orificeopenings to correct theopenings to correct theeffects of viscosity.effects of viscosity.

Figure 4-6 Pressure- and temperature-

compensated, variable flow-control valve adjusts

the orifice size to offset changes in fluid viscosity.

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Slide 11

7.7.Priority valvesPriority valves

Figure 4-7 Priority valve supplies fluid

at a set rate to a primary circuit.

A priority valve is essentiallyA priority valve is essentiallya flowa flow--control valve thatcontrol valve thatsupplies fluid at a set flowsupplies fluid at a set flowrate to the primary circuit,rate to the primary circuit,thus functioning as athus functioning as apressurepressure--compensated flowcompensated flow--control valve.control valve.

Flow in excess of thatFlow in excess of thatrequired by the primaryrequired by the primarycircuit bypasses to acircuit bypasses to a

secondary circuit at asecondary circuit at apressure somewhat belowpressure somewhat belowthat of the primary circuit.that of the primary circuit.

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Slide 12

8.8.Deceleration valvesDeceleration valves

used for decelerating aused for decelerating aload driven by aload driven by acylinder.cylinder.

A cam attach

ed to th

eA cam attach

ed to th

ecylinder rod or loadcylinder rod or loadcloses the valvecloses the valvegradually.gradually.

It provides a variableIt provides a variable

orifice th

at graduallyorifice th

at graduallyincreases backpressureincreases backpressurein the cylinder as thein the cylinder as thevalve closes.valve closes.

Figure 4-8 Deceleration valve slows loadby being gradually closed by action of

cam mounted on cylinder load.

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Slide 13

Flow coefficientsFlow coefficients

TheThe flow flow coefficientcoefficient describesdescribes thethe exactexact relationshiprelationshipbetweenbetween pressurepressure dropdrop andand flowflow raterate forfor aa givengivenvalvevalve mathematicallymathematically..

ItIt isis givengiven byby thethe followingfollowing equationequation::

g

VSpCQ(

!

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Slide 14

Application circuitApplication circuit-- Meter inMeter in FCVFCV

A. Extend cylinder. B. Retract cylinder.

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Slide 15

Application circuitApplication circuit-- Meter outMeter out FCVFCV

A. Extend cylinder. B. Retract cylinder.

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Slide 16

ThanksThanks

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Slide 17

What do we mean byWhat do we mean by PneumaticsPneumatics??Pascal's lawPascal's law applies both toapplies both to hydraulicshydraulicsandandpneumaticspneumatics, because a confined gas, because a confined gas

behaves the same as a confined liquidbehaves the same as a confined liquidwith regard towith regard topressure.pressure.

It means the following formula still

holdsIt means t

he following formula still

holdsfor pneumaticsfor pneumatics

F = p . AF = p . A

5.BASIC PNEUMATICS5.BASIC PNEUMATICS5.BASIC PNEUMATICS5.BASIC PNEUMATICS

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Slide 18

ComponentsComponents used in bothhydraulic and pneumaticused in bothhydraulic and pneumaticsystems aresystems are similarsimilar inin constructionconstruction andand functionfunction..

The differences between hydraulics and pneumatics allThe differences between hydraulics and pneumatics allstem from the fact that pneumatics uses astem from the fact that pneumatics uses a compressiblecompressiblegasgas..

Pneumatics Vs. HydraulicsPneumatics Vs. HydraulicsPneumatics Vs. HydraulicsPneumatics Vs. Hydraulics

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Slide 19

ContinuedContinuedContinuedContinued

Hydraulics PneumaticsUses a relatively incompressible liquids Uses a compressible gas (nearly always air)

Slow, smooth motion Quick, jumpy motion

Very precise Not as precise as hydraulics

Self-lubricating Lubricant must be added

Not as clean (some leakage usually exists) Generally cleaner

Pressure of 500 to 5000 psi Pressure of around 100 psi

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Slide 20

Pneumatics usesPneumatics uses air:air: So, what is airSo, what is air??Air is a mixture of gasesAir is a mixture of gases

21 %21 % oxygenoxygen,,78%78% nitrogennitrogen, and, and

1 % other gases such as1 % other gases such as carbon dioxidecarbon dioxide andand argonargon

PneumaticsPneumaticsPneumaticsPneumatics

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Slide 21

Pneumatic circuit elements are classified intoPneumatic circuit elements are classified intofour primary groups.four primary groups.

1.1. Air Supply and Conditioning elementsAir Supply and Conditioning elementsCompressor, Receiver, pressure regulator, Filter, Dryer,Compressor, Receiver, pressure regulator, Filter, Dryer,

LubricatorLubricator

2.2. Input ElementsInput ElementsSwitches, position sensors, valvesSwitches, position sensors, valves

3.3. Processing ElementsProcessing ElementsLogic valves, time delay valves, directional control valvesLogic valves, time delay valves, directional control valves

4.4. Actuating DevicesActuating DevicesCylinders, motors, semiCylinders, motors, semi--rotary actuatorsrotary actuators

Pneumatic ComponentsPneumatic ComponentsPneumatic ComponentsPneumatic Components

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Slide 22

The properties of gas affects air flow.The properties of gas affects air flow.

These properties will greatly influence the design ofThese properties will greatly influence the design ofany pneumatic system.any pneumatic system.

Hence a few fundamental gas laws based on theHence a few fundamental gas laws based on theproperties of gases need to be considered.properties of gases need to be considered.

The three laws are:The three laws are:

1.

1.

Boyles lawBoyles law2.2. Charles lawCharles law3.3. Pascals lawPascals law

Gas lawsGas lawsGas lawsGas laws

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Slide 23

States that, at constantStates that, at constanttemperaturetemperature thethe volumevolumeof a confined gas isof a confined gas isinversely proportional toinversely proportional to

thethe pressurepressure applied onapplied onit.it.

If pressure increases theIf pressure increases thevolume will decreasevolume will decreaseproportionally.proportionally.

Boyles lawBoyles lawBoyles lawBoyles law

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Slide 24

Charles lawCharles lawCharles lawCharles law

States that, at constantStates that, at constantpressurepressure thethe volumevolumeof a confined gas isof a confined gas isdirectly proportionaldirectly proportionalto theto the temperaturetemperature ininit.it.

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Slide 25

Pascals lawPascals lawPascals lawPascals law

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Slide 26

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