Pneumatics: Shuttle, Twin pressure, Quick Exhaust, Time Delay, FRL

Pneumatics: Shuttle, Twin pressure, Quick Exhaust, Time Delay, FRL

1. Hydraulics & Pneumatics
Unit 5 : Pneumatics
Question & Answers
by
Abhishek D. Patange
Assistant Professor
College of Engineering Pune

2. Question1:
•ExplainconstructionandworkingofShuttlevalve
withschematicdiagramusedinpneumatics.
•Alsoexplainelectricalequivalentcircuit,truth
table,Booleanexpression,applicationforshuttle
valveasORlogicgate.
Answerisgivenonnextpage:

3. **Descriptionisgivenonnextpage
Shuttle Valves (OR Gate)

4. Working:
Ashuttlevalveallowstwoalternateflowsourcestobeconnectedina
one-branchcircuit.ThevalvehastwoinletsP1andP2andoneoutletA.
OutletAreceivesflowfromaninletthatisatahigherpressure.Figure
1.5showstheoperationofashuttlevalve.IfthepressureatP1is
greaterthanthatatP2,theballslidestotherightandallowsP1tosend
flowtooutletA.IfthepressureatP2isgreaterthanthatatP1,theball
slidestotheleftandP2suppliesflowtooutletA.
Application:
OneapplicationforashuttlevalveistohaveaprimarypumpinletP1
andasecondarypumpinletP2connectedtothesystemoutletAThe
secondarypumpactsasabackup,supplyingflowtothesystemifthe
primarypumplosespressure.Ashuttlevalveiscalledan“OR”valve
becausereceivingapressureinputsignalfromeitherP1orP2causesa
pressureoutputsignaltobesenttoA
Shuttle Valves (OR Gate)

5. Shuttle valve as OR Gate
A+B
OR Electric Circuit OR Truth Table
Boolean expression
Application

6. Shuttle Valves application in circuit

7. Question2:
•ExplainconstructionandworkingofTwin
pressure/dualpressurevalvewithschematic
diagramusedinpneumatics.
•Alsoexplainelectricalequivalentcircuit,truth
table,Booleanexpression,applicationforTwin
pressure/dualpressurevalveasANDlogicgate.
Answerisgivenonnextpage:

8. Twin pressure/dual pressure valve (AND Gate)
Valve body
Inlet 1 Inlet 2
Outlet
Reciprocating
spool

9. Working:
ThisvalveisthepneumaticANDvalve.ItisalsoderivateofNonReturn
Valve.Atwopressurevalverequirestwopressurizedinputstoallowan
outputfromitself.Thecrosssectionalviewsoftwopressurevalveintwo
positionsaregiveninfigure.Asshowninthefigure,thisvalvehastwo
inputs1and2andoneoutput.Ifthecompressedairisappliedtoeither
1orinput2,thespoolmovestoblocktheflow,andnosignalappearsat
output.Ifsignalsareappliedtoboththeinputs1and2,thecompressed
airflowsthroughthevalve,andthesignalappearsatoutput.
Application:
Thesevalvetypesarecommonlyassociatedbutnotlimitedtosafety
circuits,forexampleatwopushbuttonoperationsystemwherebyan
operatorisrequiredtousebothhandstoactivatetwopushbuttons,this
wouldensuretheoperatorshandsareoutofreachofanyhazardous
operations.
Twin pressure/dual pressure valve (AND Gate)

10. Twin pressure/dual pressure valve (AND Gate)

11. A*B
Twin pressure valve as AND Gate
AND Electric Circuit AND Truth Table
Boolean expression
Application

12. Twin pressure valve application in circuit

13. Question3:
•Explainconstructionandworkingoftimedelay
valvewithschematicdiagramusedin
pneumatics.
•Explaintheapplicationwithcircuit.
Answerisgivenonnextpage:

14. •It is used wherever delay of operation is required
Time delay valve

15. Time delay valve types

16. Time delay valve types

17. Time delay valve circuit animations

18. Circuit of time
delay valve
•In the circuit the
time delay
valve, holds the
cylinder in the
extended
position for the
pre determined
time, set on the
delay valve
1.4
1.21.4

19. Question4:
•Explainconstructionandworkingofquickexhaust
valvewithschematicdiagramusedin
pneumatics.
•Explaintheapplicationwithcircuit.
Answerisgivenonnextpage:

20. Quick Exhaust Valve
•These valves help mainly the DC valves to quickly
exhaust
•They are used for quick operation of actuators
Air enters from
main line to
cylinder
Air quickly exhausts to
atmosphere

21. Afastexhaustvalve(Figure4.26)isusedtoventcylindersquickly.Itisprimarily
usedwithspringreturn(single-acting)pneumaticcylinders.Thedeviceshownin
Figure4.26aconsistsofamovablediscwhichallowsportAtobeconnectedto
pressureportPorlargeexhaustportR.Itactslike,andhasthesamesymbolas,
ashuttlevalve.AtypicalapplicationisshowninFigure4.26b.
Fastexhaustvalvesareusuallymountedlocalto,ordirectlyonto,cylindersand
speedupresponsebyavoidinganydelayfromreturnpipesandcontrolvalves.
Theyalsopermitsimplercontrolvalvestobeused.

22. A circuit using Quick Exhaust Valve

23. Question6:
•ExplainSpeedcontrolmethodsinpneumatics
andcomparespeedcontrolinhydraulicsand
pneumatics.
Answerisgivenonnextpage:

24. •Itisalwaysnecessarytoreducethespeedofcylinderfrom
maximumspeedbasedonselectedsizeoffinalcontrol
valvetothenominalspeeddependingontheapplication.
•SpeedcontrolofPneumaticCylinderscanbeconveniently
achievedbyregulatingtheflowratesupplyorexhaustair.
•Thevolumeflowrateofaircanbecontrolledbyusingflow
controlvalveswhichcanbeeitherTwowayflowcontrol
valveorOnewayflowcontrolvalve.
•MeterIn[throttlingin]
•MeterOut[throttlingout]
Speed control methods in pneumatics

25. 1V1: Meter In for controlling speed of extension
1V2: Meter In for controlling speed of retraction
2V1: Meter Out for controlling speed of retraction
2V2: Meter Out for controlling speed of extension
Speed control methods in pneumatics

26. Important:[ComparisonofspeedcontrolinHyd&Pne]
StickSlipEffect:
•Thereisalimitationisachievingsmoothmovementof
cylinderwithlowspeedsettingofflowcontrolvalve.This
resultsinjerkymotionofpistonwhichiscalledasthestick
slipeffect.
•Whentheflowcontrolvalveissetforlowflowrates,it
takesconsiderabletimeforthesupplyairtobuilduptothe
requiredpressure[correspondingtotheload]behindthe
piston.Everytimethispressureisreached,thepistonjerks
inthedirectionofmotionwhichresultsinincreasein
cylindervolume.Thisfurtherresultsindropinpressurein
thecylinderandthepistonmomentarilyhaltsuntilthe
pressurebuilduptakesplace.Thisintermittentmotionis
calledastheStickSlipEffect.

27. Speed control methods in pneumatics animations

28. Question6:
•ExplainconstructionandworkingofFRLunitwith
schematicdiagramusedinpneumatics.Draw
detailedsymbol.
•ExplainFilterwithneatsketch.
•ExplainRegulatorwithneatsketch.
•ExplainLubricatorwithneatsketch.
Answerisgivenonnextpage:

30. Filter construction

31. Filter working
•Theconstructionoftypicalcartridgetypefilteralongwithgraphical
symbolsisshowninFigure.
•Itconsistsoffiltercartridge,Deflector,bowl,waterdrainvalve.Filter
bowlisusuallymadeofplasticandtransparent.
•Forpressuremorethan10bar,bowlmaybemadeofbrass.
•Airenterstheinletportoftheairfilterthroughangledlouvers.
•Thiscausestheairtospinasitentersthebowl.
•Thecentrifugalactionoftherotatingaircausesthelargerpiecesofdirt
andwaterparticlestobethrownagainsttheinnerwallofthefilter
bowl.
•Thesecontaminantsthenflowdownintothebottomofthefilterbowl.
•Abafflepreventsturbulentairfromsplashingwaterontothefilter
element.Theair,whichhasbeenpre-cleanedinthisway,thenpasses
throughthefilterelement,wherethefinedirtparticlesarefilteredout.
•Thesizeofthedirtparticleswhichcanbefilteredoutdependson
meshsizeoffilterelement(usually5-50microns).
•Thecompressedairthenexitsthroughtheouterport.Thepressure
differencebetweeninletandoutletwillindicatethedegreetowhich
thefilterelementisclogged.

32. Regulator construction

33. Regulator working
•ARelievingtypepressureregulatorisshowninFigure,
•Outletpressureissensedbyadiaphragmpreloadedwitha
adjustablepressuresettingspring.
•Thecompressedair,whichflowsthroughacontrolledcrosssectionat
thevalveseat,actsontheothersideofthediaphragm.
•Thediaphragmhaslargesurfaceareaexposedtosecondary(outlet)
pressureandisquitesensitivetoitsfluctuations.
•Themovementofdiaphragmregulatesthepressure.
If the outlet pressure is low
wheneverthemorecompressedairisconsumedonsecondarysideor
loadside,thenloadpressurereduces.Thereforelessforceactson
diaphragm.Theopposinghigherspringforcepushesthediaphragmin
suchawayastomovethevalvediscmoreandpermittingmoreairto
flowtosecondarysideandthusincreasingthepressureagain.
If the outlet pressure is high
wheneverthelesscompressedairisconsumedonsecondarysideor
loadside,thenloadpressureincreases.Thereforemoreforceactson
diaphragm.Theopposinghigherspringforcepullsdownthediaphragm
insuchawayastomovethevalvedisclessandpermittingairtoflowto
ventholeandthusdecreasingthepressureagain

34. Lubricator construction

35. •Theoperationissimilartotheprincipleofthelubricator.
SchematicdiagramisshowninFigure1.6.
•Asairentersthelubricatoritsvelocityisincreasedbyaventurering.
•Thepressureattheventureringwillbelowerthantheatmospheric
pressureandthepressureontheoilisatmospheric.
•Duetothispressuredifferencebetweentheupperchamberandlower
chamber,oilwillbedrawnupinarisertube.
•Oildropletsmixwiththeincomingairandformafinemist.
•Theneedlevalveisusedadjustthepressuredifferentialbetween
acrosstheoiljetandhencetheoilflowrate.
•Theair–oilmixtureisforcedtoswirlasitleavesthecentralcylinderso
thatlargeparticlesofoilisgoesbacktobowlandonlythemistgoesto
outlet.
•Thelubricatorstartstooperateonlywhenthereissufficientflowofair.
•Iftoolittleairisdrawnoff,theflowvelocityatthenozzleisnotsufficient
toproduceanadequatevacuumandhencetodrawoiloutofthe
vessel.
•Onlythinmineraloilmaybeusedinpneumaticsystemlubricator.
Lubricator working

36. Other important questions:
•Contaminationcontrol:Contamination,sourcesof
contamination[Unit4]
•SmallNumericalonstrainer,filters,filterratings.[Unit4]
•FRLunit[Unit5]
•Numericalonaccumulators[Unit2]
•Typesofaccumulators/symbols/working[Unit2]
•Accumulatorapplications/functions/circuits[Unit2]
•TypicalDesignnumericalfor16markson[unit6]