Valve Magazine - Summer 2011

A collection of essential articles on the ever-changing world of …

ACTUATORS

& Controls

Do you need to brush up on the subject of actuators and controls? Could you use a handy reference guide that contains two dozen articles on all aspects of this critical equipment that helps control valves? Do you have new employees at your plant or facility that could benefit from this collection of articles? Take a look at the variety of topics covered in this 92-page, full-color, spiral bound collection Actuators & Controls, divided into four sections:

1. GENERAL

▫ Discrete Valve Controllers

▫ The Benefits of Diagnostic Software

▫ Gearbox Selection for Manual Valve Actuation ▫ Automated Valve Packages

▫ Choosing Actuators

▫ When Accessories Become Necessities

2. FLUID POWER

▫ Quarter-Turn Pneumatic Actuators

▫ A Diagnostics Strategy for Digital Positioners ▫ Linear Actuators on Gate Valves

▫ Solenoid Pilot Valves for Actuation ▫ Actuation Under the Sea

▫ Pipeline Valve Actuation

▫ Options for Partial Stroke Testing ▫ Rack & Pinion Actuators

▫ Scotch Yoke Actuators

3. ELECTRIC ACTUATORS

▫ Traditional or High Tech Actuators?

▫ Electric Actuator Selection

▫ Fundamentals of Electric Actuator Control

▫ Linear Output With a Rotary Electric Actuator ▫ Electric Control Valve Actuators

4. CONTROLS

▫ Valve Position Monitoring and Smart Discrete Controls ▫ Digital O&M Solutions

▫ Wireless Technology

▫ Control Systems, Controllers & Control Valves

Cost: $89 ($79 for VMA/VRC members) + s/h
Order your copy online through
The VMA Store on www.vma.org.

A compilation of articles on actuators and controls from past issues of Valve Magazine, brought to you by the Valve

Manufacturers Association REFERENCE

SERIES

ACTUATORS & Controls

12ValveEdReferenceSeries: Actuators& Controls ValveEdReferenceSeries: Actuators & Controls13 Thereisno“one-size-fits-all”formu- laforselectingthepropergearbox foramanualvalveapplication;such selectionisalotmoreinvolvedthan obtainingagearboxasfastaspossible atthelowestprice.Byunderstandingafewbasiccon- cepts,valvemanufacturersandendusers cangainapracticalunderstandingofthe technicalaspectsofgearboxdesignthat willhelpthemselectthebestoneforthe job.Mostimportantly,whenend-users eegearboxesas“technical”com- modities,ratherthanoff-the-shelfpur- chases,theywillbetterappreciatethe skillandexpertisethatvalvemanufac- turersexercisewhenselectingthebest gearboxforaspecificsystem. Installingtherightgearboxatthe beginningmakeseveryone’slifebetter, moreproductiveandsafer. ManualValveOperation Mostvalvegearboxesareusedonvalves operatedmanually,soourdiscussionwill focusonthose.Manualvalveactuationisusedpri- marilyinlow-cycleapplicationsor wheresimpleon/offoperationis required.(Insituationsthatrequirehigh-cycleusageorwherecontrolof thepressureorrateofthefluidthrough avalveisnecessary,non-manualor automatedvalveactuationisthenorm. Typically,automatedactuationuses electric,pneumatic,hydraulicorhigh- pressuregasassourcesofpowerfor operation.) Becausemanualactuatorsarereal- lyconsideredcomponentsofthevalves themselves(likethestems,body,pack- ingandseals),theyareusuallyspecified andpurchasedbyoriginalequipment valvemanufacturers. Therearetwobasiccategoriesof manuallyactuatedvalves:thosethatuse Gearbox Selection for Manual Valve Actuation Atfirstglance,manualvalvegearboxesmayseemlikesimple “off-the-shelf”commodities.Butinreality,certaintechnicalaspects ofvalvegearboxdesignandselectionrequireseriousconsideration. BYCLAYHIGHTOWER Largewormgears onmetal-seated butterflyvalves amechanicaladvantagetomultiply humaneffort,andthosethatdonot. Manualactuatorsthatdonotmultiply humaneffortconsistofdirect-drivehand wheels,leversoroperatingnuts. Manualactuatorsthatdousemechan- icaladvantagestoincreasehumaneffort utilizevalvegearboxes. Quarter-turnandMulti-turn ManualGearboxes Manualvalvegearboxesaredesignedfor eitherquarter-turnormulti-turnopera- tion.Quarter-turngearboxesusually incorporatewormgearsandareusedin applicationswherethevalveshafthasto beturned90degreestofullyopenor closethevalve.Typically,suchgearbox systemsareusedonball,butterflyand plugvalvesaswellasondampers.Quar- ter-turn,worm-geardrivenapplications compriseabout80%ofthemanualvalve gearboxmarket.Multi-turngearboxesusuallyincorpo- ratebevelorspurgearingandareused ongatevalvesandsluicegateapplica- tionswherethevalveshaftoritsmatch- ingdrivenutmustbeturnedmanytimes tofullyopenandclosethevalve.They compriseabout20%ofthemanualvalve gearboxmarket. BasicFunctions:Ratiosand MechanicalAdvantages Manualgearboxesareusedonvalves thathavevalve-stemtorquegreaterthan theaveragepersoncangenerate.Aman- ualgearbox’sbasicfunctionisto mechanicallymultiplyhumanforceinput ogenerategreatertorqueoutput.The useofmechanicalgearingincreasesthe torqueoutputbutreducesthespeed. Therefore,valvegearboxesincrease torqueandreducespeed. Eachtypeofgearingused—whether worm,bevelorspur—hasagearratio andamechanicaladvantageassociated withit.Speedreductionisafactorofthe ratio,andtorquemultiplicationisafactor ofthemechanicaladvantage. Theratioisdeterminedbytherelation- shipofthenumberofgearteethbetween thedriverandgearsetsbeingdriven. Ratioscanvarygreatlyandrangefrom 1:1toover25,000: 1,dependingonhow manygearsetsareused.Whenmore thanonegearsetisusedinagearbox, youmultiplyalltheratiostogethertogetheoverallratioofthegearbox. Forwormgearing,theindustrystan- dardisthattheybeselflocking,sothey donotbackwindinmid-strokefromthe torqueofthevalve.Bevelandspurgears typicallydonothavethisrequirement. Themechanicaladvantageisafunction oftheefficiencyofthegearing.Itisthe measureofhowmuchaninputtorqueis multipliedbythegearsettoproducethe outputtorqueofthegearbox.Efficiency canvarygreatlydependingonthetypeof gearboxused.Wormgearsvarythemost andrangebetween20%to40%efficien- cy.Spurgearsareprimarilyabout90% efficient,andbevelgearsaretypically about85%efficient.Forexample,a wormgearwitha40:1ratioandagear- ingefficiencyof30%wouldhavea mechanicaladvantageof12.Thatgear- boxwouldreducethespeedbyafactorof 40andincreasethetorquebyafactorof 12overthehumanoperatorworking directly(Figures1,2and3). BasicSizing Considerations Toproperlysizeagearboxformanualvalveactuation,consid- erthesemajorareas: 1)Torquerating2)Stemacceptance3)Mountingtothevalve 4)Environmentalrequire- mentsEachgearboxhasacatalog maximumoutputtorquevaluefor agivendesignlife.Inotherwords, thegearboxcanproduceamaximum outputtorqueforacertain umberofcycles.Different makersofgearboxes havedifferentdesign- lifeexpectancies.Thetorquerequiredatthestemto seatorunseatthevalveshouldnot exceedthecatalog-ratedvalueofthe gearbox.Oneimportantconsiderationis toensureengineereddesignlife xpectancyisthesameforboththegear- boxandthevalve.Anysystemisonlyas goodasitsweakestlink.Eachgearbox willalsohaveamaximumstemaccept- ance,andthismustbecheckedagainst hevalvestemdiametertomakesurethe gearboxcanbemachinedtoacceptthat sizevalvestem.Topworksmountinginterfaceson valvesvarygreatlydependingontype andmakerofthevalve.Europeandmost otherpartsoftheworldhaveadoptedthe ISOstandardinterfacetogreatlyreduce varietyinmountinggearstovalves. However,intheUnitedStatesvirtually everyvalvemakerhasauniquetop works.Nomatterthetypeofvalve used,therearetwobasicways tomountagearbox:direct orwithadaptation. Direct-mountedgears havethebottomplaneof thegearboxmachinedto matchthetopworksofthe valve,soonlyfastenersare required.Valveswherethis cannotbedonerequireadap- tationtoproperlyandsafely mateupthetopworksofthe valvetothegearbox.Adapting earboxesisanindustry withinitselfthatisservedin theU.S.marketbyadozenor more“bracket”manufactur- ers.Anotherimportantconsidera- tionistheapplicationorenvi- ronmentwherethegearboxand Figure1.Bevelgearcutawayview Figure2.Spurgearcutawayview Figure3.Cutaway viewofawormgear REFERENCE SERES ACTUATORS&Controls 22ValveEdReferenceSeries: Actuators& Controls Forthoseofuswhohavebeenaround foranumberofyears,thisarticleon valveactuatorswillbetoosimplistic— butit’ smeanttobe.Theseasonedprofes- sionalhashadampleexperience—and knowswhatworksandwhatisrequired. Otherthanstayinguptodateonnew developments,heorshecanreadilyspec- ifytheappropriateactuatorforeach application.Butforthosenewtothe scene,thereareafewfactorsthatneed tobelearnedandconsideredbeforetack- lingactuatorselection. Logically,anewbiecouldturntoan experiencedcolleagueforadvice,thereby followingprovenpracticeswhilegaining personalinsight.However,thisapproach workswellonlyifallofthatexperience wasnoteliminatedviaaneconomically inspiredcutbackoraretirement! Hereissomeofthebasicinformation weallneedtoknow: ValveTypes Therearethreebasicvalvetypes:those thatemploylinearmotion,thoseusing rotarymotionandcertainhybridsthat bothliftandturn.Obviously,anactuatormustexhibitthesamemotionasthe valve.Pastthat,thereareconditionsthat willleadtocertainactuatorselections foreachapplication. Manualvs.Automated Regardlessofvalvetype,thefirstconsid- erationiswhetherthevalvewillbeoper- atedmanually(actuatedbyhumanmus- cle)orautomated(actuatedbyadevice thatdoesnotemployhumanmuscle). Someoftheconditionsthataffectthis decisionare:;Valvesize,whichaffectstheability ofahumantoprovidesufficient inputforce;Quantityofactuatorsversusavail- ablepersonneltooperate ;Theon/offorcontrolapplication— howoftenthevalvemustbereposi- tionedandwhetheritmustrespond rapidlytosystemvariables ;Locationandwhetherthevalveis accessible;Environment—temperature,radia- tion,noise,potentialtobeexplo- sive,whetherchemicalsarepresent ;Economics—thelesserpurchasecostofamanualdeviceversusthe costofoperatingpersonnel ;Speedorwhethertheoperationis exceptionallyfastorexceptionally slow ManualOperation Ifthedecisionistousemanualopera- tion,youhaveachoiceofhandle,locking handle,gearboxorchainwheelforvalves locatedaboveandbeyondnormalopera- torreach(Figures1, 2,3and4). Handlesoffersimplicitywheninput forcerequirementsarelow.Gearboxes arenormallyself-lockingandofferhigh outputwithreducedinputforcespread overalongertimeperiod. Acautionregardinghandles:Some valves,particularlybutterflytypes,may exhibithighdynamictorques,which causeavalvetotendtomoveonitsown. Alocking-typehandleisnecessaryfor suchvalves.Careshouldbetaken becauseahighdynamicforcevalvecan suddenlyactwhenthelockisreleased, whichcouldharmtheoperator.Also,ifa valvecontrolsliquidflow,closingittoo fastcancreatedamagingwaterhammer intheline.Thisscenariomostoften occurswhenahandleisused,whilea gearboxlimitsthispossibility. AutomatedOperation Ifthedecisionistoautomatetheopera- tion,thepowersourceneedstobe defined:electric,compressedgasor hydraulicpressure?Then,additional factorstoconsiderinclude: ;Whichpowersourceisreadily availableandmostcommonly employedinthefacility ;Whichmeetsenvironmentaland atmosphericconditions,namely heat,noise,radiation,possible xplosivesituation,corrosion, spacethatisavailable,vibration, seismicloading;Orientationofthevalveandactua- tor(horizontalorvertical) ;Speedoftheoperation—whether it’sfast,sloworundefined ;Accessforrepair;Costoffailure;Processcontrolrequirements— whetherit’son-offormodulating (throttling/proportionalcontrol) ;Dutycycles;Numberofoperationsthatoccur— bothdailyandasatotal ;Requiredfailuremode ;Positionandperformanceofthe sourceandwhatdiagnosticsand feedbackisavailable ;Whethermanualoverrideis required;Whetheremergencyshutdownmay beneeded;Theweightandcenterofgravityof theactuator;Mountinginterfacecompatibility Electricactuators(Figure5)generally providetheabilitytostopatanypointin thetravel.Theyalsoproducefull-rated outputthroughouttravel.Ifelectricisused,youwillneedtomatchthe requiredelectricalpower(voltage,fre- quencyandavailableamperage)towhat isavailable.Temperatureandsurround- ingswillalsoplayarole.Ifanareais hotorwet,youmustassurethewind- ingsandhousingsareappropriate.If ireisapossibility,considerprotective coatings/ covers.Forcorrosiveatmos- pheres,assessthemeritofspecialpaint coatings.Typically,butnotalways,youwillfind electricactuators:;Offerconstantoutputforcetorque values;Aretypicallyconstructedofalu- minum,iron,ductileironand/or steel;Aremorelimitedregardinghigher temperatures;Haveduty-cyclemotorlimitations ;Offerexcellentpartialstrokecapa- bilities;Areself-lockinginlastcontrolled position;Arelimitedregardingspring-gen- eratedfailureposition ;Haveintegralmanualoverride capabilities Compressedgas(pneumatic)actuators (Figures6,7and8)areavailablein single-ordouble-actingversions.Single- actingversionshavespringsthatcon- sumesourcepressureasthespringscom- press,therebyprovidingmorespring forceandlessairforce.Forrotaryver- sions,themechanismusedtoconvertlin- eartorotarymotionalsoimpactsthe outputcharacteristic.Actuatoroutput mustbecarefullymatchedtovalve requirementsatalltravelpositions. Typically,butnotalways,youwillfind pneumaticactuatorsare: ;Offeredinaluminum,castiron, ductileiron,steelandstainless teel ;Employedinbothon/offandcon- trolapplications;Notself-lockingexceptinaspring failposition;Availablewithmanualoverride capabilityonlyasaspecified option;Notduty-cyclelimited ;Operatedatpressuresof100psig orlessbutarecapableofhigher maximumpressures ;Limitedto180ºF(82ºC)butare alsocapableoftemperaturesof 400ºF(204ºC)orabovewithsuit- ablesealsandbushingmaterials Hydraulicactuators(Figure9)areessen- tiallythesameaspneumaticsexceptthey operateonliquidandseeconsiderably higherpressures.Typically,butnotalways,youwillfind hydraulicactuators:;Areofferedwithlinearorrotary motioninbothsingleordouble acting;Areoftenavailablewithaninte- gralelectro-hydraulicpressure source;Operateatpressuresfrom500to 3,000psig Conclusion Weusedtheword“typically”inthisarti- clewhendescribingthevariousactuators becausetherearemanyoptionsandno absolutes.Thekeytoactuatorselection istodefineyourownspecificneedsand thenaskyoursupplierstoconfirmtheir productsarecapableofmeetingthose needs.EDHOLTGRAVERisCEOofQTRCO,Inc. ( www.qtrco.com),Tomball,TX.HeisontheVMA BoardofDirectorsandservesastheActuator LeadonVMA’sEducation&TrainingCommittee. Reachhimatedholtgraver@qtrco.com.Thisarticle originallyappearedintheWinter2010issueof ValveMagazine. ValveEdReferenceSeries: Actuators & Controls23 The Basics of Choosing Actuators BYEDHOLTGRAVEREFERENCE EFERENCE SERES ACTUATORS&Controls Figure6.Diaphragmactuator -linearmotion Figure8.Diaphragmactuator-rotary motion Figure7.Rack&pinionactuator- rotarymotion Figure9.Hydraulic singleactingactuator -linearmotion Figure1.Ahandle Figure4.Achainwheel Figure2.Ahandwheel Figure3.Awormgear Figure5.Electricactuator