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RETROFITTING

VALVE ACTUATORS

A USER’S GUIDE

How to upgrade existing manually operatedand old-technology valves cost-effectively

and conveniently in your facility.

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A USER’S GUIDE

RETROFITTING

VALVE ACTUATORS

By: Chris WarnettRotork Controls, Inc.

19 Jet View DriveRochester, NY 14624

716-328-1550FAX: 716-328-5848

E-mail: info@rotork.comWebsite: http://www.rotork.com

© 1998 by Rotork Controls, Inc. All rights reserved.

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INTRODUCTIONAutomating valve operation

throughout a facility or in keystrategic areas within the plantcan offer substantial cost sav-ings and improvements inefficiency and safety.

Today, the new generationof valve actuators and two-wirecommunication systems providean easy way for virtually anylarge or small plant to costeffectively retrofit their manuallyoperated valves with automatedsystems. Most important, theretrofit often can be accom-plished quickly without the needfor major plant reconstruction orcomplicated reengineering.

Technology has madeadvances in almost every fieldover the last few years, but theadvances in microprocessorsand computer technology havebeen far greater than manyother technologies. For thatreason, we see many processesin the municipal water treatment,power generation, and oil andgas industries advancing, butoften not as rapidly as thetechnology advancements in thecontrol and supervisory systemsthat run these plants. Theadvent of miniaturization and theeffects of cost-reduction havemade the application of controlsystems more powerful and lessexpensive.

Throughout the industrial-ized world, there are a vast

number of installations thatcould benefit from increasedproductivity by the application ofmodern control technology.

By applying new controls toold plants, many benefits can beaccrued. This is the essence ofretrofit.

The purpose of this bookletis to explore the application ofmodern valve actuator andcontrol technology to existinginstallations and to offer insightson how it might benefit yoursituation.BENEFITS OF RETROFIT

The overall benefit ofperforming a comprehensiveretrofit on a plant accrues fromthe ability to operate the plantmore efficiently. Specifically,when we retrofit, we arereplacing manually operatedvalves or old-technology valveoperators with modern valvecontrol equipment.

One of the major advancesof valve actuator technology thathelps make retrofitting a practi-cal reality is that the presence ofmoisture, dirt, and extremes oftemperature do not affect theoperation of today’s generationof automated valves. For ex-ample, the IQ line of electricvalve actuators was designedwith proven “double-sealed”capability, which prevents theingress of moisture or dirt. It alsoprovides non-intrusive operationsuch that the IQ’s electric covers

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do not have to be removed duringconfiguration, commissioning, andresetting. Furthermore, there aresmart capabilities built into theactuator that provide for superiorlevels of around-the-clock monitor-ing and control.

Simply stated, the old-school of thought that valves inhostile or challenging environ-ments must be manuallyoperated is outdated and canreduce a plant’s efficiency andproductivity.

It’s possible to retrofit even very old valves. The old valve in the fore-ground took hours to manually open and close. The retrofitted valve inthe background is on a control system and takes but a few minutes.

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Specifically, valves that arelarge and take a long time or alot of force to operate manuallycan now be operated rapidlyand reliably utilizing the retrofit-ted actuator. The speed ofoperation of any particularvalve can now be selectedwithout the constraint of spaceor the limitations associatedwith how many workers canstand around and operate ahandwheel.

Quite often, valves arelocated high up in buildings ordeep in sumps or pits where itis difficult and impractical forpersonnel to reach them.Sometimes they are located inhostile areas where there are

noxious fumes or liquids,making it physically distressingto operate the valve manually.The manual operation ofvalves is a common cause ofworker injury, particularlywhere there are old valves thatrequire excessive amounts offorce to operate.

When valves are operatedmanually, plant operations aredependent on the humanoperator to ensure that thevalve is in the correct position.This information has to betransmitted back to the controlroom, which, in the past, wasdone by word of mouth –sometimes an unreliablemethod. By retrofitting a valve

When a disasterous flood inundated the Tacoma Public Utilities’ La Grandehydro plant on the Nisqually River in Washington, the Rotork actuatorspictured above “were as good as new,” according to Bill Jones projectmanager for the Nisqually Hydro Project.

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Many valves are located in hostile, hard-to-reach environments. Byautomating them, several benefits result, including less risk of workerinjury, increased productivity, and improved efficiency. Here, a P Rangepneumatic actuator is used to operate a large butterfly valve in a tunnel.

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actuator, the integral positionindicating mechanisms of theactuator enable both local andremote indication of the positionof the valve. In this way, confir-mation of valve closure can betransmitted instantaneously tothe control room.

Once a plant or a section ofa plant has been retrofitted withvalve actuators, then centralizedcontrol can be affected, increas-ing the throughput of the plantand reducing the workhoursspent manually operatingvalves. Retrofitted plants canrun for an increased number ofhours per day, further increasingreturn on investment andefficiency.

There is another substantialbenefit to retrofitting that ad-dresses the world’s increasedconcern about fugitive emis-sions, contamination from spills,and other environmental issues.That is, automated equipmentcan open or close valves underemergency situations, therebyavoiding spills and other acci-dents. Logic controllers can beused to analyze the status offlow control elements and makethe correct selection of whichvalve to actuate in order toprevent accidents. The ad-vanced monitoring capability oftwo-wire communication sys-tems, such as the Pakscan IIEand IIS systems, ensures thatthe motor operated valves are

constantly checked for availabil-ity to react to emergency cir-cumstances.

Most important, retrofitting isnow affordable and convenient.No longer is it necessary for oldplants to engage in a majorphysical renovation orreengineering of their existingprocesses to upgrade to auto-mated valve operation.

With the coupling of modernelectric and fluid power actua-tors to digital control systems,the cost of retrofitting is nowaffordable to large and smallfacilities alike.MOST FACILITIES CANBENEFIT FROM RETROFIT

Almost every type of plantcan accrue some benefit from aretrofit program. Below aresome typical examples. (SeeRotork’s website at http://www.rotork.com for up-to-datecase histories, user comments,and onsite-photos.)Refinery Tank Farms

The inlet and outlet valveson a tank are located adjacentto the tanks themselves. Tanksare generally spread over alarge acreage, therefore operat-ing these valves requires aconsiderable amount of time foran operator to travel to eachvalve and then manually openor close them. Once the appro-priate valves have been set tothe required position, thenpumps can be started to move

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the products from one area toanother.

These installations areideal for retrofit because of thedistances involved, and alsothe catastrophic consequencesof co-mingling or spillage. Byusing electric valve actuatorslinked by Pakscan communica-tion to a central control room,fingertip control of each valvecan be achieved with positiveverification of the position ofeach valve.Water Treatment Plants

There are many watertreatment plants around theworld that have been in con-

stant operation for many years.Some utilize automatic valveswhile others use manualvalves. The older automaticvalves are often powered bywater hydraulics or com-pressed air. Because of theage of this equipment, aconsiderable amount of main-tenance is required due towear and the corrosive effectsof the moisture and/or chlorinein the atmosphere.

The new generation of fluidpower and electric operatorscan reduce maintenancerequirements and streamlinethe backwash operations by

Retrofitting valves on tank farms provides many benefits, including theability to provide for the quick shut-down and start-up of the flow of oilfrom one area to another. Valve automation also provides a much greaterdegree of environmental protection than manually operated valves.

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preprogramming them in aPakscan IIS master station orthe available host computer.Wastewater Treatment Plants

As environmental concernsincrease around the world, theemphasis on clean water setsmore demands on the wastewa-ter facilities. Many wastewaterfacilities can benefit from auto-mation of sections of theirplants, both large and small.Where operations have tocontinue around the clock, thedemands on personnel can bereduced by having processesautomated, substantially reduc-ing or eliminating the need for

personnel to be present.Power Plants

Power plants are an ex-ample of an extremely highcapital cost plant. But, evenwhere the main steam circuitsand generating equipment stillfunction well, important benefitscan result from strategic retrofit-ting in the plant. That is, moderncontrol equipment can signifi-cantly reduce manning levelsand increase plant efficiency.Also, in old plants, space foradditional motor controls maynot be available. Here theintegrated motor starters of theIQ actuator can give great

The Pakscan IIS two-wire communication system offers a cost-effectiveway for water and wastewater treatment plants to obtain the benefits ofvalve automation. An AQ actuator is pictured in the background, and aprogrammable Pakscan IIS master station is at top right.

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benefits for retrofittingfeedwater valves, boiler trimvalves, and many other appli-cations on a power plantwithout the need for additionalmotor controls at the motorcontrol center. Furthermore,load fluctuations can be moreeasily accommodated by usingdigital two-wire communicationtechnology to piggybackautomated valve controls intoexisting DCS systems.FIRST STEPS IN THE RET-ROFIT DECISION PROCESS

Almost every facility canbenefit from automation. Thescale of a retrofit can varyenormously with the type andsize of plant.

Rotork valve actuatorshave been used to automatethe level control on a reservoirutilizing just two valves; theyhave also been used to auto-mate hundreds of valves onlarge tank farm automationupgrades. However in bothcases, the retrofit elements canbe broken down into a fewdiscrete steps.

First there is the selectionof the particular type of valveactuator. This selection isdependent on many externalfactors, including the availablepower source, the requiredmode of operation, the environ-ment, and so forth.

Then the valve actuatorhas to be controlled by some

means. This could range frommanual push-button controls atthe actuator to sophisticateddigital communications linkedto a host computer somedistance away.

These two elements, theactuator and its controlmethod, dictate how to pro-ceed with the retrofit. Regard-less of whether it is one valveor a thousand valves, thedecisions made and the infor-mation required are the same.

Plant owners or theirconsulting engineers usuallyhave made a decision on thetype of power source to beapplied to the automated valve,and the type of control re-quired, such as on/off, modu-lating, or fail-safe. For userswho have not made thatpreselection, the availablepower sources for valve actua-tors usually include three-phase or single-phase electric-ity, shop air supply (usuallyaround 80 psi), line gas for gaspipeline applications, or waterpressure in water treatmentplants. If any of those powersupplies are readily available,then this may dictate theselection of actuator type.

To remotely control valveactuators, there needs to besome source of control powerthat emanates either from thehost controller, the actuatoritself, or a backup or auxiliary

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power supply, such as solarenergy. Once the power supplyhas been determined and thecontrol philosophy has beendefined, then actuator typeselection can be made.

By definition, retrofittingmeans the installation of a valveactuator onto an existing valve.

Valve selection, therefore, isnot a criterion we need to beconcerned about; however, weare most concerned about thetype of valve that needs to beautomated. From an actuatormanufacturer’s point of view,valves can be segregated intotwo types: (1) multi-turn and (2)quarter-turn.

Multi-turn valves includegate valves, globe valves, andsluice gates. Quarter-turn valvesinclude ball valves, plug valves,and butterfly valves as well aslouver and butterfly dampers.

For multi-turn valves, theavailable actuator selection is IQRange, A Range, PAW, PL, andHPL.

For quarter-turn valves,available actuators are IQRange plus quarter-turn gear-box, A Range plus quarter-turngearbox, AQ Range, Q Range,P Range, H Range, R Range,and HPG Range.

Having selected the type ofactuator, the next step is to sizethe correct actuator to thecorresponding valve. Differentvalves require different torque

inputs because of varying size,pressure class, and mechanism.There is a wealth of detailedengineering information on howto size valves (contact Rotorkfor more details).

The category of valvedetermines the sizing proce-dure. For quarter-turn valves,the torque information has to begathered from the valvemaker orfrom a reference database atthe actuator manufacturer. Thetorque for multi-turn valves,however, can often be calcu-lated using tried and provencalculation methods available atthe actuator manufacturer.

Above is an example of a multi-turn valve and IQ actuator.

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Because the power deliv-ered by an actuator is a func-tion of both torque and speed,sizing cannot be completeduntil the required speed ofoperation is known. In mostinstances, gate valves arerequired to operate at the rateof 12 inches per minute. Forquarter-turn valves, a similarrule of thumb suggests valveoperation at a rate of 60 sec-onds for every 12 inches ofvalve diameter. Hence, a 24-

inch gate valve would operatein two minutes and an 18-inchball valve in 90 seconds.

Differing applications may,of course, require higher orlower speeds, and this willaffect the size of the actuator.

Every plant has differentparameters; however, to do asuccessful retrofit, the twofundamental stages of power-ing the valve and then control-ling the valve can be brokendown to give you a road map

The photograph above shows an example of an A Range actuator plusquarter-turn gearbox.

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on how to proceed with yourretrofit.POWERING THE VALVE1. Choosing the Power Source.

The most common sourcesof power for an automatedvalve are electricity and fluidpower. If electric power isselected, a three-phase supplyis required for large valves(usually on pipes 18 inchesand above); however, for smallvalves (on pipes below 18inches), a single-phase supplymay be sufficient.

Usually an electric valveactuator is able to accommo-date any of the common volt-ages. Occasionally, such as withpower plants, 24-volt DC supplyis available and sometimespreferred for emergency operat-ing or black start operation.Rotork is capable of providingDC-powered actuators.

The variations on fluid powerare much greater. First, there arethe varieties of fluid medium, suchas compressed air, nitrogen,hydraulic fluid, or natural gas toconsider. Then, there are thevariations in the available pressureof that medium. With Rotork’s lineof fluid power products, almost allof those variations can be accom-modated; however, there aresome effects on the size and costof the actuator that need to beconsidered.

The higher the appliedpressure of the fluid medium,

the smaller the required cylinder.Typically, smaller cylinders areless expensive for any givenfluid medium.

If you have a choice of powersupply, Rotork can providebudgetary figures comparingelectric motor operators with fluidpower operators, so a cost-baseddecision can be made.2. Examining the Valve Type.

At the inception of the retrofitproject, the valve type needs tobe known so that the correcttype of actuator can be selected.As we mentioned, some valvesneed multi-turn inputs whereasothers need quarter-turn. Thishas a great impact on the typeof actuator selected and, whenconsidered with the power supplyavailable, a rational selection ofactuator type can be made.

In general terms, multi-turnfluid power actuators are a moreexpensive solution than multi-turn electric actuators; however,for rising non-rotating stemvalves, a linear fluid poweractuator may be the suitableselection.

A definitive selection cannotbe made until the power require-ments of the valve are deter-mined. After that decision hasbeen made, then consider thecriteria below.3. Calculating the TorqueRequired by the Valve.

For quarter-turn valves, thebest way of determining the

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torque required is by obtainingthe valvemaker’s torque testingdata. Most valvemakers havemeasured the torque requiredto operate their valves over the90 degrees of operation andmake this information availablefor customers. In addition,Rotork maintains its owndatabase of torque data formany manufacturers and cansize actuators accordingly.

However, the situation formulti-turn valves is different.Multi-turn valves can be brokendown into several groups:• Rising rotating stem valves

(most globe valves).• Rising non-rotating stem

valves (most gate valves).

• Non-rising rotating stemvalves (some waterworks’gate valves).

In each of these cases, themeasurement of the stemdiameter together with the leadand pitch of the valve stemthread is required in order tosize the valve. This informationcoupled with the size of thevalve and the differential pres-sure across the valve can be usedto calculate the torque demand.

Once we have the powersupply defined, the type ofvalve, and the torque demand ofthe valve, then we can look atthe available products that canautomate that particular valve.

You can find a matrix that

Rotork has extensive testing and quality performance capabilities. Thephoto above shows an apparatus that tests the torque, life, and perfor-mance of spring return and double-acting fluid power actuators.

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can assist you in making thatselection in the Appendix ofthis booklet. The availableproducts together with theirtorque range and power re-quirements are shown there.4. Sizing the Actuator.

Once the actuator type hasbeen selected and the torquerequirement of the valve hasbeen determined, then we cansize the actuator using one ofmany available tools.

For fluid power actuators,we match the fluid pressurewith the torque demand andread off the actuator size fromthe torque tables in Rotork’ssizing guide (which is availableby contacting Rotork).

Usually for fluid poweroperators, the speed of opera-tion is not a critical issue, sincethe normal speed of operationof the actuator is fast enoughfor most applications. If neces-sary, fluid power actuators’speed of operation can beincreased by using high-speed(larger capacity) control valvesand piping. Conversely, it canbe reduced by using thestandard controls with theaddition of flow control valving.

The speed of operation foran electric actuator, however,is critical to the sizing selec-tion. On the Rotork IQ sizingtable, the actuator modelnumber is a function of valvetorque demand and output

speed of the actuator.Perhaps the easiest way to

size electric actuators is to useRotork’s CD catalog (which isavailable free of charge bycontacting Rotork). The inter-active CD allows actuatorselection by range, then sizesthe actuator based on valvetorque demand. It also checksto ensure that the actuator canaccept the valve stem.

Once the actuator hasbeen selected, the CD willallow dimensional drawingsand wiring diagrams to beautomatically selected andprinted out for reference. Thereis also an actuator order form,which can be faxed to Rotorkto place an order.5. Adapting the Actuator to theValve.

Having defined the actua-tor, we now have to considerhow that actuator will bephysically mounted onto thevalve when it arrives from thefactory. For this we need todesign appropriate mountingbracketry, so that the weightand the torque reaction of theactuator is absorbed or sup-ported by the valve.

First, the valve topworksneed to be carefully examinedand measured. There mayalready be some kind ofmounting flange in existencethat previously supported anold actuator or gearbox. This

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could be utilized to bolt anadaptation piece between theexisting valve topworks and theactuator mounting base. Suchan adapter can take manyforms, such as a single ordouble plate adapter, a spoolpiece, or a piece of rectangularhollow section.

The bracket not only mustbe able to support the weightof the actuator, but it must alsobe robust enough to take thetorque reaction and the thrustreaction of the valve. The valvetopworks themselves must alsobe robust enough to supportthese forces. Needless to say,extensive experience is abenefit that comes into play inthe design of the bracketry,

which often is critical to thesuccess of the retrofit.

Some valves have noflange at all onto which theactuator can be mounted. Inthose circumstances, a platehas to be welded in place orsome other means of attach-ment needs to be utilized, suchas a saddle bracket.

Another component that isessential to a successfulinstallation is the torque trans-mission element, or drivebushing. On quarter-turnactuators, this is often a cylin-drical intermediate piecebetween the valve stem andthe actuator bore such that akeyway transmits the drivefrom the drive bushing to the

Pictured above is a valve topworks flange and stem onto which anadaptor and actuator will be mounted for a successful retrofit.

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valve stem.Most electric quarter-turn

actuators have their blank drivebushing available for machiningto suit the valve stem; however,fluid power actuators usuallyhave a custom-machined drivebushing made to suit the actua-tor and valve stem. In eithercase, this component can beprovided by Rotork.

For threaded valve stems,such as gate valves, the drivebushing is usually made of analuminum bronze material thatneeds to be threaded with anexactly matching thread to thevalve stem.6. Mounting the Actuator ontothe Valve.

In the mounting operation,the valve, actuator, and mount-ing adaptation come togetherto make the automated valveassembly. The physical mount-ing of the actuator on the valverequires the stem bushing tobe mated with the valve stemwhile the actuator is loweredonto the mounting hardware.Once in position, the actuatorcan be secured by bolts to themounting hardware and henceto the valve itself.

Once the actuator is physi-cally in position on the valve,then the power supply can beconnected to the actuator. Onelectric actuators, this requiresconduit to be connected to theterminal compartment of the

actuator, and the wires to beconnected to the appropriateterminals in the separatelysealed terminal compartment.Fluid power actuators requiretubing containing the fluidpower medium to be con-nected to the control cabinet orto the direction control valveassociated with the fluid poweractuator.

Once the power supply hasbeen connected, then the limitsof travel and other parameterscan be set on the actuator.

For electric actuators,setup has been dramaticallysimplified with the advent ofthe IQ non-intrusive settingfeature. This allows the limitsof travel, torque setting, direc-

Actuator being mounted on valve.

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tion of rotation, and otherparameters to be set using aninfrared setting tool to commu-nicate with the actuator. Duringthe setup procedure, no coversneed to be removed, andhence no moisture or dirt caningress into the electricalenclosure of the actuator.

Limits of travel on the AQand Q quarter-turn electricactuators also can be achievedby adjusting the external me-chanical travel stops located onthe outside of the actuator. Thesame is true for fluid powerquarter-turn valve actuators.

Details of setup procedurescan be found in Rotork’stechnical manuals suppliedwith the actuator.7. Testing and Commissioning.

Once the actuator hasbeen mounted and the travellimits have been set, then,utilizing the local controls and apower supply, the operation ofthe valve can be tested locally.

The normal procedure fortesting an electric operator is tomove the valve into the “Mid”position, then press the“ Open” button. Providing thepower supply is connectedcorrectly, the valve shouldmove into the “Open” positionuntil it reaches the end-of-travel and then stop.

However, if the actuator isconnected to a three-phasesupply and the phases are

reversed, there is a danger thata conventional actuator wouldmove in the opposite directionbecause of phase reversal.This is an extremely badsituation. It means the torqueand position switches are inthe wrong control circuit, andthe valve could run to the end-of-travel and go into a stallcondition causing damage tothe stem or the valve seat.

Fortunately, this will notoccur with a new Rotorkactuator due to the inherentsafeguard provided bySyncrophase, a feature whichautomatically selects thecorrect contactor to energize.Therefore, the motor willalways run in the correctdirection. The protectionswitches are always in effectand no damage can occur tothe valve.

After the motor operatorhas run the valve in the “Open”and “Close” direction confirm-ing correct seating of the valveand functionality of the auto-mated valve package, thencommissioning is completed,and we can turn our thoughtsto remote operation.CONTROLLING THE VALVE

The standard retrofittedvalve can be controlled locallyusing the standard push-buttons supplied with Rotorkelectric actuators, or with thelocal control panel for a fluid

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power actuator. But localcontrol only provides us with asmall part of the benefits ofretrofitting.

A major benefit of using anautomated valve actuator is thecapability of remotely control-ling the valve and gainingstatus on its condition at thecontrol room.1. On/Off Control.

The most basic type ofcontrol for an automated valveis that which tells it to be“Open” or “Closed.” This easily

can be achieved by running apair of wires out to the actuatorfrom the control room.

By applying a voltageacross the wires, we canenergize a contactor coilinitiating motion in an electricvalve actuator, or we canenergize a solenoid coil caus-ing a fluid medium to move afluid power actuator. Thepresence of the voltage wouldtell the actuator to go one way,and the absence would tell it togo the other way.

This does not, however,allow us to stop the actuator atan intermediate position. Inorder to do that, we need threepairs of wires onto which wewould apply a voltage signal tothe first pair to tell the actuatorto go “Open,” the second pairto tell the actuator to go“Closed,” and the third pairwould tell the actuator to “Stop.”

This basic control gives usthe power to move the actuatorfrom a remote position, suchas from the control room.However, should the distancefrom the control room to theactuator be significant, then wewould probably want to apply aDC control signal so that whenwe remove a control signal,there is no residual voltage dueto capacitance, which coulddelay the removal of the signalat the actuator. For that rea-son, long distance control is

If phase reversal occurs, a bentstem (pictured above) can result.Rotork’s Syncrophase featureprevents this from happening.

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often achieved with a directcurrent signal.

As yet we have only dis-cussed how to tell the actuatorto move, we have not exam-ined the means of confirmingthat the actuator is in thedesired position. Both electricand fluid power actuators areequipped with position indicat-ing switches that trip at theends-of-travel. We can there-fore run another two pairs ofwires to the actuator – one togive us “Fully Open” indication,and the other to give us “FullyClosed” indication.

If continuous positionindication is required, then acontinuous position transmittercould be fitted to the actuatorusing two or three wires so thata 4-20 mA position indicatingsignal is received at the controlroom. We now have ten controland indication wires runningfrom the control room to eachactuator to give us “Open,”“Stop,” and “Close” control, and“Open” and “Closed” or “Con-tinuous Position” indication.2. Modulating Control.

If the requirement is tohave the actuator positioned atsome intermediate position soa process is controlled, then apositioning type of control isrequired. There are fundamen-tally two types of positioningcontrols; the first uses intelli-gence in the actuator, and the

second uses intelligence in thecontrol room. In the first in-stance, a position controller isplaced in the actuator. In thiscase, when a 4-20 mA posi-tioning signal is transmittedfrom the control room to theactuator, it positions the valvein proportion to the signal. Forexample, a 12 mA signal wouldposition the valve in the “Mid”position.

The second type of controluses a PLC or other hostcomputing device to energizethe actuator “Open” or “Close”control until the desired posi-tion feedback is received fromthe actuator via the continuousposition transmitter.

In the first option where theactuator has its own positioner,the movement of the actuatorcan be restricted using a built-in time delay and dead bandcontrols. For this reason,standard type actuators can beused for positioning duty;however, for constantly modu-lating duty, special modulatingactuators are available (IQM,AQM, and so forth).3. Digital CommunicationSystems.

The previously describedcontrols function perfectly well,but, because of the length ofcabling required to connectactuators to the control room,the cost of cabling, conduit, andlabor can be astronomical. A

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simpler method of connectingactuators to the control roomuses Rotork’s Pakscan technol-ogy which consists of a signalgenerating master station thatcommunicates over a two-wireshielded twisted pair loop to fieldunits located inside of theactuators around the plant.

The master station gener-ates digital signals which areaddressable to each actuator, soeach or every actuator can becommanded to “Open,” “Close,”or go to any position. Over thesame two wires, actuatorposition can be reported back tothe master station for each ofthe actuators.

Two-wire control canperform all of the functions ofthe standard hard-wire control,and enables the examinationand communication of addi-tional information in eachactuator over the two-wireloop. For example, the statusof the following can all bebrought back over the two-wireloop:• Torque Switch• Limit Switch• Thermostat• Local/Remote Controls• Contactors• Power Supply.

In addition, the masterstation can check every actua-tor every few seconds toensure its availability foroperation. This is the scanning

part of the Pakscan system.Should a break occur in the

two-wire loop, then the masterstation immediately detects thefault and reconfigures the loopinto two branches. This givesthe Pakscan system singlefault tolerance.

The Pakscan master stationconnects to the host controlcomputer via an RS-485 or RS-232 Modbus RTU link. Thisenables the programmer tohave a proven interface be-tween his host computer andthe Pakscan equipment. RotorkPakscan systems have beensuccessfully interfaced with all ofthe major international DCS andPLC manufacturers.4. Stand-alone Control Intelli-gence.

If no host computer orintelligent control devices areused, then Rotork can providetwo methods of intelligentcontrol. The first is ourPakscan IIS master station,which has inherent program-mability enabling sequencesand interlocks to bepreprogrammed in the masterstation. These sequences canbe initialized using push but-tons mounted on the face ofthe master station.

Because the master stationis watertight, it can be locatedin operational areas, so thatvisual monitoring of the pro-cess can take place while

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standing at the master stationcontrolling the process. The IISmaster station can also belinked to a host computer viaan RS-232 or RS-485 ModbusRTU link.

The other control option isto utilize a standard IBM-compatible PC with Rotork’sPakVision software. Thissoftware allows for control ofindividual actuators, program-mable sequences, and pro-grammable interlocks, as wellas a visual display using mimicdiagrams of the actuators inthe plant. Record-keeping logsare also part of the software totrack operator actions, changesin the plant equipment, andalarms.5. Startup and Commissioning

of Control Systems.The first step in commis-

sioning a remote controlsystem for the Rotork actuatorsis to locally commission theactuator to ensure correctfunctionality at the automatedvalve. Only then should remotecontrol commissioning take place.

For conventional hardwiredsystems, functionality of eachcontrol and position feedbackshould be checked sequentially,preferably with a technician atthe valve and a technician in thecontrol room to initiate andconfirm control commands. Inthe event of a problem, then thecontinuity of the wiring andwiring connections should besystematically checked, as wellas the functioning of control and

The Pakscan IIS master station is water-tight and can be located indoorsor outdoors.

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indicating switches.Commissioning a Pakscan

system fortunately is signifi-cantly less complex. After thecommissioning of each valvelocally, the continuity of the two-wire loop should be checked.Because it is a “daisy chain,” theloop is a relatively straightfor-ward check compared to a multi-strand hard-wire system.

Because the Pakscan IIEand IIS master stations arestand-alone communicationdevices, there is no need tohave PLC or DCS host con-nections made in order tocommission the system. Usingthe keypad on the front of themaster station, each valve canbe addressed sequentially andthe operation and communica-tions checked, again preferablywith a technician located at thevalve itself.

The master station has adiagnostics capability, so faultscan be specifically identified inthe control room.

Once the host DCS isconnected to the masterstation, the incoming signalsfrom the host can be monitoredat the master station for com-plete diagnostics.

However, if the masterstation has previously beenused to commission the loop,then faults should be confinedto software commands andresponses.

SUMMARYToday’s automated valve

actuators and two-wire com-munication systems can becost-effectively installed andretrofitted in virtually any typeof facility. Automated valveoperation provides an array ofimportant benefits, including:• increased plant effeciency• decreased labor costs• improved safety• more effective control• the flexibility to add additional

monitors and alarms• less chance of operator error• less risk of injury to personnel• increased environmental

protection, and more.Most important, even very

old and small plants can enjoythese benefits by retrofitting.

In fact, today’s valve actua-tor technology is so affordableand dependable that manualoperation is fast becomingoutdated and is relevant for onlya few types of applications.FOR MORE INFORMATION

For more information, contact:Mr. Chris WarnettRotork Controls, Inc.19 Jet View DriveRochester, NY 14624 U.S.A.Telephone: 716-328-1550Fax: 716-328-5848Email: info@rotork.com

Rotork’s website address ishttp://www.rotork.com , whichcan be accessed 24 hours aday.

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IQ Multi-turn 3-phase(eg., Gate or Globe Valves)10 to 2,200 ft. lbs. torque

IQM Multi-turn 3-phaseModulating (eg., Gate or Globe Valves)

10 to 200 ft. lbs. torque

A Multi-turn 3-phase, 1-phase, and DC(eg., Gate or Globe Valves)10 to 2,200 ft. lbs. torque

A or IQ 3-phasewith IB or IS Gearboxes (eg., Gate or Globe Valves)Multi-turn 12 to 24,000 ft. lbs. torque

A or IQ 3-phasewith IW Gearboxes (eg., Ball, Butterfly, or Plug Valves)Quarter-turn 288 to 100,000 ft. lbs. torque

AQ Quarter-turn 3-phase, 1-phase, and DC(eg., Ball, Butterfly, or Plug Valves)40 to 800 ft. lbs. torque

AQM Quarter-turn 3-phase, 1-phase, and DCModulating (eg., Ball, Butterfly, or Plug Valves)

40 to 800 ft. lbs. torque

Q Quarter-turn 1-phase(eg., Ball, Butterfly, or Plug Valves)40 to 300 ft. lbs. torque

G Multi-turn 3-phase(eg., Gate or Globe Valves)1,200 to 5,000 ft. lbs. torque

AppendixRotork Actuator Selection Matrix – Electric

Electric Actuators Description

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P – Quarter-turn 40 to 250 psi, air, gas, hydraulic, water(eg., Ball, Butterfly, or Plug Valves)2,680 to 2,000,000 in. lbs. torque

SP – Quarter-turn 40 to 250 psi, air, gas, hydraulic(eg., Ball, Butterfly, or Plug Valves)655 to 5,090 in. lbs. torque

PAW – Multi-turn 80 psi, air or gas(eg., Gate or Globe Valves)16 to 300 in. lbs. torque

PAW/IW – Quarter-turn 80 psi, air or gas(eg., Ball, Butterfly, or Plug Valves)Torque on application

PL – Linear 40 to 250 psi, air or gas(eg., Gate or Globe Valves)Thrust on application

H – Quarter-turn 250 to 3,000 psi, hydraulic(eg., Ball, Butterfly, or Plug Valves)1,215 to 2,000,000 in. lbs. torque

HPG – Quarter-turn 250 to 3,000 psi, gas(eg., Ball, Butterfly, or Plug Valves)2,680 to 2,000,000 in. lbs. torque

HPL – Linear 250 to 3,000 psi, air or gas(eg., Gate or Globe Valves)Thrust on application

R – Quarter-turn 20 to 125 psi, air or gas(eg., Ball, Butterfly, or Plug Valves)45 to 10,500 in. lbs. torque

Fluid Power Actuators Description

AppendixRotork Actuator Selection Matrix – Fluid Power