rotary pump startups

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Rotary Pump

Startups A pre-startup guide that will help keep gremlins away from your system.By James R. Brennan

Many pump startupsare the culmination of months if not yearsof work designing the process, machine orsystem, specifying components,instrumentation, protective devices, andreviewing and qualifying suppliers. It isalso the most vulnerable time for anypump. This article describes cautions,reviews and inspections that should beconducted before startup to help insurethat all those many gremlins of pumpingsystems are found out and eliminated intime.

Thoroughly read the technicalmanuals and instructions from the pump,driver and all auxiliary equipmentsuppliers to learn of requirements that maybe specific to their equipment design.While this is the easiest method to protectthe system, it is overlooked more oftenthan not.

PIPE AND VALVESPiping and valving installation

(Figure 1) should probably be consideredfirst.

Be sure all required valves havebeen installed. Verify that none is installedbackwards. An absent or reverse mountedcheck valve, foot valve or relief valve cancause very serious damage. Piping shouldhave been inspected during fabrication toinsure that weld bead, weld rod and scalehave been completely removed. Such hardparticles can cause catastrophic pumpfailure should they lodge in the wrongpump clearance. Temporary, if notpermanent, pump inlet strainers should beconsidered if not present. They should

start in a clean condition so thataccumulation of dirt can be monitored.

The piping system should bepressure tested. Avoid imposing on anysystem component pressures in excess of its design limits. Many pumps canwithstand discharge pressure only on theirdischarge side.Inlet piping systems are frequentlysuitable only for low pressure. Thepressure test medium should becompatible with the components/ systemto be tested. Don't use water if the system

is not a water system. A low pressure (15psig, 1 Bar g) compressed air test may beadequate to find missing flange gaskets orother obvious leak sources.

Check and tighten all flange bolts tospecified torque. Pump inlet and dischargepiping should have been made up from thepump for a distance of perhaps 20 ft (6meters) to minimize pipe strain on thepump. Piping should be independentlysupported. Close internal clearance pos-itive displacement rotary pumps do notmake very good pipe anchors. When pipeflanges are unbolted from the pump, flangebolts should be able to beinstalled/removed without forcing pipinginto position. There should be a flange-to-pump gap not exceeding the greater of twice the flange gasket thickness or 1/16"(3 mm). If the gap is greater than either of these values, rework the piping until thegap is this width or less.

Positive displacement pumps will

normally have a system pressure relief valve installed from the discharge piping toeither the source of the pumped liquid,such as a supply tank, or to the pump inletpiping (a less desirable point due to thepotential for temperature buildup duringrelief valve operation). This valve willusually be set slightly higher than themaximum anticipated normal systemoperating pressure. If possible, verify thatit has been properly set. If this cannot beverified, consider adjusting the relief valveto a very low pressure and changing itupward after pump startup. Consult relief valve vendor's technical data to be surevalve adjustment is done in the correct (tolower pressure) direction.

Ideally, the entire piping and valvesystem will be thoroughly flushed toremove all dirt and fabrcation debris. Thisis customarily done using a flush pump -not the normal system pump. Strainers andor filters are installed at appropriatelocations, and their dirt accumulation ismonitored until they show no accumulationfor a period of 24 hours. Flushing usuallyuses light, fairly hot (150 ° F, 65 ° C) oildelivered



at flow rates higher than system design.The higher flow rates cause higher liquidvelocities within the piping system and aremore likely to dislodge debris. Somesystems will use vibration equipment toimpose mechanical "shaking" on the

piping, again to maximize the dislodgingof dirt. Very extensive piping systemshave been known to show debrisaccumulation even after 30 days of flushing. Because of their long distancesand relatively huge holding volumes,pipeline systems will frequently use"pigs," bullet shaped devices, sometimesequipped with wire bristles, which arepropelled ahead of a flush or initialproduct batch of liquid to scrub debris anddirt from the inside of the pipe.

Before final startup, be sure valvesare open or closed as required. Pump inletand discharge valves are normally leftfully open. Manual pump bypass valvesare also normally left open on startup. Anair bleed valve in the discharge piping at ahigh point near the pump will significantlyimprove the pump's ability to self prime.The valve is left open during startup untilliquid flows. It is then shut. Be sure toknow where this flow will be directed toavoid inadvertent discharge to atmosphereor spillage. Steam turbine steam valving isvery important. Turbine startup proce-dures should be thoroughly reviewed asthere are personal injury issues associatedwith this equipment if it is started oroperated improperly.

FOUNDATEON, ALIGNMENT ANDROTATION

If horizontal pumps are used, be surethe foundation is level, that hold-downbolts are tight and that grouting, if used,has completely filled the baseplate (nohollows or voids) and has cured. If thepump will be handling liquid above about1500F (65 0C) or a steam turbine is used asthe driver, an estimate of the centerlinegrowth in height of the hot machine mustbe made. Shaft to shaft alignment (cold)should incorporate a deliberate,compensating offset, so that alignment is

more nearly correct when equipment is upto operating temperature. Coefficients of thermal expansion for common pump casematerials are provided in Table 1.

The coefficient is applied to thecenterline height of the shafts and the difference in tem-perature between that at which the unitwas aligned and temperature of expectedoperation. The cold machine should be

shimmed high by this calculated amount.The purpose of any shaft aligning

procedure is to align the centers

of the machine shafts with each other, NOTto align the flexible coupling hubs. Attemperature, alignment should be within0.003 inches (0.076 mm) Total IndicatorReading (TIR), both angular and parallel.Consult a good aligning procedure to

achieve or verify this degree of precision.The fact that the coupling may be rated to amuch greater misalignment capability hasnothing to do with the shaft-to-shaftalignment of the equipment. Survival andlongevity of the machinery, NOT the cou-pling, are the objectives. If hot pumpsand/or drivers are used, after they are atnominal operating temperature long enoughfor thermal growth to have stabilized(probably one hour or more), shut down theequipment and verify that alignment iswithin prescribed limits.

Never rely on the alignment that wasproduced where the pump and drive trainwere assembled. Transportation, lifting andhandling as well as foundationirregularities will impact alignment, alwaysin an undesirable direction. Final align-ment should be achieved as nearly the laststep before actual starting of the pump. If equipment is to be dowelled in place, do soto the pump ONLY after several hours, if not days, of good operation and hotalignment checks.



The use of resilient mounts issometimes desirable to reduce vibrationbeing transmitted into the underlyingfoundation. If used, such mounts must notbe deployed beneath the pump or driverbut between the pump/driver baseplate or

bracket and the foundation. The pump anddriver must be rigidly aligned, notresiliently aligned, since the resilientmounts will not maintain adequatealignment under torsional reactions fromthe transmitted torque.

Direction of rotation is critical formost equipment. It is usually indicated byarrow nameplates. Remember that somegearing will reverse rotation from inputshaft to output shaft. Most engines and tur-bines must be purchased for a specificdirection of rotation. This is also true of most pumps. Standard AC electric motorsare frequently bi-drectional; their directionof rotation will depend upon how thepower cables are connected. It is normallynot possible to predict their direction of rotation before- hand. It is recommendedthat the flexible coupling at the motor shaftbe disconnected and the motormomentarily energized (jogged on, thenimmediately off) to see if its rotation iscorrect for the rest of the drivenequipment. If not, two of the electricpower cables will need to have theirconnections reversed. Verify correctrotation after reversing, if necessary,before re-engaging the flexible coupling.

LUBRICATION

A person should be able to turn overalmost all rotary pumps by hand. Pumpsshould generally turn over smoothly, with

no catches or uneven rubbing. Very largepumps may need a helper bar but shouldnot be at all difficult to turn. If one is,consult the pump vendor Partialdisassembly may be advisable todetermine the cause of difficultyencountered (foreign material, pipe strain,rust) before starting.

STARTUP SPARES

With care and planning, startups willgenerally go smoothly, without significantproblems. However, it is prudent to havekey spareparts on hand in the event they are needed

quickly for correction after someunanticipated problem, minor damage, orneed to disassemble a piece of equipment

for inspection. For rotary pumps thiswould normally be a set of shaft seals,gaskets, o-rings and bearings, frequentlyavailable as a minor repair kit. For otherrotating equipment, spare bearings, greaseand oil seals and gaskets should be onhand so as to avoid delay in the startup.More extensive spares will depend onavailability from the vendor, criticality of pump operation, plant practice and,perhaps, other issues specific to theinstallation. If the startup goes well and thespares are not consumed, it is appropriateto

Most rotating machinery has some form of lubrication for its bearing systems (Figure 2).It may be as simple as a permanently greasepacked, sealed ball bearing or as complicatedas a separate lubricating oil pump systemcomplete with cooler, filter andinstrumentation. Be sure to verify that anylubrication required has been addressed.Equipment that has been in storage mayrequire draining and addition of freshlubricant or even flushing out. Any gearingpresent (pump timing gears or reduction drivegears, for example) should be reviewed for

the presence of the correct type and quantityof lubricant. Constant level oilers should befilled to their mark with clean, fresh lubricantof the correct type. Some flexible couplingsare grease lubricated and should also bechecked. Most electric motors will havegrease lubricated antifriction bearings thatshould be checked as well.



pump and as much of the inlet pipingsystem as possible with the liquid to bepumped. This will assist in priming andreduce the risk of pump damage during anotherwise dry start. A rotary pump willprime more quickly if internal pumping

elements are at least wetted. Priming isnothing more than pumping air from theinlet system to the discharge system. Theability of a rotary positive displacementpump to act as an air compressor is verymuch related to having some liquid presentinternally.

Pump shaft seals, especially mechanicalseals, should never be operated dry.Immediate, or at best premature, sealfailure is the inevitable result. Again, fillingthe

keep them on hand for future routineinspections and service.

RESOURCES

Be sure electric power, steam,cooling water, hot oil, instrumentationpower or air or any other auxiliaryresources are available and ready beforestart. Be sure adequate pressure andtemperature gages are in place soobservations can be made during startup.Without them, you are working blind.

Speed indication (tachometers) may also

be needed if the drive is not a fixed speedone such as an AC electric motor. If the

pump will be handling hot liquid, preheatthe pump as necessary so it is not exposedto thermal shock when otherwise hotliquid reaches an ambient temperaturepump. Rotary pumps may be somewhatmore sensitive to thermal shock due totheir close internal running clearances .

LAST MINUTE

It is good practice to fill thepump with the liquid to be pumped and

hand rotating the pump a few times helpsinsure that liquid is present at the shaft

sealing mechanism to carry awayfrictional heat during startup. If theparticular pump has a seal chamber accessplug, remove the plug, fill the chamberwith liquid and reinstall the plug.

Have phone numbers on hand of keyvendor service departments, fire brigadeand medical emergency services in theevent they are needed. When handlingpetroleum and other flammable liquids,there are both



pollution and fire hazards present.Insure that there is an adequate

supply of liquid in the pump inlet system(no half empty supply oil tanks or thelike). It is also prudent to confirm wherepump discharge flow will be going to be

sure the discharge system is ready.Loud or erratic noise at startup is anindication of cavitation (inadequate pumpinlet pressure) or air being drawn into thepump inlet system. It is frequentlyaccompanied by increases in or excessivevibration. If mild, troubleshoot the cause.If severe, shut down the pump and find thesource of the problem.

Use the Rotary Pump Startup Check List accompanying this articleor a similar control to help insure that allcontingencies have been addressed.

CONCLUSION

Our discussion cannot be con-sidered all-inclusive since each pumpingsystem has unique features andrequirements, some of which may interactwith each other or with other aspects of the overall plant operation. In addition, noallowance has been made here forregulatory requirements, specializedindustry or company guidelines and thelike. Where values are recommended, theyare intended for use in the absence of vendor or specifically engineered informa-tion. Always use the more stringent of either the recommendations herein or thevendor or engineering guidelines. E

James R. Brennan, currently groupmanager for three pump divisions of Imo

Industries specializing in crude oil trans- port pumps, is a 1973 MIE graduate of Drexel University, Philadelphia, PA, USA. He has more than 25 years of experiencewith screw pumps at Imo Industries, is amember of the Society of Petroleum

Engineers, and was engineering manager of a pump division for five years. He hasauthored many papers and articles as wellas spoken at a number of industryconferences. He is also a frequent contributor to Pumps and Systems.

Reprinted from the March Issue of:PUMPS and SYSTEMSThe Magazine for Pump UsersMarch 1996

rotary pump startups

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