Power Pumping

Pump Rebuilding andBalancing (Part Two)Dawn Hines and Robin DeRousse, Hines lndustries, lnc. and Jerzy Moszynski, MMS ANSIFLO Pump

The conclusion of a two-part article on the tricks of the trade for pump rebuildingand balancing, featuring a case study on a boiler feedwater pump.

T\ umps are sent to rebuilding| -' and remanufacturing com-

I panies because buying newcan be expensive and require longlead times. For instance, a 39 indiameter, 1,000 lb bronze impel-ler may cost $Z8,OO0 and takemany weeks to deliver. In thesecases, the impellers involved in anoverhaul are often built back upto the required specifications andrebalanced.

In one particular instance, apump rebuilder received an urgentrequest to repair a damaged boilerfeed water pump. Boiler feedwater pumps are expensive, complex, precision machines withlong lead times. The customer's operation was down due to thepump failure, and it was costing thousands per d^y.

The first step upon receiving the damaged pump was toanalyze the condition of the components, considering bothcosts and lead times for replacement parts versus remanufactur-ing or reusing existing components. The machine was cleanedand its parts sandblasted before it was inspected. The damagedpump's system was also analyzed.

During initial inspection, the pump shop discovered thatthe impeller was worn, and the walls on one side were thin fromprevious repairs and balancing. Because of the long lead timefor impeller replacement and the urgent nature of the case , thepump rebuilder carefully analyzedwhich parts were salvageableand could be safely reused or repaired to acceptable standards.

Pump shafts and impellers can often be reused, but thispump impeller had thin cross-sections in areas that had beenbalanced in the past. Spray welding was used to build up thematerial. During the last five to 10 years, welding has become asolution, even for severely damaged impellers. Methods include

nickel welding for iron impellersand spray welding techniques.

RebuildingAfter questionable areas had beenbuilt back up, the impeller wasrebalanced by removing weight,according to a complete set of pro-cedures that the pump companyfollows to ensure a satisfactoryoverhaul:1. Ensure absolute cleanliness for

the power ends of pumps2. Measure shaft runout to check

if runout is within allowablelimits (i..., normally 0.002 inat stuffing boxes)

3. Provide a new shaft if necessary4. Balance the shaft first5. Build a mandrel for each individual impeller-the

rebuilder balances all components on mandrels to ensuretrue running

6. Balance each impeller individually for mulristase machin-ery, then stack and balance the entire assemblr-

7. Make certain the user has examined the possibiliry ofproblems with the motor since a larqe amount of pumpfailures can be attributed to the driver

8. Complete balance certification documentation

Every pump that passes through the rebuilder's operationis balanced because pumps are rotating machines. Balancingprevents vibration, improves performance, increases the meantime bet'ween maintenance, avoids deflection and preventsshaft breakage and bearing seal problems. The smoother a pieceof machinery runs, along with correct lubrication practices and

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50 DECEMBER 2oo9 www.pump-zone.com PUMPS & SYSTEMS

lmportant Features in Balancing Machines for Pumps. Pure unbalance readirg.Tooling and balancing mandrels always have some

amount of inherent eccentricity and unbalance. Be sure balancing machinesofrware automatically zeroes out the error caused by tooling unbdance andeccentriciry, to deliver a true reading of impeller unbalance.

. Sofrware for Pump Balancing. Sofrrvare should include features to:1. Account for keys and keyways2. Determine the proper ISO balance tolerance based on the part weight and

usage RPM3. Vector the unbalance into two veins, blades or segments

. Accurary and Speed. Accurate reading of arnount and angle of unbalance inboth single plane and two planes is critical for fast, efficient correction. If theoperator removes the amount of material at the angle specified in the firstreading, the part should be balanced on the first spin.

other factors, the longer its useful life will be. Bearings andmechanical seals are rypically the weak links in the chain. Theless vibration, the longer these parts will perform at acceptablelevels.

The assemblies must be as closely balanced as is practi-cal to offset other problems that may develop in a pumpingsystem. Standards developed by various organizations forpump/motor repairs form the basic guidelines for acceptablemachine overhauls.

Standards boards in the pump indus-try include ANSI (American NationalStandards Institute), Hydraulic Institute,ASME (American Soci.ry of MechanicalEngineers) and the American PetroleumInstitute. They have created and main-tain standards for the remanufactureand repair of both electric motors andpumps.

Pump Replication toReduce DowntimeThe rebuilder proposed that the cus-tomer have one machine running andone spare for the future, along with therequired parts on the shelf, to avoiddou'ntime when a pump shuts down orrequires periodic maintenance. tVhen a

catastrophic failure occurs and there is aneed for parts that fall into the long leadtime items category, it is then necessaryto repair or remanufacture the used partsavailable on hand.

"All pumps are theoretically engi-neered products, so pump and part leadtimes tend to be long. This requiresrebuilders to have accurate knowledge as

to the application of pumping machineryin order to duplicate the performance of aspecific pump during any overhauls, sinceany inaccuracies can dramatically affect theperformance of a machine," states JerzyMoszynski, president of MMS ANSIFLOPump.

GonclusionPump failures are costly. Balancing and astraight shaft are essential to increasing thetime berween failures, both for new andrebuilt pump systems. After the system isinstalled, proper maintenance and afien-tion to resonance levels is the k.y to longpump life.

P&SDawn Hines is CEO and. Robin DeRousse is a sales engi- I;:;;;:.r,:::;"1;*;l::;-':''

Phone: 734-76e-23 oo'

IJerzy Moszynski is president of MMS ANSIFLO Pump, IPhone: 435-843-4256, mmsinc@worldnet.att.net. I

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PUMPS & SYSTEMS www.pump-zone.com DECEMBER 2OO9 51