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OVERHAULING CLARIFIER SUPPLY PUMP(1-BRAVO)

Reviewed By:Yusaf Razi

Clarifier supply pump at LalPir is a doublesuction volute pump, having its suction port anddelivery port in the same horizontal plane. Thepump is designed such that it can be divided inits horizontal plane containing shaft center intotwo parts so as to facilitate disassembly andreassembly work without disconnecting the bothsuction and discharge pipelines. The pumpsmotor is controlled by a VFD and is the mostused of the three pumps. Hence a completeoverhaul of the pump to ensure maximumrunning time without failure is economically

viable.

The impeller of the pump had undergone pitting,and hence had to be replaced. Other majorcomponents of the pump were replaced as welland the list of those components is shownbelow.

The radial clearance between the casing wear ringand impeller need to be adjusted to allow propersealing without the two of them making contact

with each other. The design diametrical clearance

needs to be 0.5-0.6mm. We installed the impelleronto the shaft and let the wear rings rest on it.

Then using a feeler gauge, we checked for theclearance between the impeller and the wearingat the bottom. This reading came out to be0.5mm (diametrical). The wear ring was slightlymachined to increase the clearance to 0.6mm.

Once the radial clearances were adjusted, the

rotor was assembled in MMD workshop, then

taken to the site. The rotor was lifted and placed

on top of the pump lower housing.

Figure 1 Pitting on Previous Impeller

Figure 2 Old Pump Rotor

Figure 3 Determining Radial Clearance

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The casing halves, bearing housings, coupling hubs and other components were thoroughly

cleaned. The area which supports the casing wear ring was cleaned using a scrapper to aid the wear

ring in setting properly. To center the shaft on the pump casing, bearings were used. The bearings

were heated to 110oC using bearing heater to allow them to press fit on the shaft. As the bearings

sit on their respective position in the bearing housing, the shaft aligns itself axially on the pump.

After the shaft was axially positioned, the impeller was aligned centrally inside the volute casing

using the shaft nuts (slacking on one side and tightening it the other). It was made sure that the

gap between the impeller and the wall of the volute is same on either sides of the impeller. Once

the impeller was in center, the shaft nuts were secured in position using the grub screws.

The radial clearances were verified after placement of the rotor. The pumps upper half was lifted

and placed on top of lower half. This was done in order to check for free rotation of the pump

rotor. In the first attempt, the rotation of the rotor did not occur easily using hands. This was

because of the contact formed between the casing wear ring and the impeller wear ring. To rectify

the problem, the pump casings area where the wear ring settles was thoroughlycleaned again with

a scrapper to make sure the wear ring does not touch the impeller and seize it when the casingsupper half is placed. After fixing the issue, the upper casing was finally placed on top.

Once the pump was assembled, the coupling hub

was installed on the shaft on the pump. The

coupling gap between the pump and motor was

small, hence the motor had to be lifted and

moved away before the coupling hub could be

slid on to the shaft. The coupling hub was heated

to 200oC. Finally the alignment was performed

between the pump and motor shaft.

Figure 4 (Left) Installation of Rotor (Right) Central Aligning of the Impeller

Figure 5 Placing Top Casing Figure 6 Packing

Figure 7 Alignment in Progress

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Pump/Motor Shaft Alignment

Date & Time = 12thDec, 2013, 10:00 am

9 Oclock = 0.02 mm 3 Oclock = -0.01 mm

6 Oclock = 0.01 mm

12 Oclock = 0.00 mm

9 Oclock = -0.01 mm 3 Oclock = -0.01 mm

6 Oclock = -0.02 mm

12 Oclock = 0.00 mm

Figure 8 Radial Alignment

Figure 9 Axial Alignment