MAINTENANCE AND TROUBLE-SHOOTING OF

CENTRIFUGAL PUMPS

NAMITHA M R2015664502

MAINTENANCE OF CENTRIFUGAL PUMPS

Proper maintenance of a CF pump is important

to ensure its trouble-free and long service

The maintenance operations of CF pump

includes:

1. Routine Preventive Maintenance

2. Overhaul or Repair operations

1. ROUTINE MAINTENANCE

Performance of the pump should be observed daily

Any abnormalities in operation should be taken care

of promptly

The alignment of the pump unit should be checked

occasionally

Bearings should be lubricated regularly

Half-yearly Maintenance

Pumps installed on cavity wells need half yearly

checking

Shaft packing is checked by observing the leakage

from it

Leakage from the stuffing box is excessive or the

packing is worn entire packing in the box will

have to be replaced

CONTD…

Overhauling of stuffing box All the old packing

rings are removed and interior of stuffing box is

cleaned thoroughly

Shaft and shaft sleeve surface are properly

cleaned before inserting the packing rings

CONTD…

If shaft sleeve is badly worn or scored, it is replaced

Straightness of the shaft should be ensured

Radial clearance between the shaft and the stuffing

box bore is measured

Packing ring shouldn’t be inserted in a spiral form

CONTD…

Packing rings are fitted carefully:

o Open them radially until the ends are wide apart as

1/2 the shaft dia. the ends are turned apart in an

axial direction slide the rings over the shaft each

ring is pushed in to the stuffing box, inserting the

joint first

o The joints of succeeding packing rings should be

staggered

CONTD…

Assemble the gland ring and tighten the nuts by

hands or using a spanner

When the pump is in operation, the nuts are

again adjusted to achieve the desired leakage

from the stuffing box

If decrease in discharge is found, the pump is

opened and cleaned

2.OVERHAULING OF PUMPS

Most overhaul work of CF pumps is concerned

with the rotating parts

Overhauled annually or once in 2 years

In many situations, the operating conditions don't

permit annual shutdown periods for overhaul

CONTD…

Situations call for a shutdown of the pumping

plant for trouble shooting, repair and possible

overhaul:

Fall-off in pump performance

Excessive noise during pump operation

Excessive vibration of pump

Symptoms of corrosion or erosion trouble

a) Dismantling of CF pumps

o Pump has to be dismantled for overhauling

o Pump is first disconnected from the piping

system

o Steps involved in dismantling a belt driven pump:

1. Remove the inlet and outlet flanges

2. Remove the bearing cap by removing the bolts

holding it

3. Remove the grease cup and bearing lock nut

CONTD…

4. Remove the pedestal and take out the ball

bearing, using a bearing puller

5. Remove the belt shifter

6. Remove the nuts and bolts joining the casings

and remove the casing slowly, taking care not to

damage the impeller and casing rings

7. Remove the impeller nut

CONTD…

8. Dismantle the rotating unit and remove the

impeller slowly by hammering back the shaft

gently, using a wooden block

9. Remove the impeller from the rotating unit

10. Remove the pulleys using a pulley puller

11. Dismantle the stuffing box

b) Overhauling of impellers

o The eye, vanes, shrouds, wearing rings, passages

and hubs are checked

o Corrosion, cavitation and erosion are accompanied

by the wearing of the impeller vane surfaces

o Corrosion is due to warp or holes in the thinned

surfaces

o Impeller have to be replaced, if cavitation is severe

o Impeller have to be thoroughly cleaned before

inspection

c) Balancing of impeller

o Badly worn or corroded impeller needs

rebalancement

o Balancing of an impeller can be checked by

pressing it on an arbor, the ends of which rest on

2 parallel and level knife-edges, by hand

o If found unbalanced, the metal is removed from

the heavy side

d) Repair of shaft

o Shaft is checked for bending with a dial gauge, by

turning the shaft between lathe centres

o If shaft is badly bent, it should be returned to the

manufacturer

o Reconditioning of the shaft will require welding or

metalling, followed by rough finishing cuts

o Final finishing is done by filing

e) Replacing of wearing rings

o Proper clearance of the wearing ring is important

o Increase in clearance results in leakage which

decreases efficiency

o If wearing rings are worn out, they have to be

replaced

f) Repair of shaft sleeves

o Shaft sleeves often get worn out when packed too

tightly

o Reconditioned by welding or metalizing, followed

by a rough finishing cut

o If wear is excessive, shaft sleeves have to be

replaced

g) Repair of Non-stationary Components

o Repair is negligible

o Bed plate is kept clean of grease and oil at regular

intervals

o Joints and piping are checked regularly for leakage

o Foundations are kept clean

o Cracks in foundations are repaired in time

o Surface of casing is painted

h) Reassembling the parts of a CF pump

o Steps involved are:

1. Mount the pulleys on the shaft

2. Mount the casing and stuffing box bushes on the

shaft

3. Gently mount the impeller on the shaft

4. Insert the impeller key carefully

5. Adjust the impeller at its correct position and

tighten the impeller unit

CONTD…

6. Insert the gasket and grease it properly

7. Mount the casing by tightening its nuts and bolts

8. Insert the belt shifter at its correct position

9. Insert the shaft sleeve and tighten it properly

10. Mount the pedestal and align it properly by

inserting the desired packing (shims)

CONTD…

11. Mount the ball bearing, on hand press, and

tighten the bearing locking nut. Do not hammer

the ball bearing

12. Mount the bearing cap

3. TROUBLE-SHOOTING IN CF PUMPS

Troubles are of 3 types: mechanical, hydraulic and

driver related

Mechanical troubles: Breakage of coupling or

shaft

Hydraulic troubles: Failure to deliver water,

reduction in discharge and over loading of the

prime mover

a) No liquid delivered

o Lack of prime

o Speed of electric motor or engine too low

o Discharge head too high

o Suction lift too high

o Impeller plugged

o Vapor lock in suction line

b) Not enough water delivered

o Air leaks

o Worn wearing rings

o Damaged impeller

o Defective foot valve

o Worn gaskets

o Impeller eye too small

c) Pump losses prime after starting

d) Overloading of Motor / Engine

o Low discharge head

o Packing too tight

o Bent shaft

o Distorted casing

o Pump speed too high

e) Overheating of stuffing box

f) Excessive vibrations

g) Overheating of bearings

h) Rapid wear of bearings

THANK U!!!