Question 1

Why is my centrifugal pump producing no flow or discharge?

Accepted Answer

Primary causes: pump not primed, impeller rotating in reverse direction, suction lift too high. Solutions: vent casing and fill suction line completely, swap two electrical supply phases to reverse rotation, recalculate NPSHA and lower pump elevation.

Question 2

Why is my pump producing low flow or reduced capacity?

Accepted Answer

Primary causes: clogged suction strainer, worn impeller wear rings, air leaks in suction line. Solutions: inspect and clean strainer, measure clearances and replace wear rings if worn, seal all joints and verify flange gaskets.

Question 3

Why does my pump lose prime after startup?

Accepted Answer

Primary causes: air pockets in suction pipe due to concentric reducer, faulty foot valve, vortexing at suction source. Solutions: replace concentric reducer with eccentric reducer flat-side up, inspect and replace foot valve, increase submergence depth in supply tank.

Question 4

What causes pump cavitation and how do I fix it?

Accepted Answer

Primary causes: NPSHA lower than NPSHR, high fluid temperature raising vapour pressure. Solutions: raise fluid source level or increase suction pipe diameter to reduce friction losses, cool fluid prior to pumping. A gravel-like noise from the pump casing is the primary symptom.

Question 5

Why is my mechanical seal leaking?

Accepted Answer

Primary causes: dry running causing thermal shock to seal faces, abrasives scoring seal faces, shaft deflection from misalignment. Solutions: install dry-run protection relay, add cyclone separator to seal flush line, realign pump and motor shafts with dial indicators.

Question 6

What causes excessive pump vibration?

Accepted Answer

Primary causes: shaft misalignment, impeller imbalance, soft foot under baseplate. Solutions: realign using reverse dial indicator method, dynamically balance impeller, shim baseplate to eliminate rocking.

Question 7

What causes excessive pump noise?

Accepted Answer

Primary causes: bearing failure, cavitation, coupling insert wear. Solutions: replace bearings and verify lubrication type and quantity, address NPSH deficiency, inspect flexible coupling insert for deterioration and replace.

Question 8

Why is my pump overheating?

Accepted Answer

Primary causes: operating below minimum continuous safe flow (MCSF), closed discharge valve. Solutions: open bypass line to maintain minimum flow, gradually open discharge sluice valve to operating point.

Question 9

Why is my pump motor tripping or drawing high amps?

Accepted Answer

Primary causes: fluid specific gravity higher than design assumption, mechanical binding in rotating parts, voltage drop on Indian grid. Solutions: recalculate BHP for actual SG and throttle discharge valve, inspect wear rings for seizure, verify terminal voltage is within 415V ±6%.

Question 10

Why is my pump discharge pressure low?

Accepted Answer

Primary causes: motor speed too low, impeller diameter too small, excessive internal clearances. Solutions: verify VFD output frequency or check motor poles match supply frequency, replace with full-diameter impeller, adjust or replace impeller wear rings.

Question 11

Why is the pump running but delivering no liquid?

Accepted Answer

Primary causes: suction isolation valve closed, vapour lock in casing. Solutions: open suction isolation valve fully, vent pump casing to atmospheric pressure to release trapped vapour.

Question 12

What causes air in the pump suction line?

Accepted Answer

Primary causes: leaking packing gland drawing in air, low liquid level in supply tank. Solutions: tighten gland follower or upgrade to mechanical seal, install float-operated level controls on supply tank.

Question 13

What causes impeller wear or erosion?

Accepted Answer

Primary causes: pumping abrasive slurries without correct metallurgy, cavitation pitting damage. Solutions: upgrade to hardened alloy impeller or rubber-lined casing, eliminate cavitation root cause.

Question 14

What causes pump bearing failure?

Accepted Answer

Primary causes: lubrication contamination from water or dirt ingress, misalignment strain on bearings. Solutions: replace bearing isolator seals and change to clean oil or grease, perform laser or dial indicator alignment.

Question 15

What causes pump coupling failure?

Accepted Answer

Primary causes: severe misalignment, incorrect shaft end gap spacing. Solutions: correct both parallel and angular alignment with dial indicators, adjust coupling hub spacing to manufacturer specification.

Pump Troubleshooting Guide