1. Lack of prime.
2. Loss of prime.
3. Suction lift too high.
4. Discharge head too high.
5. Speed too low.
6. Wrong direction of rotation.
7. Impeller completely plugged.
Fill pump and suction pipe completely with liquid.
Check for leaks in suction pipe joints and fittings; vent casing to remove accumulated air.
If no obstruction at inlet, check for pipe friction losses. However, static lift may be too
great. Measure with mercury column or vacuum gauge while pump operates. If static lift is
too high, liquid to pump must be raised or pump must be lowered.
Check pipe friction losses. Large piping may correct condition. Check that valves are
Check if motor is directly across the line and receiving full voltage. Or frequency may be to
low; motor may have an open phase.
Check motor rotation with directional arrow on pump casing.
Dismantle pump and clean impeller.
Not Enough Liquid Delivered
8. Air leaks in suction piping.
9. Air leaks in stuffing box.
10. Speed too low.
11. Discharge head too high.
12. Suction lift too high.
13. Impeller partially plugged.
14. Cavitation; insufficient NPSH
15. Defective impeller.
16. Defective packing.
If liquid pumped is water or nonexplosive, and explosive gas or dust is not present, test
flanges for leakage with flame or match. For such liquids as gasoline; the suction line can
be tested by shutting off or plugging the inlet and putting the line under pressure. A gauge
will indicate a leak if pressure drops.
Increase seal lubricant pressure to above atmosphere.
See item 5.
See item 4.
See item 3.
See item 7.
a. Increase positive suction head on pump by lowering pump.
b. Subcool suction piping at inlet to lower entering liquid temperature.
c. Pressurized suction vessel.
Inspect impeller, bearings, and shaft. Replace if damaged or vane sections badly eroded.
Replace packing and sleeves if badly worn.
No Liquid Delivered
17. Foot valve too small or partially
Area through ports of valve should be at least as large as area of suction pipe-preferably 1
1/2 times. If strainer is used, net clear area should be three to four times area of suction pipe
18. Suction inlet not immersed deep enough.
If inlet cannot be lowered or if eddies through which air is sucked persist when it is
lowered, chain a board to suction pipe. It will be drawn into eddies, smothering the vortex.
19. Wrong direction of rotation.
Symptoms are an overloaded drive and about 1/3 rated capacity from pump. Compare
rotation of motor with directional arrow on pump casing.
20. Too small impeller diameter (probable
Check with factory to see if larger impeller can be used; otherwise, cut pipe losses or
cause if none of the above).
increase speed-or both, as needed. Be careful not to overload drive