Bell & Gossett P81875G Series HSC-S Centrifugal Pump - Manual (Page 14)

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C. TROUBLE SHOOTING
Between regular maintenance inspections, be alert for signs of
motor or pump trouble. Common symptoms are listed below. Correct any trouble immediately and AVOID COSTLY REPAIR
AND SHUTDOWN.
No Liquid Delivered
CAUSES CURES
1. Lack of prime. Fill pump and suction pipe completely with liquid.
2. Loss of prime. Check for leaks in suction pipe joints and fittings; vent casing to remove
accumulated air.
3. Suction lift too high. 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 be pumped must
be raised or pump lowered.
4. Discharge head too high. Check pipe friction losses. Large piping may correct condition. Check
that valves are wide open.
5. Speed too low. Check whether motor is directly across-the-line and receiving full volt-
age. Or frequency may be too low; motor may have an open phase.
6. Wrong direction of rotation. Check motor rotation with directional arrow on pump casing.
7. Impeller completely plugged. Dismantle pump and clean impeller.
Not Enough Liquid Delivered
8. Air leaks in suction piping. If liquid pumped is water or other non-explosive, and explosive gas or
dust is not present, test flanges for leakage with flame or match, or by
plugging inlet and putting line under pressure. A gauge will indicate a
leak with a drop of pressure.
9. Speed too low. See item 5.
10. Discharge head too high. See item 4.
11. Suction lift too high. See item 3.
12. Impeller partially plugged. See item 7.
13. Cavitation; insufficient NPSH a. Increase positive suction head on pump by lowering pump.
(depending on installation)
b. Sub-cool suction piping at inlet to lower entering liquid temperature.
c. Pressurization suction vessel.
14. Defective impeller. Inspect impeller, bearings and shaft. Replace if damaged or vane sec-
tions badly eroded.
15. Foot valve too small or partially Area through ports of valve should be at least as large as area of suction
obstructed. pipe – preferably 1 1 / 2 times. If strainer is used, net clear area should be
3 to 4 times area of suction pipe.
16. Suction inlet not immersed If inlet cannot be lowered, or if eddies through which air is sucked per-
deep enough. sist when it is lowered, chain a board to suction pipe. It will be drawn
into eddies, smothering the vortex.
17. 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.
18. Too small impeller diameter. Check with factory to see if a larger impeller can be used; otherwise, cut
(Probable cause if none of above.) pipe losses or increase speed – or both, as needed. But be careful not
to seriously overload drive.
19. Speed too low. See item 5.
20. Air leaks in suction piping. See item 8.