Bell & Gossett P5002169C Series VSCS - Manual (Page 23)

21
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.
CAUSES CURES
No Liquid Delivered
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 that valves are wide open.
5. Speed too low Check whether the properly wired. Frequency may be too low;
motor may have an open phase. Verify that the driver and speed
matches the pump nameplate speed.
6. Plugged suction diffuser or
strainer screen
Dismantle and clean.
7. Impeller completely plugged Dismantle pump and clean impeller.
Not Enough Liquid Delivered
8. Air leaks in suction piping Test flanges for leakage 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
Check pipe friction losses. Large piping may correct condition.
Check that valves are fully open.
11. Suction lift too high See item 3.
12. Impeller partially plugged See item 7.
13. Cavitation; insufficient NPSH A
(depending on installation) a. Increase positive suction head on pump.
b. Reduce the temperature of the liquid in the suction pipe.
14. Defective impeller
Inspect impeller, bearings and shaft. Determine the cause and
correct.
15. Wrong direction of rotation Compare the rotation of the motor with the directional arrow on the
pump casing. Correct as required.
16. Wrong direction of impeller Reverse the impeller direction on the shaft.
17. Too small impeller diameter
(probable cause if none of the
above) Check with the factory to see if a larger impeller can be used;
otherwise, cut the pipe losses or increase the speed, or both as
needed. Be careful not to overload the driver.
18. Speed too low See item 5.
19. Air leaks in suction piping See item 8.