Xylem 9100 Series Base Mounted Centrifugal Fire Pumps AC User Manual download pdf (Page 23)

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 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

voltage. 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

(depending on installation)

a. Increase positive suction head on pump by lowering pump.

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

sections badly eroded.

15. Foot valve too small or partially

obstructed

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

3 to 4 times area of suction pipe.

16. 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.

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.

(Probable cause if none of

above.)

Check with factory to see if a larger impeller can be used; otherwise, cut

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.

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Xylem 9100 Series Base Mounted Centrifugal Fire Pumps AC User Manual Page 23

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