Troubleshooting

troubleshooting

The Troubleshooting Guide below allows you to review and diagnose potential problems that may be encountered with SAM Engineering’s range of centrifugal pumps. The guide outlines common pumping problems and failures with probable causes and procedures for checking and correcting possible faults.

Between regular maintenance inspections, be alert for signs of motor or pump trouble. Correct any trouble immediately to AVOID COSTLY REPAIR AND SHUTDOWN.

 

No liquid delivery

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 system head too high Check pipe friction losses. Larger discharge 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. Alternatively, 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. Wrong rotation will cause pump damage.
7. Impeller completely plugged Dismantle pump or use piping hand hole to clean impeller.

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Not enough liquid delivered

CAUSES
CURES
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. For such liquids as gasoline, suction line can be tested by shutting off or plugging inlet and putting line under pressure.  A gauge will indicate a leak with a drop of pressure.
9. Air leaks in stuffing box Increase seal lubricant pressure to above atmosphere.
10. Speed too low See item 5.
11. Discharge system head too high See item 4.
12. Suction lift too high See item 3.
13. Impeller partially plugged See item 7.
14. Cavitation; insufficient NPSH (depending on installation) a. Increase positive suction head on pump by lowering pump or increasing suction pipe size or raising fluid level.
b. Sub-cool suction piping at inlet to lower entering liquid temperature.
c. Pressurise suction vessel.
15. Defective impeller Inspect impeller.  Replace if damaged or vane sections badly eroded.
16. Defective packing Replace packing and sleeves if badly worn.
17. Foot valve too small or partially obstructed Area through ports of valve should be at least as large as area of suction pipe- preferably 1½ times.  If strainer is used, net clear area should be3 to 4 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 Compare rotation of motor with directional arrow on pump casing. Wrong rotation will cause pump damage.
20. Impeller diameter too small (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.

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Not enough pressure

CAUSES
CURES
21. Speed too low See item 5.
22. Air leaks in suction piping See item 8.
23. Mechanical defects See item 15, 16, 17.
24. Obstruction in liquid passages Dismantle pump and inspect passages of impeller and casing.  Remove obstruction.
25. Air or gases in liquid (Test in laboratory, reducing pressure on liquid to pressure in suction line.  Watch for bubble formation.) May be possible to over rate pump to point where it will provide adequate pressure despite condition.  Better to provide gas separation chamber on suction line near pump, and periodically exhaust accumulated gas. See item 14.
26. Excessive impeller clearance Adjust impeller clearance.
27. Impeller diameter too small (Probable cause if none of above) See item 20.

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Pump operates for short time, then stops

CAUSES
CURES
28. Incomplete priming Free pump, piping and valves of all air.  If high points in suction line prevent this, they need correcting. See item 5.
29. Suction lift too high See item 3.
30. Air leaks in suction piping See item 8.
31. Air leaks in stuffing box See item 9.
32. Air or gases in liquid See item 25.

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Pump takes too much power

CAUSES
CURES
33. Head lower than rating; thereby pumping too much liquid Machine impeller's OD to size advised by factory.
34. Cavitation See item 14.
35. Mechanical defects See item 15, 16, 17.
36. Suction inlet not immersed enough See item 18.
37. Liquid heavier (in either viscosity or specific gravity) than allowed for Use larger driver. Consult factory for recommended size. Test liquid for viscosity and specific gravity.
38. Wrong direction of rotation See item 6.
39. Stuffing box too tight (Packing) Release gland pressure. Tighten reasonably. If sealing liquid does not flow while pump operates, replace packing.  If packing is wearing too quickly, replace scored shaft sleeves and keep liquid seeping for lubrication.
40. Casing distorted by excessive strains from suction or discharge piping Check alignment.  Examine pump for friction between impeller and casing. Replace damaged parts.  Check for pipe strain.
41. Shaft bent due to damage - through shipment, operation, or overhaul Dismantle pump and inspect shaft.
42. Mechanical failure of critical pump parts Check bearings and impeller for damage.  Any irregularity in these parts will cause a drag on shaft.
43. Misalignment Realign pump and driver.
44. Speed may be too high (brake hp of pump varies as the cube of the speed; therefore, any increase in speed means considerable increase in power demand) Check voltage on motor.
45. Electrical defects

The voltage and frequency of the electrical current may be lower than that for which motor was built or there may be defects in motor.  The motor may not be ventilated properly due to a poor location.

46. Mechanical defects in turbine, engine, or other type of drive exclusive of motor If trouble cannot be located, consult factory.

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24 Duncan Road,
Lilianton, Boksburg, 1459,
Gauteng, South Africa

P.O. Box 17788,
Sunward Park, 1479,
Gauteng, South Africa

+27 (0)11 823 4250

+27 (0)11 823 4943

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