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
CAUSESCURES
1. Lack of primeFill pump and suction pipe completely with liquid.
2. Loss of primeCheck for leaks in suction pipe joints and fittings; vent casing to remove accumulated air.
3. Suction lift too highIf 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 highCheck pipe friction losses. Larger discharge piping may correct condition. Check that valves are wide open.
5. Speed too lowCheck 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 rotationCheck motor rotation with directional arrow on pump casing. Wrong rotation will cause pump damage.
7. Impeller completely pluggedDismantle pump or use piping hand hole to clean impeller.
Not enough liquid delivered
CAUSESCURES
8. Air leaks in suction pipingIf 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 boxIncrease seal lubricant pressure to above atmosphere.
10. Speed too lowSee item 5.
11. Discharge system head too highSee item 4.
12. Suction lift too highSee item 3.
13. Impeller partially pluggedSee 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 impellerInspect impeller.  Replace if damaged or vane sections badly eroded.
16. Defective packingReplace packing and sleeves if badly worn.
17. Foot valve too small or partially obstructedArea 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 enoughIf 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 rotationCompare 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.
Not enough pressure
CAUSESCURES
21. Speed too lowSee item 5.
22. Air leaks in suction pipingSee item 8.
23. Mechanical defectsSee item 15, 16, 17.
24. Obstruction in liquid passagesDismantle 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 clearanceAdjust impeller clearance.
27. Impeller diameter too small (Probable cause if none of above)See item 20.
Pump operates for short time, then stops
CAUSESCURES
28. Incomplete primingFree 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 highSee item 3.
30. Air leaks in suction pipingSee item 8.
31. Air leaks in stuffing boxSee item 9.
32. Air or gases in liquidSee item 25.
Pump takes too much power
CAUSESCURES
33. Head lower than rating; thereby pumping too much liquidMachine impeller's OD to size advised by factory.
34. CavitationSee item 14.
35. Mechanical defectsSee item 15, 16, 17.
36. Suction inlet not immersed enoughSee item 18.
37. Liquid heavier (in either viscosity or specific gravity) than allowed forUse larger driver. Consult factory for recommended size. Test liquid for viscosity and specific gravity.
38. Wrong direction of rotationSee 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 pipingCheck 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 overhaulDismantle pump and inspect shaft.
42. Mechanical failure of critical pump partsCheck bearings and impeller for damage.  Any irregularity in these parts will cause a drag on shaft.
43. MisalignmentRealign 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 defectsThe 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 motorIf trouble cannot be located, consult factory.

For more information on troubleshooting, please contact us on sale[email protected]sameng.co.za or +27 11 823-4250 or fill out the contact form here.

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