Centrifugal Pump Troubleshooting Guide
Centrifugal pumps find their widest application for dealing with large volumes with medium to low heads and viscosities. Centrifugal or radial flow pumps give regular delivery and are quiet in operation. Most of the pumps hence found on board ships are of centrifugal type. They offer trouble free operation if maintained well. Also centrifugal pumps are designed with fewer and simple parts, which means easy maintenance and overhauling.
Failure to deliver water
First, make sure the pump is primed.
- The discharge head is too high, or the suction lift is too high. It should not be more than 4.7m at 29.4 Degree Celsius.
- There may be insufficient speed; the pressure or head at the periphery of the impeller depends upon the tip speed.
- Other faults to look for are an air leak in the suction line, or a broken or plugged up impeller.
- The direction of rotation of the impeller should also be checked.
Pump will not prime
If the pump will not prime, the most probable cause is an air leakage of some sort.
- If there is a leakage at the pump gland, the gland should be adjusted and the recess filled with oil or the stuffing box repacked.
- All joint should be checked for a leak in the pump or suction pipe.
- Make sure that the delivery valve is not open.
- The priming pump float gear, if fitted, should be removed and examined to ensure that the filter protecting the float valve has not become choked, nor the ball disconnected, allowing the spring to close the valve.
- In bilge applications a frequent reason for failure to prime is faulty bilge suction valve.
Failure to build up pressure
If the pump fails to build up adequate pressure, or to discharge water when discharge valve is opened, the following checks should be made:
- Make sure that the pump is primed, that all air has been expelled through the air cocks on the pump casing, and that all the valves in the suction line are open.
- Start the pump again, and if the discharge pressure is still not normal, stop the pump and find the exact cause of failure. It may be that the speed is too low, or that there is air in the water.
- The impeller may be damaged or the wear rings worn, or some other mechanical defect may require attention.
As with complete failure to deliver water, check first the whole pump arrangement:
- The total dynamic head may be higher than that for which the pump is rated, or the suction lift may be too high.
- Check also the temperature of the water and speed of the pump.
- If the above are correct, then the most probable cause is that the impellers have become partially obstructed or choked with dirt from the bilges or pipes.
- Other possible causes are air leaks in the suction or stuffing boxes, defective packing or worn wear rings.
- If there is low output with abnormally high vacuum reading, the probable causes are there is an obstruction in the suction line, such as the blind joint, choked strainer, valve or mud box filter.
Pump loses water after starting
- Check the suction lift and temperature of the water. A leaky suction line may be suspected.
If the alignment of the pump is correct and the foundation secure:
- It is probable that the impeller has become partially clogged so that the balance is disturbed.
- There may also be mechanical faults, such as worn bearings, a bend shaft or an eroded impeller.
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