Water-Lifting Devices – Pumps - Practices of Irrigation and On-farm Water Management - page 458

Problem Possible causes Remedial measures

Pump delivers less than
rated capacity

- Air leak in suction line
or pump seal

Close the air leak

- Insufficient available NPSH Increase available NPSH

- Suction line strainer partially
clogged or of insufficient area

Wash out the strainer

- System total head higher than
calculated
- Partially clogged impeller Clean the impeller

- Impeller rotates in wrong
direction

Stop the pump, check the
rotation of the impeller,
install in correct direction

- Suction or discharge valves
partially closed

Check the valves and clean if
necessary

- Impeller speed too low

Loss of prime while
pump is operating

- Water level falls below the
suction line intake
- Air leak develops in pump or seal
- Air leak develops in suction line
- Water vaporizes in suction line

Pump is noisy - Cavitation Increase the NPSHa

- Misalignment
- Foreign material inside pump Align the pump correctly

-Bentshaft
- Impeller touching casing

Pump takes too much
power

- Impeller speed too high Decrease the speed

- Shaft packing too light
- Misalignment Correct the alignment

- Impeller touching casing
- System total head too low
causing the pump to deliver too
much liquid
- Impeller rotates
- Impeller installed in wrong
direction

12.6 Other Types of Pumps

12.6.1 Air-Lift Pump

Air-lift pumps are used where the water level is beyond the suction limit. Air-lift
pumps operate on the principle that a mixture of air and water will rise in a pipe
surrounded by water. An air-lift pump basically consists of a vertical pipe partially
submerged in water and an air supply tube allowing compressed air to be fed into the
pipe at a considerable distance below the static water surface. The mixture of water