1. Air entering the suction tube: Make sure the end of the suction tube is deep enough in the water to avoid vortices.
2. Leakage of the suction pipe: Repair the leak of the suction pipe.
3. The sum of the suction and discharge heads is greater than the rated head of the pump: check the total head requirements against the performance curve of the pump.
4. Gas in air or liquid: Check that the priming system is working properly and that the pump is free from cavitation.
