Possible causes	Recommended action
Pump operating in reverse rotation.	Change the rotating direction to the appropriate way.
Gate valve is damaged.	Repair or replace the gate valve.
Large voltage drop	Contact the electric power company and take measures.
Pump for 60Hz is operated in the 50Hz zone.	Check nameplate and replace the motor.
Discharge head is high.	Review the plan
Significant loss in piping.	Review the plan
Air intrusion because of the low driving water level.	Raise water level.
Leaking from delivery pipe.	Inspect and repair
Discharge pipe is clogged.	Remove foreign objects from the discharge pipe.
Foreign object is stucked to suction opening.	Remove foreign objects.
Pump is clogged.	Disassemble and remove foreign objects.
Impeller is worn out	Replacing impeller