The boiler feedwater pump loses suction and not delivering water. After air released from the pump, it works normally. Why is the air accumulating in the feedwater pump?
Normally, the main feed pump aboard ship can handle high-temperature water without becoming vapor bound because required net positive suction pressure is designed into the system.
However, vapor may backflow into the pump from the boiler if check valves in the pump delivery line are leaking. This may be experienced on boilers which fittings haven't been overhauled in time. Another possible cause is excessive sludge accumulation in the boiler drum due to water treatment routines that haven't been followed.
