Why Balancing Leak Off In Boiler Feed Pump

shiv....

Are you refering to the pipe/tube that starts and terminates at the pump or are you talking about the line that goes from the pump discharge to the deaerator ?

For the former, it is a line to balance the pressure/loadings on a multistage pump. In the case of the latter, it is a minimum flow line to protect a multistaged pump from destruction in the event that the discharge piping is closed.

Like most questions from the third world, we cannot know what you mean unless you are complete and explicit in your problem description.

For thrust load balance of the pump assembly, portion of balancing drum or disc is exposed to the high pressure water. Some calculated clearance is given to maintained the flow through that path and the leak-off is directed to wards the low pressure stages, generally suction side of first stage. The leak off is such that it will not effect pressure on lower pressure side where it is injected. If this leak-off increases, thrust balance will be disturbed and pump needs maintenance at that time.

In addition to the reply referred in this post, Leak-Off connection is very much essential for the boiler feed water pump. If the delivery valve is shut-off, there will not be any water discharge from the pump and the water will be churned continuously and the water temperature will RISE because certain amount of energy is spent while the pump is operating and the churning will result in Rise in temp. of the water inside the pump.

In order to limit the temp. rise with in the pump, some minimum quantity of water should flow out of the pump, when the feed water flow is shut off in to the drum.

DHAYANANDHAN.S