|Fig. 1: Steam Boiler Feedwater Pump|
The steam boiler feedwater pump should have discharge pressure which is greater than the operating pressure on the steam boiler. The pressure of boiler feedwater pump is designed to recover all of pressure loss because of friction in feedwater piping and valve, economizer and its connection tube, feedwater control valve, feedwater heater, safety valve, and static head pressure. The volume capacity of the pump when installed in power plant must be same amount of total evaporated water in steam boiler coupled with application of continuous blowdown and spray water into desuperheater.
The outside source of pressure must be provided either form static head if the suction souce is above the boiler feedwater pump or atmospheric pressure if below the pump. Pressure pushes the feedwater up into the pump suction. The pump creates a vacuum by movement of the tight fitting piston or action of the impeller into which the water rushes. Design of steam boiler feed pump must consider pressure and temperature feedwater, so it can recover all of requirement of steam boiler.