GB813644A - Improvements in or relating to steam boiler apparatus and means for regulating the delivery pressure of boiler feed pumps - Google Patents

Abstract

813,644. Feedwater regulators. SCHELLENS, C. A. May 25, 1956 [June 15, 1955], No. 16296/56. Class 123(2) In a feedwater supply system for a steam boiler 10, a feed pump 20 driven by a turbine 21 withdraws water from a tank 16 and delivers it to the boiler drum 12 through a pipe 23 in which is fitted a check valve 24 and a regulating valve 25, the latter being operated manually or automatically to maintain a constant water level in the drum throughout the load range of the boiler. To make the throttling action of the valve 25 more effective by preventing the rise or fall of pressure in the pipe 23 which would occur as the throttle is closed or opened and which tends to offset the throttling action, a constant pressure difference is maintained across the valve by automatic variation of the pump speed, a regulating valve 28 being connected in the steam pipe line to the turbine 21 and being actuated by a device responsive to variations in said pressure difference from the preset value. The device comprises a cylindrical housing 50 containing a piston chamber in which a piston 48 is slidably mounted. The piston rod 44 which projects from the top of the housing, and which is pressed downwardly 'by an adjustable spring 52, is connected by a lever 40 to the stem 34 of the valves 30, 32 of the regulating valve 28. Pipe lines 60, 70 respectively connect the chambers 56, 58 above and below the piston 48 with the steam drum 12 and feed pump discharge line 23 so that when the required pressure difference exists across the valve 25, the piston is balanced, the boiler pressure and spring pressure thereabove equalling the feedwater pressure therebelow. If the pressure difference changes, the consequent piston movement actuates the valve 28 to change the pump speed so that the pressure difference is restored. To prevent overheating of the housing 50 by steam or hot water from line 60 with consequent deposition of scale therein, provision is made for a trickle of feed-water to flow continuously in the line 60 towards the boiler, leakage of water occurring past the piston into chamber 56 and also from a chamber 86 disposed above the chamber 56 and communicating with the inlet pipe 70 through a duct 88. In modifications, provision for the slow leakage into the pipe 60 is made by drilling a small hole in the piston or, where the latter is replaced by a diaphragm, by providing a by-pass pipe having an orifice plate therein.