Patent GB-724424-A (GB)
Title: Control mechanism for steam generator
IPC: F22B35/00
Filed: 1953-02-23
Abstract: 724,424. Regulating feed-water. VAPOR HEATING CORPORATION. Feb. 23, 1953 [March 1, 1952], No. 5028/53. Class 123 (2). [Also in Group XXIX] In a steam generator, the delivery of fluid fuel to the fire chamber is controlled in accordance with the rate of flow of the feed water, and the supply of feed water is controlled in accordance with the steam pressure by means of a bleed valve in the feed water supply line ; and this second control unit includes means to delay further movement of the bleed valve when a pre-determined steam pressure is attained but such delay means is rendered ineffective upon development of a pre-determined higher. steam pressure. The steam generator comprises concentric groups of coiled tubing and is fired from a spray burner 19, Fig. 1, supplied with air for "atomising" purposes from a line 45 ; and combustion air is supplied by a blower 46 provided with a regulating damper 47. Feed water drawn from a reservoir 20 is forced by a pump 21 along a conduit 23, past a flow detecting unit 24, and through a conduit 25 to the generator coils. Steam is drawn off at 27, passed into a separator 28 from which water is returned to reservoir 20 and then led away for use through a line 30. In its passage through the unit 24, the feed water passes through an aperture in a diaphragm 55, Fig. 4, the area of the aperture being variable by axial adjustment of the position of a tapered pin 62. Any variation in the pressure difference across the diaphragm occasioned by a change in the flow rate is transmitted through a leverarm 65 to a shaft 66 which is loaded by an adjustable spring 68a and which carries a rotary valve 76 at its other end, this valve controlling the supply of pressure oil to, and its exhaust from, a pair of interconnected piston- and-cylinder motors 92, 93. The latter are connected to a rotary cylindrical valve 74 which forms a follow-up seat for the valve 76. Valve 74 carries two cam plates (not shown) which are engaged by followers connected, respectively, to the damper 47 and to a throttle valve regulating the supply of fuel to the burner, and a further cam carried by the valve can actuate a switch controlling a cut-off valve 99 in the burner head 19. A bleed valve 117, Figs. 1 and 2, which serves to by-pass feed water from conduit 23 back to reservoir 20 is actuated by a diaphragm subject to steam pressure in the outlet line 30. The valve is spring-loaded to the closed position and its stem has a lost-motion tapper connection with a stem extending down from a head contacting the diaphragm. This head is loaded by a pair of springs, the tension in which can be varied by means of a lever 150 acting through a rack-and-pinion 132 on to a movable abutment for the springs, and the datum pressure at which the diaphragm starts to open valve 117 is indicated on a scale 154. A pivoted beam 160 connected to the diaphragm head at 162 carries a roller 164 at its free end, and the roller rides on a cam surface 173 which is pressed by an adjustable spring 170 into contact with the roller. As the load on the generator decreases, the steam pressure rises and the roller 164 rides on the upper flat part of cam 173. When the steam pressure attains the value for which the handle 150 has been set, the roller 164 will engage a lip 172 on the cam and further descent of the diaphragm is prevented until a higher steam pressure forces the roller past the lip. A valve 112, Fig. 4, in the line leading to piston 92 retards the movement of the pistons in one direction but allows them to move quickly in the opposite direction to reduce or shut-off delivery of fuel.