Patent GB-587141-A (GB)
Title: Improvements in or relating to the regulation of the feed-water supply in steam generators of the forced-circulation type
IPC: F22D11/00
Filed: 1944-10-20
Abstract: 587,141. Fluid-.pressure servomotorcontrol systems. SULZER FRERES SOC. ANON. Oct. 20, 1944, No. 20323. Convention date, Oct. 22, 1943. [Class 135] The feed-water supply to steam generators of the forced-circulation type is regulated in accordance with both the steam flow and it's temperature. In the. Figure; the feed-water valve 61 is actuated by a servomotor 60 controlled by a pilot valve 59. This valve is actuated by fluid-pressure from a main control valve 39 modified by the action of a compensating or yielding return device generally indicated at 1. The valve 39 is loaded at its upper end by a weighted piston 35 and a spring 36 and is subjected at its lower end to a pressure impulse in a pipe 42 from a thermostatic device 43<1> arranged in the steam pipe 65 preferably near the superheater inlet. A change in the steam temperature from normal due to a change in the demand thus moves valve 39 from its neutral position to supply pressure fluid to a pipe 44, past a valve 45 to a pipe 75, and into a cylinder 2 below a piston 9. The piston 9 actuates, through a rack 11, a cam 14 which loads a spring 27 of a valve 28 which regulates the pressure of fluid to a pipe 33 to act on the control valve 59 of the servomotor 60 to effect an adjustment of the feed-water valve 61. Secured to the piston 9 is a larger hollow displacer piston 4 separating chambers 49 and 58 of cylinder 1 which chambers are in communication respectively with chambers 51 and 48 above and below the weighted piston 35 of control valve 39. Movement of this piston 4 with piston 9 creates a pressure differential across the weighted piston 35 which acts through spring 36 to restore valve 39 to its neutral position and thus slow down the movement of piston 9 and operation of the feed-water valve 61. As the temperature of the steam in pipe 65 and therefore the pressure in pipe 42 is restored to normal, the pressures above and below piston 35 gradually equalize through connecting pipes 56 and a throttle 57 to relieve the pressure of spring 36 and maintain valve 39 in its neutral position. In the event of a sudden and considerable change in steam consumption, a pressure impulse in a pipe 21 proportional to the flow through an orifice 64 in the steam pipe 65 acts on the lower end of another control valve 19 against the pressure of a spring 18 to regulate the fluid-pressure in a pipe 24 to a cylinder 3 above a piston 10. This piston 10 acts through a rack 11 on a cam 15 to load the spring 18 to restore valve 19 to neutral position and also actuates a displacer piston 5 in the cylinder 1 of the compensating device. This results in a change in pressure in the chamber 58 and below the weighted piston 35 to actuate the control valve 39 through spring 36 and so effect an adjustment of the feed-water valve in the manner as previously described, but in accordance with the change in the steam flow. The chamber 49, 51 above the pistons 4 and 35, the chamber 54 below the piston 5, and the non-operative spaces of the cylinders 2 and 3 are interconnected by a pipe 53 which overflows at its upper end 53<1> to atmosphere and manually operable valves 71 and 72 are provided for adjusting the pressure in the inner chambers 58, 48 of the compensating device. In certain circumstances, as when putting the boiler into'service, the temperature of the steam may not produce sufficient pressure in pipe 42 to actuate valve 39 and the displacer pistons approach one another. A distancepiece 78 on piston 5 then opens a valve 76 in the hollow piston 4 which .allows pressure fluid to pass through an axial bore in the piston-rod 6 from a pressure supply pipe 68 to the inner chambers 58, 48 and act upon the piston 4 to effect operation of the feed-water valve. The valve 45 is provided so that in the event of the pressure in pipe 33 falling to close the feedwater valve 61 completely, this valve moves to the left to connect another pressure-fluid supply 46 to the pipe 75 leading to the piston 9 which is raised to open the valve 61 as previously described.