Patent GB-902850-A (GB)
Title: Improvements in hydraulic speed governing system with reset relay
IPC: G05D13/00
Filed: 1959-03-20
Abstract: 902,850. Fluid-pressure servomotor-control systems. GENERAL ELECTRIC CO. March 20, 1959 [April 10, 1958], No. 9749/59. Class 135. In an hydraulic speed governor for a steam turbine driving, e.g. a paper-making machine, comprising speed-sensitive governor weights 12 driven through gearing by the turbine 1 and a leak-off pilot valve 8a controlling ports 8f in a follow-up sleeve 8d to control movements of a piston 5a slidable in a cylinder 9 and through a lever 2 regulate the turbine throttle valve 1a, a spring-loaded reset piston 13 slidable in the cylinder 9 is spaced from the piston 5a to form a pressure chamber 9a therebetween. The piston 13 is connected by a lever 15 to the follow-up sleeve 8d and by a lever 11a to a reset slide valve 11 to adjust the quantity and pressure of liquid in the chamber 9a to maintain accurately a preselected speed with no deviation from the desired speed as a function of change in load. Pressure liquid is supplied to a casing 6 housing the pistons and valves by a turbine driven pump 16b through a line 16 having a restriction 16a and is returned from the casing to the pump inlet by a passage 10b. To initially open thethrottle valve 1a operating liquid is supplied to the casing 6 from an auxiliary source, e.g. an electrically-driven pump. The pressure of this liquid raises the piston 5a and through the lever 2 the throttle valve 1a against its spring 1c to establish an operating pressure P1 below the piston. 5a. At this stage the reset piston 13, slide valve 11 and sleeve 8d are in their lowermost positions so that pressure liquid is admitted to the chamber 9a past cut-off edges 11e, 11f until the piston 13 is raised against its spring a sufficient amount to raise the valve 11 to cut-off flow between the edges 11e, 11f and establish an operating pressure P2 in the chamber 9a. At the same time the sleeve 8d is raised to a position predetermined by the adjustment of the fulcrum 15b of the lever 15 to pre-select the turbine speed. On the opening of the turbine stop valve 1e, the turbine will rotate together with the pump 16b which when the operating pressures P1 and P2 are reached, takes over from the auxiliary pump which is then shut down. When the preselected speed is reached the weights 12 lower the valve 8a until the ports 8f are just closed. Should the turbine speed depart from the pre-selected speed, e.g. increase, the valve 8a will fall to open the ports 8f to lower the pressure beneath the piston 5a whence the piston moves downwardly to move the throttle valve towards closure. The piston 13 immediately follows the movement of the piston 5a intially at the same speed to lower the sleeve 8d to follow up the movement of the valve 8a and also lower the slide valve 11 so that liquid is admitted to the pressure chamber 9a which slows up the downward movement of the piston 13. When the throttle valve la has been closed sufficiently to restore the speed to its preset value, the ports 8f will again be closed and the downward movement of the piston 5a arrested to reestablish the pressure P1. Liquid however continues to enter the chamber 9a until the pressure P2 is re-established and the piston 13 moved upwardly to cut off flow between the edges lie, 11f. Conversely with a decrease in the pre-set speed of the turbine the pistons 5a, 13 will rise with liquid being drained from the chamber 9a until steady conditions are reestablished. The spring 14 then acting on the piston 13 to move it downwardly to re-establish the P2 pressure.