Patent GB-945367-A (GB)
Title: Improvements relating to valve control in a pumping plant
IPC: H01H35/36
Filed: 1960-03-11
Abstract: 945,367. Fluid-pressure servomotor control systems. SULZER FRERES S.A. March 11, 1960 [ March 11, 1959], No. 8746/60. Heading G3P. [Also in Division F1] A pumping plant comprises a centrifugal pump, delivering through a pipe 6 which contains a movable valve member 8, normally held open during the operation of the pump. When the pump is stopped a wave of negative pressure travels along the pipe and is then reflected from the end of the pipe, undergoing a phase shift of 180.degrees, and returns to the pump as a positive pressure wave, is reflected again as a negative pressure wave, and so on. The valve 8 is arranged to close by an initial rapid closure movement of the valve during the time between the stoppage of the pump and a first pressure minimum in the region of the valve, and thereafter to close only during periods of decreasing pressure in the region of the valve, until the valve is fully closed. The valve closure member 8 is connected to a piston 12 loaded on one side 60 by the pressure in the pipe 6 through a pipe 14 and on the other side 71 by a fluid pressure fed through a pipe 18 and a pipe 16 containing a throttle 15. The flow from the side 71 through a pipe 19 is controlled by a valve 21 connected to a fluid return pipe 23 through a pipe 22, while the fluid supply pipe 18 is connected to the pipe 23 through a valve 24. The valves 21, 24 have electrically actuated pilot valves 27, 28, cooperating with ducts 32, 33 in control pistons 29, 31, which ducts are relatively large compared with bleed ducts 34, 35 in the pistons. When the pump is in operation, the solenoids hold pilot valves 27, 28 upwards and the difference in pressure, due to the size of the ducts, acting on the pistons 29, 31 hold them in the position shown whereby the valves close direct communication between the pipes 19, 22 and 18, 23. When the pump is stopped, the flow of current to the solenoids 25 is discontinued and the pilot valve 27 seats on the piston 29 closing the duct 32.- The pressure on the top side of the piston valve 9 then builds up and moves this valve downwards, together with the pilot valve 27, until it engages the base 73 when the pipe 19 communicates directly with the pipe 22. The piston 12 then moves rapidly to the left until a projection 72 enters an aperture 74 of the pipe 19 and closes this pipe. The valve 8 is then held in a partially open position. The valve 24 acts in a similar way to control the release of pressure from the side 71 of piston 12 through the throttle 15. The solenoid of the pilot valve 28 is controlled by a member 45, which may be a Bourdon tube or a magnetically actuated mercury switch, in response to the pressure in the pipe 6 in the region of the valve such that the current to the solenoid is switched off during a pressure decrease in the region of the valve to allow the valve to close and is switched on to return a control valve 30 to the position shown when the pressure increases in the region of valve 8. In the embodiment shown the valve 8 is held stationary during rise in pressure, but a further control may be provided, acuated by the member 45, to open the valve 8 slightly during rises in pressure which further reduces the pressure surges.