Patent GB-633507-A (GB)
Title: Improvements in fluid-driven pump control
IPC: F04D15/00
Filed: 1947-05-28
Abstract: 633,507. Fluid-actuated valves. SCHELLENS, C. A., and SHERMAN, A. L. May 28, 1947, No. 14189. Convention date, Dec. 2, 1943. [Class 135] [Also in Groups XXVI and XXXIV] A control mechanism for a turbinedriven pump, particularly for supplying feed-water to boilers, comprises a valve unit for controlling the working- fluid supply to the turbine, acted upon in a direction to close the valve by the pressure of the working-fluid leaving the valve, in a direction to open the valve by the pump delivery pressure, and by additional means acting with the delivery pressure; the valve is normally open, but tends to close when the delivery pressure drops to prevent overspeeding, e.g. if the water supply fails, the additional means referred to being arranged so that the pump does not stop completely, but idles. The valve is used for normal control of the turbine, so that it cannot be found out of order in emergency; this control may be automatic, to maintain constant the delivery pressure or some other factor, and is exercised by controlling a small flow of fluid to or from the valve unit, so that the control may act at a distance. A centrifugal trip mechanism is provided to shut the valve completely if overspeeding occurs in spite of the main control. Arrangements are made for compensating the control mechanism for variations in the pump inlet and turbine exhaust pressures, and for the effect of cutting in additional turbine nozzles to maintain output when the turbine inlet pressure is low. Fig. 2 shows a valve unit 42 incorporating a doublebeat valve 50 for control of a steam turbine driving a pump, with an automatic control valve 148 for maintaining the pump delivery pressure constant. The steam in the outlet chamber of the valve 50 presses on a piston 66 tending to close the valve and a pipe 130 connected to the delivery side of the pump applies the pressure thereat to a piston 124 which acts on a lever 78 tending to open the valve 50; a spring 88 acting on the rod 86 of the piston 124 constitutes the additional means referred to, and the centrifugal trip mechanism closes the valve by lowering the fulcrum 80 of the lever 78. The rod 86 and a rod 102 by which the lever 78 exerts pressure on the underside of the piston 66 are connected to the lever 78 by knife-edge bearings (see Group XXXIV); the rod 102 carries the piston of a dashpot 112. At normal steam and water pressures and full delivery volume the valve 50 has a slight bias to the open position, its position being determined by a hand spindle 164 which may also be used to reduce the steam flow when required to reduce the pump delivery. If the pressure in the pipe 130 (i.e. the pump delivery pressure) falls, the steam acting on the piston 66 closes the valve 50 until it is balanced by the force of the spring 88 to keep the turbine idling; the turbine can thus be controlled by manually or otherwise throttling the flow in the pipe 130, and in the embodiment shown this is done by an automatic valve 133 which acts to keep the pressure in the pipe 130 constant. This valve is lifted by the pressure acting on its lower end, against the force of a hand-adjusted spring 150, to throttle the flow of water to the piston 124; a hand-controlled byepass (not shown) is provided to connect the pipe 130 to the underside of the piston 124 when the action of the valve 133 is not required. In order to compensate for the effect of variations in the turbine exhaust and pump suction pressures, the underside of the piston 66 is connected by a pipe 74 to the turbine exhaust and the upper side of the piston 124 by a pipe 128 to the suction side of the pump, both these pistons being so fitted as to allow leakage past them. Leakage along the stem of valve 133 also passes to the pipe 128 by a passage 120. A hand-valve (Fig. 7, not shown) is provided to cut in extra nozzles in the turbine to maintain power when the steam pressure drops, and this results in steam pressure being applied to a chamber 208 in the upper part of the main valve unit to act on the upper end of the spindle of the valve 50, so that the reduced steam pressure acts on a larger area to maintain the balance against the water pressure; the chamber 208 is open to exhaust pressure when the hand-valve is closed. U.S.A. Specification 1,725,722 is referred to.