GB820417A - Improvements in reciprocating pumps - Google Patents

Abstract

820,417. Swash plate pumps. INTEGRAL Ltd. Jan 28, 1957 [Nov. 6, 1956; Nov. 15, 1956], Nos. 33879/56 and 34954/56. Class 102(1). [Also in Group XXIX] A hydraulic pump comprises a plurality of hollow pump plungers movable in associated cylinders and means subject to pump delivery pressure for controlling the spill of liquid from the cylinders during the discharge strokes of the plungers, thereby varying the delivery of the pump according to the flow requirements of the system. The pump comprises a casing 100 accommodating a plurality of cylinders and associated plungers 10 reciprocated by a swash plate 13 fixed to a driving shaft 113. Each plunger has a central bore 11 and a lateral spill port 12 controlled by a sleeve valve 24 surrounding the plunger. The spill valves are connected by a plate 15 loaded by a spring 16 and attached by a rod 17 to a differential servo piston 18. The left hand face of the piston 18 is subject through a duct 118 to pump delivery pressure. The right hand face of the piston 18 is subject to pressure which is a function of the delivery pressure fed through a restrictor 20 and duct 19. A spring balanced control valve 21 sensitive to the pressure in the duct 19 maintains the pressure at a predetermined value. Under normal equilibrium conditions the valve 21 is in a floating position. When however, for example, the flow requirements of the system are reduced the pump delivery pressure tends to increase. This increase in pressure felt simultaneously on both sides of the piston 18 causes the valve 21 to open a little further. The resulting increase in flow through the valve 21 causes a drop in pressure on the right hand side of the piston 18, which moves to the right, causing the sleeve valves 24 to increase the amount of spill and reduce the delivery of the pump. A flow limiter 31 may be included in the system to limit the maximum delivery of the pump. A piston 28 balanced by a spring 30 is subjected on opposite faces to the pressure drop across a restrictor 27. The right hand end of the beam 22 engages an elongated slot in the piston 28 such that when the pressure drop across the restrictor reaches a pre-determined value according to the maximum flow requirement the piston 28 moves upwards to open the valve 21 to reduce the pump delivery. The fixed restrictor 27 may be replaced by a variable needle valve operated by a servo piston subject to a pressure differential determined by the speed of a hydraulic motor driven by the pump to maintain the speed of the hydraulic motor constant. The differential servo piston 18 may be replaced by a servo piston having faces of equal area. Instead of the spring 16 the piston rod may be formed with two faces of different area enclosed in a pressurized chamber such that the fluid pressure acting on the larger face tends to move the piston 18 to the left.