Patent GB-681625-A (GB)
Title: Improvements in hydraulic pumps
IPC: F04B49/24
Filed: 1950-05-03
Abstract: 681,625. Reciprocating pumps for liquids. HOBSON, Ltd., H. M., and MOTT, L. F. April 11, 1951 [May 3, 1950], No. 10914/50. Class 102 (i). In a two-stage hydraulic pump in which final delivery pressure is regulated by an offloading valve which reduces the supply of liquid to the second stage pump as the delivery pressure therefrom rises, liquid cannot flow directly from the first stage to the outlet and the off-loading valve is a piston having lands controlling admission and relief ports respectively for the second stage pump, the piston being movable against spring action by increased delivery pressure to reduce progressively the effective area of the admission port and open the relief port correspondingly, the lands and/or ports being so shaped that the delivery decreases progressively, without sudden changes, as the delivery pressure increases. A gear pump 2 delivers liquid, at or above a pressure, determined by a relief valve 22, sufficient to charge the cylinders of a rotary piston pump 10 which discharges at high pressure to a delivery port 20. A passage 19 connects this port with the upper side of a piston 5 actuating, according to the delivery pressure, a piston valve 4, between the lands of which the gear pump effects its delivery. The piston valve 4 controls simultaneously and in opposite sense an admission port 7 for the piston pump and a relief port 8 communicating by a passage 14, variable orifice 17 and a passage 18 with the gear pump inlet 1. A piston 16 exposed at opposite ends to the pressures in the passages 7, 8 respectively, controls the orifice 17 to ensure equalisation of pressures therein and make the flow in the passage 7 a function of the area of the passage which is itself determined by the final delivery pressure. These pressures may however be maintained at other predetermined relative values by inserting restrictions 29 in the passages. Excessive pressure, which might be caused by delivery of liquid already in the pump cylinders when the delivery port 20 is suddenly obstructed, is prevented by the piston 5 in its lowest position, i.e. after closing the admission passage 7, opening a relief passage 21. The piston 16 may be replaced by a diaphragm or be omitted and the port 7 take the form of two ports opened in succession by a piston having two waists. Several admission ports 7 may be provided, each serving a separate group of cylinders of the piston pump, and the ports be cut off by the valve successively. Figs. 6 and 7 show a pump from which the piston 16 is omitted. The gear pump 40, 41 draws oil from a cavity 46 and feeds it through an orifice 48 to the waist or the piston valve 4 which is integral with the actuating piston 5. The final delivery port 20 communicates through a passage (not shown), an annular groove 61 and ports 56 in a sleeve 57 surrounding the piston 5, with the undersurface thereof to lift the pistons 4, 5 against the action of the spring 6 as the delivery pressure rises. After rising pressure has closed the port 7, the piston 5 can rise to put lateral ports 58 into communication with passages 60 leading to the spring chamber 51 to permit the cylinders of the pump 10 to discharge their contents thereinto. Specifications 582,182 and 659,010 are referred to.