GB678470A - Improvements in hydraulic pumping units - Google Patents

Abstract

678,470. Hydraulic pumps. DOWTY EQUIPMENT Ltd., and BOWERS, E. H. March 22, 1951 [March 31, 1950], No. 8172/50. Class 102 (i) A hydraulic pumping unit comprises a first stage lowpressure pump 15, having a by-pass 25 controlled by a spring-loaded valve 36, in series with a second stage highpressure pump 18, both pumps having a common driving means, a conduit 16 connecting the two pumps and containing a shut-off valve 27 adapted to close in response to a predetermined output pressure from the second stage pump, and a fixed restriction 28 by-passing the shut-off valve to allow a reduced flow of liquid when the shut-off valve is closed. The pump 15 is of the gear type and the pump 18 is a radial cylinder pump having a suction gallery 17 from which liquid flows through ports 22 in the plungers 19 to the cylinders 20 and is then delivered through valves 23 to a delivery gallery 24 communicating with an outlet conduit 13 and with a passage 30 leading to the shut-off valve. When the latter is raised it closes the main branch 16a and a reduced flow is maintained through the passage 16b and the restriction 28. Further movement of the shut-off valve allows the liquid in the passage 30 to escape through ports 31 and a return conduit 14. The by-pass valve 36 is loaded by a spring 38 carried by a plunger 37, biased by a second spring 39, in a chamber 42 subjected to the inlet pressure of the second stage pump. When the conduit 16 is fully open the pressure in the chamber 42 maintains the plunger 37 at its upper limit and the by-pass valve is set for high-pressure. When the conduit 16 is restricted the byepass valve is set for lowpressure. A branch 34 communicates continuously with the return outlet 14 through a restriction 35. The pumps 15, 18 are driven from a common shaft.