GB828161A - Improvements relating to variable delivery pumps - Google Patents

Abstract

828,161. Reciprocating pumps. DOWTY EQUIPMENT Ltd. Aug. 6, 1957 [Aug. 7, 1956], No. 24198/56. Class 102(1). [Also in Group XXIX] In a pump of the type described in Specification 678,470 the flow control valve 25 comprises a piston 26 subjected to the output pressure of the pump 18 through a passage 28, the head of which engages a piston 63 slidable in a chamber 62 in a valve spool 60. A restricted passage 64 interconnects the end faces of the piston. A push rod 65 engages the end of the piston 63 and engages a member 66 loaded by a spring 29. A light spring 69 engages the member 66 and the spool 60. The spool is provided with a recess 72 having a tapered edge which controls flow from a port 49, connected to the outlet of the pump 15, into the recess and so to the open port 50 connected to the inlet of pump 18. A slow rise in output pressure of the pump 18 above a predetermined pressure slowly raises the piston 26 so that oil flows from one side of piston 63 to the other until the piston 63 engages and lifts the spool 60 whereby communication between the port 49 and the recess 72 is closed. Sudden rises of output pressure does not permit flow through the passage 64 and the spool valve is immediately actuated. Further rise in pressure lifts the piston 26 sufficiently to connect passage 28 to passages 76 and exhaust. The end of the piston 26 is provided with a dash-pot piston 57.