Hydraulic valving system

摘要

1,045,785. Hydraulic apparatus. NEW YORK AIR BRAKE CO. Aug. 6, 1965 [Dec. 3, 1964], No. 33725/65. Heading F1P. [Also in Division G3] In an hydraulic actuation system employing a double-acting piston motor of the differential area type e.g. to move the ejector of an earth moving scraper, means are provided to move the cylinder at high and low speeds respectively at low and high load conditions. Double-acting cylinder 13 is controlled from a 3 position manually operated directional control valve 14, via a shuttle valve 15, whereby for high speed low load operation in the position shown pressure fluid from pump 11 is supplied via passage 18, chamber 25 and passage 18a to the head end of the motor supplemented by flow from the rod end, via passage 19a and valve plunger spool 31, with pressure chamber 33a of spool 29 disconnected from exhaust, via passage 37, to passage 19 by a vent valve 36 which is urged to the closed position by flow from a low pressure relief valve 45, through valve orifice 43. Upon meeting high load conditions a high pressure relief valve 35 operates to supply chamber 33a with pressure fluid to displace spool 29 whereby the exhaust from passage 19a is diverted to passage 19 and the decrease in pressure at the head end arising therefrom closes valve 35 but, since valve 45 stays open, spool 29 is retained locked in position until low load conditions are again attained when valve 45 closes to permit chamber 33a to exhaust to passage 19 and spool 29 to be returned by spring 32 to re-establish flow between the rod and head ends of piston 13 whereupon the pressure in passage 18 rises to reopen valve 45. To retract piston 13, valve 14 is operated to connect passage 19 to the pump 11 and passage 18 to the exhaust 12 whereupon spool 29 is displaced by pressure fluid supplied to chamber 33a, via passage 37, valve 36 and passage 34, so that passages 19, 19a are connected. In an alternative embodiment (Figs. 2-4, not shown), the valves 15, 36 and 35, 45 are incorporated in a single housing with the relief valves 35, 45 and passage 44 communicating directly with the chamber 25 of valve 15 and the conduit 37 communicating directly with valve chamber 27; the valve land 28 is also narrowed to reduce flow resistance through chamber 25.