GB929481A - Hydraulic mechanism - Google Patents

Abstract

929,481. Hydraulic apparatus. NEW YORK AIR BRAKE CO. Feb. 23, 1962 [April 3, 1961], No. 7107/62. Class 69 (2). An hydraulic control system for the bucket of a loader comprises a double-acting differential-area piston motor 11, a fourposition control valve 12 having an element 19 movable to " hold " and " float " positions, a first conduit 18, 27 and a second conduit 17, 28 connecting the motor to the control valve, a check valve 79 in the first conduit between the control valve and a transverse conduit 29 which joins the first and second conduits and is normally closed by valve means 41 opened by means responsive to the movement of the control element 19 to the " float " position, and means 91 responsive to a pressure in the second conduit greater than that in the first conduit for opening the check valve 79. The valve means 41 is normally urged against a seating 37 closing the passage 29 by a spring 47 when the pressure in the first conduit 27 is equal to that in a space 50 connected by a conduit 109 to a chamber 103 which is closed when the element 19 of the control valve is in any of its positions other than the " float " position, the opposed surfaces of the valve 41 being interconnected by a restricted passage 44. When the element 19 is moved to the " float " position, the conduits 17, 18 and conduits 14, 16 leading to a pump 13 and reservoir 15 are interconnected and, since the pressure in conduit 17 equals that in conduit 18, a spring 84 closes valve 79. The end 19<SP>1</SP> of the control element opens a valve 111 to connect the chamber 103 to exhaust which results in a pressure differential across the restriction 44, moving valve 41 to connect the first conduit to the second conduit so that fluid expelled from a chamber 11a of the motor as a result of the load on the motor can pass through the conduit 29 and a check valve 56 to the second conduit and chamber 11b of the motor, bypassing the control valve 12. Excess fluid from the chamber 11a passes through conduit 17 to the tank. The housing 21 for the check valves may be mounted on the motor and the shortened path for the fluid to pass from one end of the motor to the other under float conditions prevents cavitation occurring in the fluid. When the element 19 is moved to the " raise " position the valve 111 seats and, when the pressure across the valve 41 is equal, the spring 47 seats the valve to close the conduit 29 and fluid from the pump passes through check valve 79 to the chamber 11a of the motor. In the " hold " position of the element, the equal pressures in conduits 17 and 18 permits the spring 84 to close valve 79 so that the pressure in chamber 11a of the motor as a result of the load thereon is not effective on the control valve 12. With the element 19 in the " lower " position, the pressure in conduit 17 is greater than that in conduit 18 and acts on a plunger 91 to open valve 79 and connect chamber 11a to the reservoir. The control valve 12 may be of the type described in Specification 859,658.