Patent GB-839318-A (GB)
Title: Improved hydraulic apparatus
IPC: F15B11/05
Filed: 1959-01-22
Abstract: 839,318. Reciprocating pumps. ALLISCHALMERS MANUFACTURING CO. Jan. 22, 1959 [Jan. 31, 1958], No. 2473/59. Class 102(1). [Also in Group XXIX] A hydraulic system comprises a motor 105 supplied with fluid pressure from two separate and independent fluid pressure circuits, supplied with fluid pressure from separate pumps, 12, 13, relief valve means 28 in the first circuit operable automatically upon attainment of a first predetermined pressure to by-pass the output from the pump 12 whereby the pressure of the fluid is lowered to avoid excess heating thereof, and pressure relief means 88 in the second circuit operable automatically to by-pass the output from the pump 13 upon attainment of a second predetermined pressure, which is higher than the lowered pressure in the first circuit. The pumps 12, 13 are reciprocated by camfollowers 14 engaging a common camshaft, the fluid from the pumps 12 passing through passages 18 to a manually controlled by-pass valve 17 through which fluid flows to one-way valves 23 and a pressure manifold 21 or to a return pipe 68. From the manifold, the fluid passes through a one-way valve 55 to a pipe 24 leading to the motor 105 which may be arranged on an agricultural tractor to lift a load W. The manifold is also connected by a pipe 29 to the relief valve 28 which has a passage 37 normally closed by a ball 38 urged against its seating by a spring pressed piston 39, the piston, in that position, closing a passage 30 communicating with a sump. The pressure required in the manifold to displace the ball from its seating to open the valve is greater than that required to keep the valve open and by-pass the fluid from the manifold through the passage 30 to the sump, the lowered pressure in the circuit preventing excess heating of the fluid.. The pressure required to open the valve may be varied by spacing washers placed at the back of the spring 41 engaging the piston 39. The pump 13, which is smaller than the pump 12, is also connected by the valve 17 and a one-way valve 27 to the pipe 24 leading to the motor. A branch pipe 109 from the pump is connected by the adjustable relief valve 88 to the sump and the pressure at which the valve opens to by-pass the fluid to the sump is less than the pressure required to open the valve 28 but higher than the pressure required to keep it open. In operation, the pumps 12 provide the major proportion of fluid to the motor until the piston of the motor reaches the end of its stroke. the build-up of pressure then opening the valve 28 to reduce the pressure and prevent excess heating of the fluid. The pump 13 operates at a pressure controlled by the valve 88 sufficient to retain the piston at the end of its stroke and make-up any leakage of fluid in the motor. A manually controlled valve 97, which is connected to the spool 79 of the valve 17 is operable to connect the return from the motor to a pipe 68 leading to the sump for the return stroke of the motor. The spool 79 has a tapered end portion 81 engaging a spring-urged piston 82 which, when the spool is in the extreme right-hand position opens a port 86 to connect the space to the left of the piston to a discharge pipe 19 from the valve. The movements of the spool to the left are thus damped by the fluid which is trapped to the left of the piston being forced through an orifice 87.