Patent GB-715111-A (GB)
Title: Improvements in or relating to hydraulic control apparatus
IPC: F15B15/20
Filed: 1949-02-01
Abstract: 715,111. Hydraulic control apparatus. BENDIX AVIATION CORPORATION. Feb. 1, 1949 [Feb. 2, 1948 ; Aug. 17, 1948], Nos. 2747/49 and 2748/49. Class 69 (2) In hydraulic control apparatus, for example for operating implements used with tractors, comprising a motor and a control valve for the motor, having a cylinder and a piston therein, the piston is formed with lands and is operable to control the flow of liquid from a pressure port through the valve to the motor and from the motor through one end of the cylinder to exhaust, and the exhaust passage from the cylinder end is provided with a restriction therein whereby the pressure drop across the restriction builds up a pres-  sure in the cylinder end which assists the movement of the piston away from its neutral position. As shown, the motor comprises a jack unit 15, to which a valve unit 16 containing the valve is detachably secured. The valve is urged towards the neutral position by means of springs, but can be manually actuated by means of a lever 49. When the valve is moved to the left, liquid from a pump flows to the left hand side of the jack piston and liquid from the opposite side of the jack piston is exhausted by way of a passage 28, port 33, orifice 387a and passage 381 and port 389 in the valve to an outlet 53. If the valve is moved only a small amount away from the neutral position and then released, the pressure drop across the orifice 387a is small and the pressure on the end 38a of the valve is insufficient to overcome the restoring force of the springs and the valve returns to neutral. If, however, the valve is fully opened, the pressure drop across the orifice 387a is increased and the pressure on the end 38a is sufficient to retain the valve in the open position. Means are provided to restore the valve to its neutral position when the jack piston reaches a desired position in its stroke, comprising adjustable collars, one only of which, 26, is shown in Fig. 3, on a member 23 attached to the jack piston rod and co-operating with the valve operating lever 49 which is attached by means of a pin 48 to an extension 387 of the valve. The valve lever can be rocked about a fulcrum member 92 (Fig. 3) so that it is out of the path of the collars, in which case the stroke can be increased. By further rocking the valve lever can be made to co-operate with adjustable stops. By holding the lever against a stop the valve is opened to a small extent only and when it is released the spring 42 restores the valve to neutral position. The valve operating lever has a bifurcated end which straddles a stationary screw 82 and is normally retained in position by a spring 83. The lever carries an operating handle 90 which extends through a pair of holes in an intermediate U-shaped portion of the lever 49 and can rotate therein. A torsion spring 90c urges the handle towards the fulcrum member 92. An auxiliary motor can be connected to the circuit by connecting the opposite ends of its cylinder to a normally plugged port (not shown) in the jack cylinder and to a normally plugged port 54 in the valve unit. The port 33 is blocked. Each port is balanced by means of an opposite blind port. For example the port 31 has a balancing blind port 31a. In some positions of the valve the land 382 completely covers the port 31 and this land is provided with a circumferential groove 382a which equalizes pressures in the ports 31 and 31a. Similarly a groove 385a is provided in the land 385. A relief valve is provided and it discharges through a port located above the outlet port 53. In a modification, Fig. 10, the valve is centred by springs 540, 541 and spring retainers 543. 544 function also as valves which open under pressure of the return flow of the liquid. The valve is held in the open position, but is restored on the completion of the jack stroke by the pressure liquid leaking away past an unpacked flange 545 of one of the spring retainers.