Patent GB-910252-A (GB)
Title: Slide plate type hydraulic valve
Inventor: HARE RICHARD CHARLES
IPC: F15B11/20
Filed: 1960-04-13
Abstract: 910,252. Lift trucks. APPLIED POWER INDUSTRIES Inc. April 13, 1960, No. 13281/60. Class 78 (3). [Also in Groups XXIX and XXXI] A sliding plate type hydraulic valve, Figs. 1, 3 and 5, for controlling, through fluid motors, the operations of excavating or moving equipment, power lift trucks or the like, comprises a housing consisting of a cylinder-tank plate 11, a centre slide retainer plate 12 having an elongated slot 16 defining a valve chamber and a pressure plate 13, the cylinder-tank plate 11 having two cylinder ports C1, C2 and three tank ports T1, T2, T3 all communicating between the exterior of the housing and the valve chamber, and the pressure plate having a pressure supply port P communicating through a "series" inlet port P2 and through a "parallel" pressure inlet port P1 with the chamber at spaced locations (Fig. 3), a slide plate 18 in the chamber for reciprocation between a central neutral position and left or right fluid directing positions, this slide having three elongated slots 30, 31, 32 spaced along its length and when moved to left or right placing the " parallel " pressure inlet P1 in communication with one or other of the two cylinder ports C2, C1 through one of the three slots (31) and placing one of these cylinder ports in communication with a corresponding one of the two tank ports T1, T2 through a corresponding one of the other two slots 30, 32, the slide also having a pair of pressure balancing holes 33, 34 extending therethrough between the slots 30, 31, 32 and being adapted in neutral position to block the " parallel" pressure inlet P1 and the cylinder ports C1, C2, the slide also having a " series operation " elongated port 35 which places the " series " pressure inlet P2 in communication with the third tank port T3 in neutral position and when the slide is moved to left or right isolates the " series " pressure inlet P2 from the third tank port T3, the slide further having a second pair of pressure balancing holes 36, 37 extending therethrough on each side of the elongated port 35 which are placed in selective communication with the " series " pressure inlet P2 through this port in left or right positions. A load-holding check valve 15 is fitted on the upstream side of the " parallel " pressure inlet P1. Overpressure in this inlet is relieved through a relief valve 42 which communicates permanently through slot 30 with tank port T1. Thus, in neutral position both cylinder ports are blocked whilst pressure fluid goes through series inlet P2 to tank port T3; and in left and right positions series inlet P2 is blocked, whilst pressure fluid is supplied through parallel inlet P1 via slot 31 selectively to the cylinder ports C1, C2, the pressure at these ports being selectively returned to their corresponding tank ports T1, T2 via slots 30, 32 respectively. In a modified form, a fourth valve position is provided for, wherein the pressure inlet P1, P2 and the cylinder ports C1, C2 are all communicated in common to tank, this position corresponding, e.g. to a jackoperated loader bucket being simply dragged over the ground. In a system, Fig. 6, for controlling through hydraulic motors I, J and K the load lift, load tilt and steering functions respectively of a power lift truck, three such valves are incorporated in primary circuits at B, C and D, these circuits being supplied by a split delivery pump A. This system operates as follows:- Load tilt.-Valve B in neutral position simply directs pressure fluid out through its tank port T3 through conduit 47 to combine with the normal flow to valve C controlling the lift function. In left or right positions of valve B fluid is admitted to rotate the tilt motor J in either direction, this primary circuit including, at E, a relief valve and four check valves providing for relief for either direction of pressure flow. Steering circuit.-Valve D is hydraulically operated through a pilot circuit by an actuator 49. A relief valve F in line 51 from valve C is set at 80 p.s.i. When the operator closes an open centre steering valve at K by turning movement of the steering wheel, pressure is directed through a conduit 50 to shift valve D and allows pump pressure to flow to steering motor K. A relief valve H is fitted in the delivery. Line 52 from motor cylinder I through check valve G2 to relief valve F maintains volume in the steering circuit, the rod end of cylinder I being kept full of oil so that a source of pressure is always available for the steering or pilot valve at K. The arrangement of valves B, C and D is such that steering will always have priority over the lift function. Lift circuit.-The load-holding check and bypass relief valve 15, 42 above mentioned are required only at one place in the system and are incorporated at W with the valve C. With this valve in neutral, pressure fluid flows directly through the valve to relief valve F. In left position pressure is directed via line 54 to the head end of cylinder I to lift the load. Fluid from the rod end of cylinder I is directed either to tank via line 52 or to the steering circuit, depending on the position of the steering valve at K. In right position, fluid from the pump A is delivered through cylinder line Q to relief valve F, the load being allowed to drop by delivery of fluid from cylinder I through line 54 and thence to tank through the tank port T1 of valve C.