Patent GB-895717-A (GB)
Title: Fluid control valves
IPC: F15B13/08
Filed: 1960-03-07
Abstract: 895,717. Fluid-pressure servomotor-control systems; valves. NEW YORK AIR BRAKE CO. March 7, 1960 [April 22, 1959], No. 7931/60. Class 135. [Also in Group XXI] The power-operated bucket or shovel 16, Fig. 1, of a tractor mounted backhoe 11 is operated by three double-acting fluid-pressure motors 21, 22, 23 which, respectively, control the " lifting," " filling " and " tilting " operations ; the motors are connected to ports 24, 25, 24a, 25a and 24b, 25b of a control valve 26, which comprises three identical sliding valve plungers 32, 33, 34, Fig. 2, the housing for which includes an exhaust manifold 45 with an outlet 31 opening into each end of the plunger bores via annular chambers 36, 44 and two supply manifolds 46, 47, leading from an inlet 29 to annular chambers 38, 42 in each plunger bore whilst an unloading passage 48 extends through the housing between the supply and exhaust manifolds and intersects further annular chambers 39, 41 in each plunger bore. The motor ports 24, 25, Fig. 1, open into the plunger bores through other annular chambers 37, 43, Fig. 2. With the plungers urged by springs 62 to the neutral position shown, the plunger lands 51, 52 isolate the motor chambers 37, 43 and hydraulically lock all the motors; the inlet 29 is in free communication with the outlet 31 via the passage 48 so that the pump, not shown, connected to the inlet 29 is unloaded. Upon shifting the plunger 32 rightwardly to lift the bucket, the rod end of the lifting motor 21 is connected to the inlet 29 through the manifold 46, chamber 38, plunger passages 56 and bore 53, a check valve 59 in the plunger, further plunger passages 55, and chamber 37 whilst an exhaust path is established between the piston end of the motor 21 through chamber 43, plunger passages and bore 57, 58 and 54, chamber 44 and manifold 45. Concomitantly land 51 isolates chambers 39 and 41 to close the passage 48 and load the pump. The bucket is lowered by moving the plunger 32 to the left. The bucket-filling operation is effected by moving plunger 33 to the right whereupon the bucket is moved in the same direction ; movement of the plunger 33 to the left produces a leftward traversal of the bucket. Should the load on the bucket become excessive when the latter is in its rightward operating position the pressure in port 24a and hence a chamber 37a will rise and open a pressure relief valve 69 in the plunger 33, the relieved fluid flowing to exhaust via conduit 65 and restriction 73, the resulting back pressure in the conduit 65 acting upon the left end 64 of plunger 32 shifting the latter rightwardly and causing motor 21 to lift the bucket until the load is no longer excessive, when the motor 22 will recommence movement and so reduce the pressure thereby enabling the relief valve 69 to close and a spring 62 to re-centre the plunger 32 and stop the motor 21. A ditch with a stepped side wall as shown in Fig. 1 may be produced by repeated automatic operation of motor 21 in this manner. The back pressure acting on the end 64, Fig. 2, is only just sufficient to overcome spring 62 so that the operator can override this automatic control by exerting a centering force on plunger 32 slightly greater than that produced by the back pressure. The pressure in the rod end of motor 22 is prevented by land 51a from acting on the relief valve 69 whereby external loads acting on the bucket cannot cause movement of the latter so enabling a straight-walled ditch to be cut.