Patent GB-671904-A (GB)
Title: Improvements in or relating to a tractor propelled material-handling apparatus
IPC: E02F3/42
Filed: 1950-09-05
Abstract: 671,904. Scoop arm load-handling machines. RUSTON-BUCYRUS, Ltd. Sept. 5, 1950. [Sept. 17, 1949] No. 21841/50. Class 78 (iii). [Also in Group XXIX] In a scoop arm load handling machine of the kind in which a hydraulic piston-cylinder assembly pivots the bucket to dump the load, a normally closed short circuit valve is connected between the pressure chambers on each side of the piston, said valve being opened when a predetermined pressure is exerted on the piston to effect dumping, whereupon the speed of the dumping movement is increased. A pair of arms 16 are luffed by a pair of piston-cylinder assemblies 20 and the bucket 21, pivoted at the ends of these arms, is tipped about a pivot 22 by a pair of piston-cylinder assemblies 30 which are connected with the bucket by cross heads 27 and transmission rods 25. The hydraulic circuit, Fig. 13, includes a pump and reservoir unit 31, the pressure output from which is controlled by a piston 34 ; a distributor valve 41, which connects the unit 31 with either the cylinders 20 or 30 ; the short circuit valve 61 and a single control lever, Figs. 11, 12 (not shown) which by pivoting in two perpendicular planes controls both the piston 34 and the valve 41. When it is desired to dump the bucket slowly a low pressure is applied to the ends 30L of cylinders 30 and the fluid flows as indicated by the arrows in Fig. 13, the fluid displaced from the ends 3OR of the cylinders passing through ports 62, 63 of the valve 61 and thence back to the reservoir via a duct 73, a hollow bored shuttle valve 78 (see Fig. 3), holes (not shown) arranged radially around the top 79 of the valve and bore 64, all in the short circuit valve 61, and distributer 41. When it is desired to effect fast dumping, for example to shake off material adhering to the bucket, the pressure of the fluid supplied to the ends 30L is increased whereupon the pressure of the displaced fluid from ends 3OR is sufficient to lift shuttle valve 78 against seating 78a so cutting off the return flow through port 64 and admitting fluid beneath valve 81 which then lifts and puts ports 62, 63 in communication with ports 65, 66 ; thus the fluid displaced by the pistons is returned to the ends 30L of the cylinders, together with fluid from the unit 31, and causes the pistons to move further than they would if supplied with fluid from the unit 31 alone. The shuttle 78 has a bleeder valve 79a which limits the pressure in the system during fast dumping. If the shuttle valve 78 sticks in its raised position and pressure is generated in ends 30L of the cylinders by contact of the bucket with the ground, valve 81 closes and interrupts the short circuit between the ends of the cylinder. In a modification (not shown), the bleeder valve 79a is dispensed with and a normally closed one-way valve is placed in parallel with the short circuit valve, said one-way valve opening on a predetermined pressure building up in ends 3OR of the cylinders and remaining open responsive to a pressure lower than the predetermined pressure, due to the valve having a conical headed piston which, when raised from its seating, increases its effective piston area.