GB1020402A - Improvements in two-jaw grabs - Google Patents

Abstract

1,020,402. Grabs for handling materials. POCLAIN. May 14, 1964 [June 11, 1963], No. 20231/64. Headings B8H and B8J. In a grab comprising two jaws articulated symmetrically about the bottom of a frame, the jaws are moved in synchronism by two doubleacting jacks 12, 13 articulated to the upper end of the frame and to each of the jaws. The jacks are operated in synchronism by balancing the flow of hydraulic fluid to each. In the embodiment of Fig. 2 the jacks are placed in series in the fluid circuit, the chamber 13a of jack 13 on the piston rod side of the piston 11a being in fluid communication with the chamber 12b of jack 12 on the side of piston 10a remote from the piston rod 10. The piston area of the chamber 12b is equal to the effective piston area of the chamber 13a, hence with displacement of the piston 11a, the piston 10a is displaced an equal amount in the same direction causing a synchronized movement of the grab jaws in either direction. The spring- loaded valves 19, 31 and 17, 30 are incorporated in each piston 11a, 10a to cause a balance of fluid pressure in each jack at the end of each stroke, the appropriate valve stems 19a, 31a, 17a, 30a engaging the end walls of the jack cylinders to open the downstream valves and the increased fluid pressure on the upstream valves opening the same. In the embodiment of Fig. 3 the two jacks are placed in parallel in the fluid circuit, the supply flow being balanced by a flow divider 23. The latter is supplied from a fluid pipe 26 and the fluid passes into a chamber containing a freely moving piston 29 via ducts 27, 28 and equal constricted orifices 27a, 28a. Any excessive resistance to the travel of one of the jacks causes the piston 29 to move and restrict the supply of fluid to the other jack, whereupon a synchronism of jack movement is effected. Non-return valves 32, 33 are provided in the flow divider to permit discharge of fluid from the jacks when they move in the opposite direction. In the latter case fluid is supplied to the jacks by pipes 24, 25 which also may be coupled to a further flow divider.