GB634109A - Improvements in or relating to grabs - Google Patents

Abstract

634,109. Fluid-pressure servomotor-control systems. ELECTRO-HYDRAULICS, Ltd., SHARP, C. W., and CALDWELL, H. B. Feb. 26, 1947, No. 5627. [Class 135] [Also in Group XXX] A fluid-pressure-operated grab for lifting articles such as bales or barrels comprises a pressure supply system and control means therefor, including a valve operable in dependence upon the difference between the pressure at the grab jaws and a pressure determined by the amount of movement of a member which actuates the system to transmit fluid-pressure to the grab jaws until the said difference reaches a predetermined amount. The grab jaws 8 are mounted on pistons 6, 7 operating in a cylinder 5, fluid for actuating the pistons being supplied from a storage tank 1 by a pump 2 under the control of a valve unit 3 and a piston- and-cylinder device 4. To operate the jaws, a handle 14 is moved in the direction of the arrow 20 to open a valve 12 in the unit 3 whereby fluid flows along the pipe 15, through a port 11 connecting chambers 9, 10 of the unit, and along a pipe 16 to the device 4. At the same time the piston in the device 4 is moved against the action of its spring 22 by the handle 14 so as to open a valve 17 and allow fluid to pass from the pipe 16 through an exhaust port 18 to a pipe 19 leading to the cylinder 5. When the pressure of the fluid entering the device 4 balances the spring 22, the valve 17 is closed by a spring 23 and fluid is maintained in the cylinder at a pressure proportional to the spring load on the handle 14. To release the pressure, a valve 13 in the unit 3 is opened by operating a trigger 24 on the handle 14 to allow fluid to flow back to the tank 1.