GB903754A - Hydraulic control system - Google Patents

Abstract

903,754. Hydraulic apparatus. APPLIED POWER INDUSTRIES Inc. June 8, 1961 [Aug. 2, 1960], No. 20674/61. Class 69 (2). A control system comprises a master cylinder unit M having head and rod ends connected to head and rod ends, respectively, of a slave cylinder unit S, means 42, 43 for bleeding fluid from the system, and a check valve 20, 21 between a fluid source means P and each end of the slave cylinder unit. The master cylinder unit M has a piston 41 connected by a rod 55 to an operating handle 56 and is connected by conduits 36, 37 to a slave cylinder unit which may actuate a slide valve 10 controlling the supply of fluid from a pump P to conduits 11, 11a, connected to a load (not shown). The pump P, or some other source, is connected by a line 12 to a relief valve 14 and a line 16 which contains a check valve 15 and is joined by a line 18 and the check valves 20, 21 to passages 31, 32 leading to opposite ends of the slave cylinder. The bleed means consists of a groove 42 in the master cylinder connected by a passage 43 to a tank T. In the central position of the piston 41, to which it is urged by a spring 57, fluid supplied by the pump through the check valves 20, 21 continuously passes through the lines 36, 37 to the master cylinder and through the groove 42 and passage 43 to the tank. When the piston 41 is moved to the left to move the slave piston to the right, the fluid supplied to the right-hand end of the master cylinder can continue to flow freely to the tank. Similarly, the fluid can flow freely from the left-hand end of the cylinder when the piston 41 is moved to the right. If the master cylinder unit is arranged at a considerable height above the slave cylinder unit, such as when it is situated at the top of a boom, a valve 60 and relief valve 61 may be inserted in the line to the tank to provide a back pressure and maintain the system full of fluid. In an alternative embodiment, the bleed means from the master cylinder unit consists of passages leading from each end of the cylinder to the tank, each passage having a valve that can be opened to bleed the system.