GB911507A - Improvements in or relating to hydraulic ram equipment - Google Patents

Abstract

911,507. Hydraulic apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 20, 1961 [March 18, 1960], No. 9586/60. Class 69 (2). [Also in Group XXVI] A double-acting hydraulic jack comprises a ram 1, Fig. 1, having a piston 13 which is a clearance fit in the bore of the cylinder 2 of the jack and is constrained to follow the general movement of the ram in either direction but is not constrained to remain concentric with respect to the axis of the ram. The ram is formed with a reduced portion 9 which receives the piston 13 and is screw-threaded for a locknut 6, the piston being less in length than the length between shoulders 11, 12 on the ram and lock-nut, respectively. The reduced portion 9 has a clearance of, say, 0.02 inch with the piston which, in turn, has a clearance of, say, 0.004 inch with the cylinder. A pair of rubber or like rings 15 resiliently support the piston on the reduced portion 9. When a pair of jacks are used in a draw-bench such as described in Specification 911,508, draw-bars 3 are secured to each ram by the lock-nuts 6. Fluid pressure from a connection common to both ends of the cylinder acts on both faces of the piston to effect relative movement therebetween, fluid being displaced from the ram side of the piston through the common connection and the pressure being balanced on the two sides of the piston. Relative movement in the opposite direction is effected by connecting the side of the piston remote from the ram to exhaust, the flow of fluid through the clearance between the piston and cylinder causing a pressure drop across the piston to effect the relative movement. In a similar embodiment, two pistons are mounted on the reduced portion of the ram. In another embodiment, the piston 19, Fig. 3, is connected to the ram 18 by a chain 20 and in one direction of movement, the piston abuts a surface 22, and in the opposite direction, the chain constrains the ram to move with the piston. In a further embodiment, the piston is mounted resiliently or with clearance on a stud screwed into the end of the ram. The cylinder of the jack may be formed of sections 2A, 2B having flanges 48 clamped together by bolts 49, seals 51 being provided at the joins. The jack may be constructed as a press and have a cylinder 55, Fig. 11, of concrete reinforced by hoops 56 and bars 57 which are secured to the frame 60 of the press. The piston 53, which is a clearance fit in the cylinder, is mounted with limited axial and radial freedom on the ram 52 by pins 54.