Patent GB-647237-A (GB)
Title: Improvements relating to pressure-controlling or cushioning appliances
IPC: B21D24/02
Filed: 1948-07-08
Abstract: 647,237. Dashpots. CARTER, A. July 8, 1948, No. 18345. [Class 108(iii)] The invention relates to pressure controlling or cushioning appliances of the kind in which a liquid is acted upon by a main ram or plunger in a primary cylinder and is forced through a resistance opening into a secondary cylinder in order to depress a piston therein against a spring or other elastic medium, and in which a balance pump is operated by a moving part of the appliance so as to return to the secondary cylinder a quantity of liquid to compensate for leakage past the plunger and piston in the primary and secondary cylinders. According to the invention, in the balance pump which comprises plunger and cylinder members, one of which is carried by the secondary cylinder, inlet and outlet passages each controlled by a oneway valve, are provided for respectively admitting fluid into the pump cylinder from a fluid-containing vessel and for discharging fluid from the cylinder into a space above the piston in the secondary cylinder, and a relief passage or space is provided in the wall of the pump cylinder for cooperation with the pump plunger, so that pumping occurs only while the secdary-cylinder piston is moving within an upper portion of its full range of stroke, the relief passage or space being ineffective during this portion of the stroke but cooperating with the plunger to connect the working space of the pump cylinder to exhaust during movement of the secondary cylinder piston during the remainder of its stroke. As shown in Fig. 8, the pressure plate 2 of a press is connected to the rod 3 of a main piston (not shown) which is slidable in a primary cylinder 5 against the action of a spring 37. A secondary cylinder 8 has a corresponding piston 13, the hollow rod 67 of which forms a balancepump cylinder for a pump plunger head 66 carried by a stem 65 rigid with the bottom end wall of the cylinder 5. A passage 69 connects the cylinder 5 with the space of the cylinder 8 above the piston 13 via a valve 42 of the kind which forms the subject matter of Specification 647,236. The pump cylinder 67 is connected with the space of the cylinder 8 below the piston 13 by ports 74 in the pump cylinder walls and upwardly-opening ball-valves 76 in the bottom end wall. Upwardly-opening spring- loaded ball-valves 73 control passages 72 through the pump plungerhead. In operation, pressure on the plate 2 drives the main piston down and so forces liquid into the secondary cylinder 8 to drive down the piston 13 against a return spring 14. Liquid which escapes past the main piston is forced on upward movement of the latter, through a passage 41 leading to the cylinder space 8a below the piston 13. Thus liquid which escapes past both pistons collects in this space which may be replenished through a filling orifice 40. In downward movement of the piston 13 liquid is drawn by the pump plunger from the space 8a into the pump cylinder 67 via the valves 75 and when they are uncovered, the ports 74. On the return movement of the piston 13 this liquid is displaced back through the ports 74 until they are again covered, when the plunger becomes effective to force the liquid through the valves 73 into the cylinder space 8b above the piston. As excess liquid becomes pumped back to the latter space the final upper position of the piston 13 becomes lower and this shortens the effective stroke of the plunger head and brings about a condition of balance. In the construction shown in Fig. 7, the secondary cylinder 8 is rigid with the cover plate of a liquid tank 9 and is connected with the primary cylinder (not shown) by a pipe 7. The pump plunger 55 is secured by a plate 15 and bolts 16 to the cylinder 8. A bore 56 in the plunger 55 opens downwardly into the tank 9 and upwardly into the plunger cylinder 61 via an upwardly-opening ball valve 60. Lateral ports 58 are formed in the wall of the plunger 55. The pump cylinder 61 has a reduced diameter portion 62 which corresponds to the diameter of the plunger 55. In operation, liquid is forced from the plunger cylinder through a spring- loaded ball-valve 64 to the cylinder space 8 above the piston 13, until the ports 58 register with the larger bore portion 63 of the pump cylinder 61. Liquid then passes from the pump cylinder direct to the tank 9 via ports 58 and the bore 56. On the return upward movement of the piston 13, liquid is drawn into the pump cylinder, from the tank 8 through the bore 56 ports 58 (when uncovered) and valve 60. In a third construction in which the arrangement is identical with that described with reference to Fig. 2 of Specification 647,236, the pump plunger 17, Fig. 2 is formed by the lower end of the secondary cylinder piston while the pump cylinder 25 is mounted in a sump on a plate suspended by bolts from the secondary cylinder after the manner of the plate 15 in Fig. 7. The pump cylinder bore is enlarged at 29 and the plunger is formed with axial grooves 23 which terminate short of the plunger head. On the upward stroke of the secondary piston liquid is drawn into the pump cylinder through a ball valve (not shown) in the bottom end wall, and through ports 30 in the pump cylinder wall while these remain in communication with the grooves 23. On the downward stroke liquid is forced from the pump cylinder through a valve 19 into the space above the secondary piston, until the lower ends of the grooves 23 open into the enlarged bore-portion 29. The latter may be replaced by axial grooves in the corresponding portion of the cylinder (Fig. 7a, not shown). A hand pump is provided for pumping liquid manually from the sump direct to the primary cylinder. In a modification, Fig. 6, of the last-described pump construction, the valve through which liquid is drawn into the pump cylinder comprises instead, a downwardly-opening ball valve 51 connecting one of the grooves 23 with the pump cylinder space. The ports 30 open into an annular recess 49 into the pump cylinder wall. The primary cylinder may be connected by pipes to a plurality of secondary cylinders.