GB1282101A - Improvements in fluid pressure operated mechanisms - Google Patents

Abstract

1282101 Fluid-pressure jacks T P PRIESTLEY 8 Aug 1969 [12 Aug 1968] 38440/68 Heading B8J [Also in Divisions B5 and F1] Fluid pressure operated mechanisms, e.g. presses and jacks, operate in two stages, the first high rate/low thrust and the second low rate/ high thrust obtained by an elongated sliding plunger moving in a blind-ended bore in the piston (or alternatively in the cylinder) of the mechanism to give the initial high rate movement of the piston (or cylinder) and allow thereafter the fluid pressure to be released or build up to the pressure necessary for the high thrust stage. The mechanism is double acting and on its return stroke provides adequate thrust e.g. for stripping. In its simplest form, Fig. 1, the mechanism comprises a plunger 17 moving in a loose sliding fit in a composite bore 15 in the piston 13. The latter comprises a removable bush 41 formed with the smaller portion of the bore 15 and a fluid passage 43, and a main shank containing the enlarged portion 19 of the bore 15, and in its wall a fluid passage 55 with an adjustable restriction 53 therein, controlled manually or by devices e.g. a pressure sensitive transducer or a mechanical device, to give a desired thrust/ displacement characteristic to the piston. The plunger abuts an adjustable bush 31 on the end wall of the cylinder. The bush 31, bush 41 and plunger are all replacable to permit variation in the stroke characteristics of the moving parts. Fluid flow is controlled by changeover valve 21 and a one-way valve 37. To move piston 13 to the right on its working stroke, fluid, e.g. oil, is admitted at port 29, driving the plunger into engagement with bush 31. Thereafter fluid pressure is transferred to the end face 35 of the chamber 19, continuing the movement of the piston until the plunger uncovers the inner end of channel 43, which coincides with contact with the work. Then fluid passes down channel 43 to act on the broad end of the piston giving the low rate/high thrust characteristic desired. The return movement of the piston is initiated by opening pressure responsive valve 37, changing valve 21 to feed to part 47 on the right hand side of the piston and opening part 27 to sump. In Fig. 2 (not shown) there are four plungers in bores in the end wall of the cylinder operated accumulatively. Fig. 3 (not shown) describes the operation of a transducer in conjunction with an amplifier and electromechanical converter to control the valve 53 in its control of the rate/thrust characteristics. There may be a blind ended bore on each side of the piston, each containing a plunger operated similarly to that of Fig. 1 (Fig. 4, not shown). A compact form and operation of this double bored piston is described with reference to Fig. 5 (not shown). In the jack of Fig. 6 (not shown) fluid is pumped from a cylinder (523) by a piston (527) into a cavity (553), Fig. 7 (not shown), at one end of a blind bore containing a plunger (545) to extend the plunger until a platen (575) abuts an upper work surface whereupon it is forced downwards to cause an operating rod (591) to open a valve (571) and allow fluid to pass down a pipe (561) into a space below a piston (519) to develop a full thrust to lift the work surface. The mechanism can have a stationary piston and movable cylinder, or both piston and cylinder can be movable.