Patent GB-652094-A (GB)
Title: Improvements in or relating to fluid pressure-operated jack systems
Inventor: CALDWELL HARRY BALSHAW
IPC: B64C25/22
Filed: 1947-05-16
Abstract: 652,094. Pneumatic single-stroke apparatus. ELECTRO-HYDRAULICS, Ltd. May 16, 1947, No. 13273. [Class 8(ii)] [Also in Group XXIX] The invention relates to fluid-pressure jack systems and in one form comprises a cylinder 100, Fig. 1, formed with internal flanges 201, 202, and a piston 105 slidable between stops 110 and 111 on a piston rod 106. When fluid is admitted to the left hand end of the cylinder 100, the rod 106 slides with respect to the piston 105 until the latter is contacted by the stop 111, whereupon the piston 105 and rod 106 move together until the piston abuts the stop 202, the jack exerting its greatest effort at this time. In a second form, the piston is arranged within a sleeve and there is additionally provided a floating piston which slides both in the cylinder and between two stops upon a floating rod. With fluid admitted to the left hand end of the cylinder, and the hollow sleeve and floating piston at the limit of their rightward travel, the piston is given a final movement within its sleeve by the floating rod and due to the reduced active area upon which the fluid operates the jack exerts a reduced effort over this last part of the stroke. Fluid may alternatively be supplied through the bore of the piston and piston rod to extend the jack, whereupon the floating piston and rod are not used. If load limiting is not required when using the alternative supply, the floating pistons and rod could be replaced by a single floating piston. In a third form, a cylinder 115, Fig. 3, is divided into two chambers A and B, of differing diameter, by a diaphragm 116 with a central opening. In the chamber A is a floating piston 123 and a sliding piston 122 with a piston rod 121, the latter incorporating a fluid piston 124, whilst in the left hand end of this chamber is a cylinder in which slides an auxiliary piston 125, fixed to the outer attachment lug of the jack. A fluid connection 119 leading into chamber B is permanently coupled to the connection 120 and to extend the jack fluid is supplied to both of these connections causing the sliding piston 122 to move to its extreme rightward position. Fluid entering chamber B through connection 119 acts upon auxiliary piston 125 but due to its small area the latter is not moved away from a stop 128 until the rightward travel of the sliding piston 122 ceases, whereupon further extension of the jack will be accomplished with a reduced effort by the movement of the auxiliary piston 125. Alternatively, fluid at lower pressure can also be admitted into both chambers A and B through a connection 118 in front of the diaphragm 116 in order to extend the jack, which fluid acts simultaneously on both floating pistons 123 and 124, the former moving the sliding piston 122 to the right and the latter operating the auxiliary piston 125 without effecting any reduction in the load exerted by the jack, since the area of piston 124 is larger than that of piston 125.. However, if load limiting is desired, the diameter of chamber B is made smaller than that of chamber A so that the floating piston 124 will move the auxiliary piston only after the floating piston 123 and sliding piston 122 have completed their rightward movement. To retract the jack, fluid is admitted to the right of sliding piston 122 through a connection 117. In another form, the cylinder houses a normal sliding piston which enters from one end of the cylinder and an auxiliary piston of smaller diameter than the cylinder which extends into the other end of the cylinder. To extend the jack, fluid is admitted just in front of the auxiliary piston and causes a small relative movement between the latter piston and the cylinder until the auxiliary piston is as far from the end of the cylinder as its short piston rod will allow, whereupon the sliding piston moves rightwardly until it comes to rest against the end of the cylinder, after which the load is reduced by the cylinder moving rightwardly until the auxiliary piston abuts its end of the cylinder. In a further form. the left hand end of the cylinder, which contains a sliding piston and piston rod, is formed as a piston with two diameters which slide in a similarly bored end cap. In a final form, the jack is extended by admitting fluid through a connection 37, Fig. 6, to act upon the annular area of a sliding piston 39, which fluid at the same time moves the jack cylinder 38, until an' auxiliary piston 46 on a central tube 43, that extends axially through the cylinder into the piston rod of the sliding piston 39, abuts a shoulder 44 either in a cylinder closing cap or on an extension of the auxiliary piston exterior to the jack cylinder. When the rightward movement of the sliding piston 39 has been completed, pressure fluid acting on the annular area of the auxiliary piston 46 completes the final movement of the jack. In an emergency, the jack may be extended by an alternative source of pressure acting through a connection 36 whilst it may be retracted by admitting fluid through a connection 42. Specification 652,103 is referred to.