Patent GB-590566-A (GB)
Title: Tripod jack
IPC: B66F3/24
Filed: 1944-11-21
Abstract: 590,566. Jacks. PAGE, H. E. Nov: 21, 1944, No. 23142. [Class 78(iii)] , A hydraulic jack comprises a central vertical load-engaging member which is moved by three inclined rams which are disposed symmetrically around and inclined towards it. A base 5, Fig. 1, is provided with a cylinder bore 7, fluid passageways 8, 9, 9a, 10 and 11, a reservoir 12, fluid chambers 14 and 15, a threaded socket 17 and a boss 18 to serve as a pivot for a pumping lever 20. A tubular guide member 25 screwed into the socket 17 acts as a guide for a vertically movable member 30, which is formed with a cylinder bore 33 and a smaller bore 32. A threaded bush 35 is screwed into the top of the body 30 and acts as a guide for a cylindrical member 37 in the upper end of which is mounted a threaded extension 39. A piston 45 reciprocates in the cylinders 32 and 7. The upper end of the cylinder 32, Fig. 3, is connected by a port 52 to the bore 51 of a valve housing 50. The lower end of the bore communicates with a reservoir 55 in the member 30 by a pipe 56 and screen 57. A poppet 60, with stems 61 and 62, and a spring-pressed ball valve 55 are contained in the bore 51. Three bifurcated bosses 80 are provided on the base to which the lower ends of three inclined cylinders 82 are attached. Pistons 86 and piston rods 87 are mounted in the cylinders, the ends of the rods being attached to three similar bosses 88 at the top of member 30. The lower end of each of the cylinders is connected with the base chamber 15 by means of a flexible hose 95 and the upper end of each cylinder with the reservoir 12 via a flexible hose 100 and a valve 101. The cylinder 33 also communicates with the reservoir 55, through a passageway 105 and a valve member 106, Fig. 4, the latter consisting of a housing 107 within a bore 108. A poppet 110 is slidably mounted in the bore of the housing 107, seated towards the reservoir by a spring 111. A safety valve is incorporated within the poppet and consists of a hollow plug 115, with a port 116 against whose periphery, another poppet 117 is seated by a spring 118, fluid being passable through the ports 119 and poppet 117. The housing 107 has a hollow extension 120 which lies below the fluid level. In operation, to bring the jack into contact with the object to be raised, the lever 20 is operated to reciprorate the piston 45. On each downstroke of the piston 45 fluid is drawn from the reservoir past the poppet 60 and into the cylinder 32 and on its upstroke the fluid pressure in the cylinder lifts the member 30 since the ball valve spring 63 is strong enough to resist low pressures and will not operate until the work is contacted. The cylinder 33 draws in fluid on its ascent via the passageway 105 and valve unit 106. At the same time the piston 45 draws fluid into the cylinder 7 from the reservoir 12 through the passageway 8, and ball valve 99 and on its downward stroke pumps fluid into the lower end of the cylinder 85. To maintain rigidity at high levels fluid may be trapped in the upper end of the cylinders 85 by closing the valve 101 thereby compressing any fluid present. Should it be desired to lift the load by raising the member 30 or member 37 only, a valve 137 is opened so that fluid is drawn from the reservoir 12 via the ball valve 99 and returned via the ball valve 136. To lower the jack, the valves 98, 101, and 130 are opened.