GB654191A - Improvements in or relating to hydraulic jacks, presses and like hydraulic apparatus - Google Patents

Abstract

654,191. Lifting-jacks. LAYCOCK ENGINEERING CO., Ltd. July 12, 1949, No. 18643/48. [Class 78 (iii)] [Also in Group XXIX] In hydraulic jacks, presses and like apparatus of the kind provided with two pistons actuated by the same pump, the smaller of which is moved first with a rapid motion either to bring the load engaging member into engagement with the load, or to raise a light load, and the larger of which is moved after the completion of the quick lift to raise a heavy load, a passage for fluid is provided between the cylinders of the two pistons which is closed against the low pressure producing the quick lift by a non- return valve actuated by a spring-loaded plunger provided with a piston that is exposed to the high pressure continuously exerted on the larger piston when the valve has opened under increase of pressure at the end of the quick lift, the increased pressure maintaining the spring compressed and relieving the pump from having to overcome the spring for the opening of the non-return valve at each stroke of the pump. The lifting member 3, Fig. 1, is pivoted at 6 between side frames 1 and pivoted at 8 to a rod 9 extending from the main piston rod 10 of the cylinder portion 11 of the jack. The operating handle 12 is pivoted at 13 to the framework and an arm 14 on it is connected by a link 15 to the cross-head 16 of a pump plunger 17. The pump cylinder 29, Fig. 2, is mounted in a valve chest 24 which is welded to the end of a cylinder 19 in which works the larger piston 18 formed integral with the rod 10. The cylinder 19 is surrounded by a square tube 20. Oil contained in the space 21 between the parts 19, 20 can pass into the space between the parts 10, 19 through an aperture 22. A passage 25, Fig. 5, connects the space 21 to a passage 26 containing a filter 27 through which oil is sucked by the plunger 17 into the passage 28 leading to the pump cylinder 29 via a non-return ball suction valve 30 and passage 31. On the return stroke of the plunger oil is forced through the passage 31 past the non-return ball delivery valve 32 and through passage 33 into the cylinder 34 containing the smaller piston 35. This piston slides in a tube 36 which is fixed in the cylinder 34, has one end reduced at 37 to permit oil flow and extends freely into a bore 39 in the piston rod 10. Since the pressure exerted on the piston 35 is insufficient to move the crutch 4 after it engages the load, except for a very light load, continued operation of the pump handle builds up pressure until a spring- loaded ball non-return valve 41 is lifted against a spring 42 to permit oil to pass through a passage 43 to act on the piston 18. When this occurs since the plunger 46 which forces the ball valve 41 towards its seat carries a piston 47, once the ball is raised, the piston 47 is subjected to the pressure prevailing behind the piston 18 and the spring 42 is compressed and ceases to have any influence on the ball. When the load is to be lowered the needle valve 50, Fig. 2, is actuated to put the cylinder 34 in communication with the passage 51 leading to the passage 26 and space 21, the oil behind the piston 18 escaping by the passage 44 past the non-return ball valve 52 to the passage 53 which is a continuation of the passage 33. The needle valve 53A loaded by a spring 54 permits liquid under excess pressure to pass by.passages 55, 56 to space 21. Any oil which leaks past piston 47 returns to space 21 through a continuation 57 of the passage 55. The release valve 50 is connected by a universal joint 58 to the rod 59 which extends centrally of the handle 12 to a knob 60. This rod has a pin-and-slot connection with one member of the joint to permit relative longitudinal movement. A rod 66, Fig. 3, lying alongside rod 55 is moved by a knob 65 to insert a plunger at its lower end into any one of a series of holes in the valve chest to retain the handle in any desired position. In a modification, Fig. 9, the bore 76 of the auxiliary piston 75 communicates by the passage 77 with the bore 78 in the piston rod 10 and hence with the space behind the piston 18. The bore 76 is normally closed by the needle valve 80 which opens when the needle valve 50 is released to put the cylinder 34 into communication with the space 21 by the passage 51.