GB863701A - Control for hydraulic jack circuits - Google Patents

Abstract

863,701. Hydraulic apparatus. CATERPILLAR TRACTOR CO. June 29, 1959 [April 3, 1959], No. 22176/59. Class 69 (2). [Also in Group XXI] The lowering of an implement, such as the bulldozer 10 of a tractor 13, by a jack 14 is effected rapidly by the provision of a passage 24 which is between the intake and exhaust passages 19, 20 of the jack and has one or more check valves 26, 32 adapted to open upon the event of the pressure in the exhaust passage exceeding the pressure in the intake passage. The jack is supplied with liquid pressure from either of the passages 19, 20 which are connected to a reversing valve 18 leading from a pump 17 and sump 21. A housing 22 is interposed in the passages closely adjacent the jack and has passages 23, 24 forming part of the passages 19, 20 respectively. The passage 24 also extends to meet the passage 23 and is provided with the check valves 26, 27. When the bulldozer is being lowered, the pump 17 is connected by the passage 19 to the upper end of the jack. The weight of the bulldozer causes the pressure in the exhaust passages 20, 24 to be higher than in the intake passage to open the check valves 26, 27 and by-pass the fluid from the lower end of the jack to the upper end; a throttle 29 in a normally closed check valve 25 assists in the raising of the pressure in the passage 24. When the bulldozer strikes the ground, the drop in pressure in the passage 20 permits the check valves 26, 32 to close so that the fluid pressure from the pump applies a downward force on the bulldozer. The bulldozer is raised by operation of the valve 18 to connect the pump to the line 20, the pressure from the pump opening the check valve 25 to permit the fluid to flow unrestricted to the lower end of the jack. In other embodiments, the check valve 25 is dispensed with, the throttle being formed in the passage 24 and a single check valve is provided between the intake and exhaust passages.