Patent GB-771396-A (GB)
Title: Improvements in or relating to hydraulic systems for tractor power-lift mechanisms
IPC: A01B63/10
Filed: 1955-03-18
Abstract: 771,396. Tractor power-lift mechanisms. FORD MOTOR CO., Ltd. March 18, 1955 [March 19, 1954], No. 8007/55. Class 79(1). In a tractor power-lift hydraulic system having a ram 24 and a double acting ram 16, each associated with a control valve 26, 18 whereby in the " lower " position of its valve the ram and the output of a pump 10 are connected to a sump 11, in the " neutral " position of the valve the pump output by-passes the ram to the sump and in the " raise " position of the valve the pump output is connected to the ram, the connection between the ram 24 and the sump 11 passes a valve element 18a in the control valve 18 of the ram 16, whereby concurrent operation of the control valves to the " raise " or " lower " positions produces only " raising " or " lowering " of the ram 16 until the valve 18 is returned to its " neutral " position. As shown the ram 24 is arranged at the rear of the tractor and the ram 16 and another double acting ram 17 controls forwardmounted implements. The valve 26 is controlled from a manual lever 29 and a draft link 31, the ram 17 being controlled by a valve 19 and the valves 18, 19 being actuated by manual levers 20. The pump 10 discharges to a pipe 13 having a pressure-relief valve 14 and the pipe 13 is connected to branches 13a, 13b through a flow equalizer valve 15. Each branch 13a for example, is connected to parts 18e, 18f in the control valve 18. With the control valves 18, 19 in their neutral positions shown in Fig. 1 liquid passes through the valves and pipes 13c, 13d to a pipe 13e. Movement of each control valve, 18 for example, to the right or left causes pressurized liquid to act on one side or the other of the element 18a thereby opening valve checks 18l, 18m to admit pressurized liquid to one side of the ram and connecting the other side to the sump through one or other end of the valve 18. The pipe 13e connects pressurized liquid to a port 21k of a low pressure relief valve 21 and to a check valve 22. The port 21k normally admits liquid to a space 21e in a movable piston 21c, pressure in the space 21e unseating a spring- urged valve 21f to connect the pipe 13e to the sump. The space 21e is also normally connected by a pipe 33 to a space 26m in the control valve 26. Movement of the control valve 26 to the left brings a portion 26g to the left of a space 26f thereby connecting pipe 13e to pipe 32 through the pipe 33 and pressurized liquid passing to the top of the piston 21c to move the piston downwardly to disconnect the pipes 13e, 33 from the space 21e. This disconnection causes pressure to build up in the pipe 13e sufficient to open the check valve 22 and permitting liquid to pass through a pipe 25 to the ram 24, but this flow is stopped if the elements in the valves 18, 19 are not in their middle positions. With the control valve 26 in the position shown in Fig. 4 a portion 26d is clear of a space 26c whereby a branch 23 of pipe 25 is connected to the sump through the open end of the bore 26e of the valve 26 and exhausting the ram 24. In this position of the valve the pipe 32 is also connected to the sump through an axial passage 26k in the valve spindle to permit upward movement of the piston 21c by means of a spring 21g.