GB943869A - Hydraulic device - Google Patents

Abstract

943,869. Tractor power-lift mechanisms. H. MOLLY. Dec. 20, 1961 [Dec. 27, 1960; Jan. 10, 1961], No. 45667/61. Heading A1P. An automatic draft, hydraulic control device for a tractor comprises a continuously acting pump supplying through conduit 1 a slide valve 4 which has a throttling portion 15 for the pressure fluid before passing it through a non-return valve 3 to a ram. A by-pass conduit 10 connects the pump to an outlet 9 and is controlled by a spring loaded valve 11 connected with pressure fluid on its reverse side by a conduit 13 which allows differing pressures to reach the valve for different positions of the slide valve 4 whereby a minimum amount of pressure fluid passes through the throttling point 15. In the position shown in Fig. 3 the ram is held in position. Movement of the slide valve to the right or left in consequence of variations in draft load operates or retracts the ram respectively. In the constructional embodiment shown in Fig. 6 the valve 11 is incorporated in the slide valve 4 and is shown in the open position in which the pressure fluid delivered through conduit 1 follows the arrows to the exhaust conduit 9. In this position the slide valve 4 holds the ram 14 against movement. When the slide valve is moved to the right, pressure fluid is fed through passage 13 to the reverse side of the valve 11 to close it whereby the fluid is then fed through the throttling point 15 and the non-return valve 3, which is also incorporated in the slide valve, to the ram 14. In the fully closed position of the valve 11 all the pressure fluid is diverted to the ram whereas in a partially closed position holes 41 in the valve 11 allow an escape of fluid to exhaust thus providing a slower lift. A stop 53 on the ram engages a rod 49 just before the valve reaches an end position and the other end of the rod is therefore moved to operate the slide valve to release pressure from the ram. A safety valve 44 is incorporated and has associated with it a balancing piston 57. From the safety valve pressure fluid is fed along conduit 43 to chamber 46 to operate the slide valve to allow the pressure fluid to exhaust. The holes 41 in the valve 11 are so arranged that fluid passing therethrough causes the valve to rotate. A device for controlling a double acting piston associated with rod 14 is also described.