Control valve for single-acting servo-motors, especially for power lifts in agricultural tractors

摘要

960,271. Fluid-pressure servomotor control systems. RHEINSTAHL HANOMAG A.G. Aug. 12, 1961, No. 29195/61. Heading G3P. [Also in Division F2] A valve controlling a single-acting ram, such as that of a tractor mounted agricultural implement, comprises a hollow closure-member 2 with an annular groove 7 slidable in a housing into which open supply and exhaust passages 3, 4, and two further passages 5, 6 leading, respectively, to the ram and either one or more further valves, not shown, for controlling other rams or exhaust. The member 2 is movable manually through a pinion 8 and a rack 9 formed on the member 2; a spring-loaded detent 10 coacts with the pinion teeth. To extend the ram, the member 2 is moved to the right to interconnect passages 3, 5; at the end of the ram stroke the supply pressure rises until it unseats a relief valve 12 to enable the supply fluid to act on the right end of the member 2 and move the latter leftwards against the action of the detent 10 until the member 2 is clear of a casing extension 16 whereupon the fluid flows to the exhaust passage 4 by the hollow bore 15 of the member 2. The relief valve 12 then reseats and the member 2 rests in the "hold" position wherein passage 6 is connected to the supply passage 3. Upon translating the member 2 further leftwards into the "lower" position, passages 3, 6 remain connected and passage 5 is open to exhaust passage 4 via the bore 15. With the member 2 in the "lower slowly" position i.e. still further to the left, the left end of the bore 15 co-operates with an extension on the adjacent end of the casing to throttle the fluid passing to the exhaust passage 4; this position is adjustable by means of a stop 17.