GB1314389A - Pilot operated control valve - Google Patents

Abstract

1314389 Valves KOEHRING CO 14 July 1970 34136/70 Heading F2V A control valve having a fluid-actuated spool 5 which can be moved in one direction (to the right) by fluid pressure exerted on one portion 19 thereof with fluid escaping from a pressure chamber 22 associated with another portion 20 of the spool, is characterized by vents 40 which can be rendered ineffective as a consequence of movement of the spool 5 so as to prevent further movement of the spool, and a stop 41 associated with the chamber to vary the extent that the spool moves before rendering the vents 40 ineffective. As shown, the control valve is in the neutral position the pressure in line 14 being exerted equally on the ends the spool 5 through bores 25 and 23. Movement of the pilot valve 9 to the right connects the pump to a chamber 26 and the resulting pressure difference on the spool 5 moves it to the left. The motor 7 is then connected to the supply line 15. Movement of the pilot valve 9 to the left (Fig. 2, not shown) places chamber 26 in communication with the reservoir and the resulting pressure difference on the spool 5 moves it to the right. When the spool 5 has moved to close off the vents 40, fluid is trapped in the chamber 22 bringing the spool to a halt. The speed of lowering of the motor determined by the extent of opening of grooves 43 is therefore adjustable by the screw 41. The motor may be double acting (Fig. 3, not shown). Both the rate of hoisting and the rate of lowering may be similarly controlled (Fig. 4, not shown). The vents 40 may be axially spaced each controlled by a shut-off valve (Figs. 5 and 6, not shown).