| 摘要 |
<p>1,098,310. Valves. HYDRAULIC UNIT SPECIALTIES CO. Feb. 14, 1966 [June 16, 1965; Sept. 21, 1965], No. 6424/66. Heading F2V. [Also in Division F1] Each valve of a bank of valves has a spool valve 7 slidable in a bore 6 intersected by a pair of exhaust ports 17, working ports 9, 10 feeder ports 14, 15 and an open-centre supply port 11. The feeder ports 14, 15 are in communication through a check valve 16 and the port 14 opens into the supply port 11 upstream of the bore 6; the port 11 has upstream and downstream sections connected to adjacent valves, which sections are in communication when the spool is in the neutral position only; in any other position the communication is prevented and fluid is supplied to the required working port from port 14 or 15. The working ports 9, 10 are connected to the rod and head end of a jack 8 and the spool has a " slow " and " fast " lower positions; " slow " lowering is effected by passing the fluid from the jack head-end to exhaust via a restricted passage 20 in the spool; the passage 20 is removed from the path of the exhaustive fluid during " fast " lowering. " Fast " lowering is prevented by a stop if the jack is heavily laden, the higher exhaust pressure resulting therefrom being sufficient to move a piston 26 within the spool 7 to the right against an adjustable spring causing a cam 32 to urge balls 22 radially to engage shoulder 25 so preventing further right-ward movement of the spool. Inward camming of the balls by the shoulder 25 also provides the operator with an indication by " feel " when he moves the spool into the " fast " lower position, such as when the jack is lightly or moderately loaded. In another form (Fig. 4, not shown), the valve has both " fast " and " slow " raise positions and the stop is operative during either " fast " raise or lower if the jack load is heavy. In the " fast " raise position a regenerative action is provided by using the fluid exhausting from the rod end to augment that supplied by the pump to the head end. The stop device may be connected by external passages to the jack, and the device may operate in the neutral position only of the valve.</p> |
