| 摘要 |
A valve for controlling a hydraulic cylinder (26) for reversing the work stroke, comprises housing (1) containing a sliding spool (3) with a through bore (4, 4') containing a spring-loaded valve body (6) which co-operates with a seat (7) formed in the bore (4, 4') of the sliding spool (3), said slide (3) having recesses (5, 9, 22, 23) to co-operate alternately with channels in the housing when the sliding spool (3) has assumed one or the other end position. The valve seat (7) and/or the co- operating valve body (6) is formed to provide an imperfect seal, there being a relatively narrow open passageway between the two members, such that a flow of fluid under pressure through bore (4, 4') of the sliding spool (3), produces a pressure drop causing slide (3) to be moved from one end position to the other end position. Sliding spool (3) co-operates with a spring- loaded (16) piston (13) having a through bore (14) of substantially smaller cross section than the slide's bore (4, 4'), to act as a throttling passageway, the open end thereof in one end position of the piston (13) seating against a shoulder (24) on the valve housing (1) for closing off the throttling passage orifice, which causes the slide (3) to be returned to its starting position as soon as the flow of pressure fluid past the valve body (6) ceases. The valve is flow- controlled, requiring only a slight drop in pressure (2-3 bar) over the seat (7) in the through bore (4, 4') of the sliding spool (3) for holding the sliding spool (3) in one end position. <IMAGE> |
