| 摘要 |
The valving means comprises a spool member (20) slideably mounted within the ram and having ports (13a) and (14a) therein adapted to register with co-operating ports (13) and (14) in the cylinder wall upon axial movement of the spool member (20) the spool member (20) being formed with a circumferential recess (21) therein which is adapted at substantially all positions of the spool member (20) to be in fluid flow communication with an inlet port (14b) and (14c) for fluid under pressure, there being formed at the end of the spool member (20) a chamber (30) adapted to be in fluid flow communication with fluid under pressure or with an environment at lower pressure whereby fluid under pressure can act on the end face (31) of the spool member (20), the effective radial area of the end face (31) of the spool member (20) exposed to the fluid being greater than the difference in effective radial areas of the two radial side walls (27) and (27a) of the circumferential recess (21), the effective radial area of that side wall (27) adjacent the end wall (31) of the spool member (20) being greater than the effective radial area of the other side wall (27a) of the recess (21), whereby application of fluid under pressure to the recess (21) is adapted to cause the spool member (20) to move axially with respect to the chamber (30) and application of fluid under pressure to the chamber (30) is adapted to cause the spool member (20) to move axially in the opposite direction. |
