| 摘要 |
[Problem] In a compressed air driven hydraulic pump (P), continuous reciprocating operation of a piston (14) is implemented by a main changeover valve (42A) that changes over a compressed air supply system, and by an auxiliary changeover valve (42B) that changes over the main changeover valve (42A) between an air supply position and an air discharge position; but in some cases the main changeover valve (42A) is in a neutral position (an all ports open state) when the piston (14) is operating extremely slowly. [Solution] First and second annular valve faces (51, 52) that approach closely or contact against first and second annular valve seats (53, 54) on valve cases (31, 32) are formed on both the upper and the lower ends of an annular valve body portion (43a) of a main valve body (43), an air intake chamber (55) is defined by a piston reception hole (45) and a piston portion (46), and the auxiliary changeover valve (42B) changes over the main changeover valve (42A) between its air supply position and its air discharge position by supplying compressed air to the air intake chamber (55) or discharging air therefrom. A center side portion of the main valve body (43) is made as a separate auxiliary valve body (43A). The sealing of a second valve member (57) is released by the auxiliary valve body (43A) being rapidly shifted with low pressure compressed air, and thereby the main valve body (43) is reliably changed over. |
