| 摘要 |
PROBLEM TO BE SOLVED: To prevent a main switch valve from being set in a neutral position (all port open state) when a piston is operated at a very low speed, in a piston reciprocation type hydraulic pump driven by pressure air.SOLUTION: First and second annular valve faces 51, 52 brought close to or into contact with first and second annular valve seats 53, 54 at valve cases 31 and 32 sides, are formed on upper and lower both ends of an annular valve element body 43a of a main valve element 43, an air introduction chamber 55 is formed by a piston accommodation hole 45 and a piston portion 46, and an auxiliary switch valve 42B switches a main switch valve 42A between an air supply position and an air discharge position by supplying and discharging the pressure air to the air introduction chamber 55. A center-side core part of the main valve element 43 is constituted as an independent auxiliary valve element 43A, its upper end faces an air discharge port 5, and the auxiliary valve element 43A is rapidly moved by weak pressure air force, to release shielding of a second valve member 57 and to reliably switch the main valve element 43 to be operated. |
