| 摘要 |
PURPOSE:To make a spool unmovable to one side from a central position by providing a piston cylinder on a side of the spool of a main valve, and said piston is actuated to touch the edge of the spool. CONSTITUTION:A cylinder chamber 31 is provided on a main body 23 of a main valve 4 and a step piston 32 for a stopper, to which a spring applied by a spring 33 is provided in the interior of the main body 23. A port 35 of the cylinder chamber 31 provided with a cam valve is connected with a pressure source 45 through a pilot line 52. When the cam valve 3 is located at a symbol position S1, a hydraulic fluid is led into it, the step piston 32 is moved to the right, and an edge face 40a of a medium diameter part 40 of the step piston 32 touches a partition wall 41. Then, even if a solenoid 5a of solenoid directional control valve 4 is electrified, a spool 25 can not be moved to the left from a central position, as a small diameter part 38 of the step piston 32 is protruded into a spring chamber 26b. |
