| 摘要 |
<p>PURPOSE:To secure the distributed discharge oil quantity to a boom cylinder properly and surely and to improve the safety and workability by automatically operating a variable flow control valve disposed on the inlet side of a revolving selector valve through a pilot operated directional control valve. CONSTITUTION:A variable throttle valve 62 forming a variable flow control valve is provided on the inlet side of a revolving selector valve 24, and a pilot operated directional control valve 66 is disposed in an oil path 64 communicating the throttle valve 62 with the first hydraulic circuit 14. During boom operation, the signal pressure of a signal circuit 50 operates the pilot operated directional control valve 66 through a signal oil path 68, and the discharge pressure of the first driving pump 10 is applied to a variable operation pressure receiving portion 62a of the throttle valve 62 through the oil path 64. Further, when the boom rising load pressure amounts to a designated value, the throttle valve 62 is operated against a return spring 62b to limit the quantity of oil supplied to a rotating motor 22, so that the quantity of oil supplied to a boom cylinder 26 is secured so as to keep the turning operation from preceding.</p> |
