| 摘要 |
PURPOSE:To make safe the circuit by blocking a float selector valve through spring force even upon fracture of conduit communicating between pilot valve and float selector valve. CONSTITUTION:Upon bringing of pilot valve 19 to lifting position, pressure oil is fed to the right pressure receiving section 18 to bring a spool to the position IIthus to lift the boom 2. While upon bringing of the pilot valve 19 to intermediate position, the boom 2 will lower. Upon bringing to float position, the pilot pressure is applied directly onto the spool of float selector valve 25 to bring to the communicating position against a spring 45 thereby an unload valve 23 is released thus to communicate first outlet port 13 and inlet port 11 with drain T. Since the float selector valve 25 is blocked by the spring force 45 even upon fracture of conduit 47, the unload valve 23 will not open thus to block lowering of boom 2. |
