To improve starting property of an engine by reducing load of a hydraulic pump in starting the engine when temperature is low in a hydraulically driven device of a construction machine.
A manual forcible switching means for forcibly switching an unload valve 9 to be in an open state is composed of a hydraulic piston device 20, a gate lock valve 23, and a gate lock lever 24. The hydraulic piston device 20 includes a piston 26 equipped with a piston rod 25, a spring 27, an oil chamber 20b, and a pressure receiving part 28. The oil chamber 20b is connected to a pilot oil passage 3b via an oil passage 22. When the gate lock valve 23 is at a lock-releasing position, discharged oil of a pilot pump 3 is introduced to the oil chamber 20b, and a force of the spring 27 for pushing a valve spool 51 of the unload valve 9 to the opening direction is released. When the gate lock valve 23 is operated at a locking position, the valve spool 51 of the unload valve 9 is pushed to the opening direction by the force of the spring 27 so as to forcibly switch the unload valve 9 to be in a fully open state.
TAKAHASHI KIWAMU
TAKEBAYASHI KEIFUMI
MORI KAZUSHIGE
| JP2007046712A | 2007-02-22 | |||
| JP2002089506A | 2002-03-27 | |||
| JPS6386385U | 1988-06-06 | |||
| JPH08100448A | 1996-04-16 | |||
| JP2007270847A | 2007-10-18 | |||
| JPH11315805A | 1999-11-16 | |||
| JPH04191502A | 1992-07-09 |
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