| 摘要 |
<p>PURPOSE: To prevent the falling of a car body when an engine is stopped under the state, in which the car body is lifted. CONSTITUTION: A relief valve 14 is mounted on a circuit 13 connecting the contraction side chamber 11 of a boom cylinder 6 for a hydraulic shovel and a directional control valve 12 for a boom, and relief set pressure is lowered when the contraction side chamber 40 of a cylinder 37 is supplied with pressure oil and relief set pressure is increased when the contraction side chamber 40 is communicated with a tank in the relief valve 14. The contraction side chamber 40 is supplied with the discharge pressure oil of an auxiliary hydraulic pump 20 driven by an engine 21 by a changeover valve 41, and the contraction side chamber 40 is communicated positively with the tank when the engine is stopped.</p> |
