| 摘要 |
PURPOSE:To adapt the titled device for loads of various magnitudes by a method wherein a flow quantity control valve of a bleed-off valve for control of an actuator speed is opened at a neutral position of a directional control valve and a relief valve is controlled so that it is made into a high pressure relief valve at the time of starting and a low pressure relief valve at the time of stoppage. CONSTITUTION:A pilot port 2 which is on an energizing side for valve closing of a flow quantity control valve 1 is connected always with a return oil duct 3. A low pressure side oil duct between a directional control valve 4 and an actuator 5 is made so that it is changeable through pilot pressure from a high pressure side oil duct between the directional control valve 4 and the actuator 5 by providing a directional control valve of hydraulic pressure 7 so as to connect it with a pilot port 6 on an energizing side for valve opening of the flow quantity control valve 1, and a valve 11 which is opened and closed in a selective state is inserted between a cylinder chamber 9 and a hydraulic oil feed duct 10 so as to change setting pressure of the relief valve 8 to either high or low pressure. |
