| 摘要 |
PURPOSE:To lessen the pressure loss of control valves by providing a means to flow pressure oil discharged to the supply side when the potential energy of an actuator is released and also a control means to lessen the discharge amount of a variable capacity type oil-pressure pump. CONSTITUTION:When lowering a boom accompanied with the release of potential energy, the oil pressure of an auxiliary pump 18 reaches a direction switching valve 28 incorporated with a check valve on the one hand and reaches the second direction switching valve 29 on the other when a control valve 10 is switched toward right-handed position R by a lever 10a. Since the valve 28 is switched to the position D and the valve 29 is to the position U, the pressure oil reaches a servo cylinder 14. A capacity-varying mechanism 8 is also driven by pushing up the pump 15 and the discharge amount of the variable capacity type oil-pressure pump 7 is made smaller. The boom 1 lowers down under its own weight, and thereby the pressure oil is discharged through a pipeline 24 and the control valve 10 from a boom cylinder 4 to an oil tank 11. The pressure oil in the pipeline 24 flows through the check valve 28b into the pipeline 23. The amount of oil is not, therefore, reduced even when the discharge amount of the pump 7 is reduced. |
