| 摘要 |
PURPOSE:To prevent the occurrence of undesirable confined pressure by a method in which the spool of a counter balance value is divided into two, the third pilot chamber is formed in a faced manner, the higher pressure side of the pressure of the main circuit is selectively supplied to the chamber, and a control valve is specifically led to the spool of open center. CONSTITUTION:The first and second pilot chambers 9a and 9b introducing the pressure of the main circuit are provided between a traveling motor 2 and a drive control valve 30. The spools 8a and 8b of a counter balance valve 7 are operated by pressure oil in the chambers 9a and 9b. The third pilot chamber 20 is provided in the face of the counter ends of the spools 8a and 8b. A throttle 22 is provided between a shuttle valve 21 provided between the inlet pots 10a and 10b and the chamber 20, and the higher pressure of the ports 10a and 10b is selected by the valve 21 and transmitted to the chamber 20. The open center spool is provided for the control valve 30, and the entrance ports 30d and 30f are led to the outlet port 30c through the throttles 25a and 25b by the valve 30. |
