| 摘要 |
PURPOSE:To reduce the friction between a crawler and a crawler support section, by providing a pilot type check valve which uses the pressure upstream of a selector valve as a pilot pressure so that a closed condition is sustained to set the tension of the crawler at an optimum value. CONSTITUTION:A pilot check valve 16 is operated by the pressure upstream of a selector valve 14 as a pilot pressure and is therefore opened to communicate a rod side chamber B with a tank 11. Further, hydraulic oil from a hydraulic pressure source 6 is led into a head side chamber A through a pressure reducing valve 7, a pipe line 8 and a check valve 9 so that a piston 2 is pushed out by the pressure set at the pressure reducing valve 7 and the spring force of a spring 3 while hydraulic oil in the rod side chamber B is discharged from a tank 11 through the valve 16 which is opened by the pressure upstream of the selector valve 14. Accordingly, an idler is displaced to stretch the tension of a crawler 5 so that the set pressure is obtained, and therefore, the valve 14 is changed over to balance with the pressure in the rod side chamber B due to the valve 15.
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