| 摘要 |
PURPOSE:To uniformize the holding force of a boom by keeping the pressures of two first pressure chambers uniform by a method in which the first throttle valve is provided in a pipeline connecting the first pressure chambers and also the second throttle valve is provided in a releasing pipeline connecting said pipeline and said valve. CONSTITUTION:Pressure oil is supplied to the first pressure chamber 16 to extend a rising and falling cylinder 13 for raising a boom. Also, pressure oil is supplied to the second pressure chamber 19 to contract the cylinder 13 for bringing the boom to falling. On both ends of the first pressure chamber 16 side of a pipeline 32 connecting the first pressure chambers 16, the first throttle valve 33 to close the pipeline 32 when the pressure difference between the front and rear sides in the pipeline 32 becomes more than a given value but to keep the pileline 32 in communicating state usually is provided. Also, in a drain releasing pipeline 35 connecting the pipeline 32 with the valve 33, the second throttle valve 36 to open the pipeline 35 in usual case but to close the pipeline 35 when the pressure difference between the front and rear sides in the pipeline 35 becomes more than a given value is provided. The pressures of two first pressure chambers 16 can thus be equalized and the holding force of the boom can be made uniform. Also, the pressures of the first pressure chambers 16 can be uniformized even by breaking the pipeline 32. |
