TENSION ADJUSTING DEVICE FOR CATERPILLER

PURPOSE:To eliminate the need for an accumulator, reduce the cost, and improve the safety of inspection and maintenance in a working machine with a caterpiller such as a hydraulic crane by setting the relief pressure that controls the exhaust of liquid for buffering variable according to the move of an adjusting cylinder. CONSTITUTION:A variable relief valve 30 is provided between the pressure receiving chamber 8 of an adjusting cylinder 6 and a tank 14 and determines the internal pressure of the pressure receiving chamber 8. By the sliding of the piston 28 of a pressure receiving box 28, the spring 29 of the variable relief valve 30 expands and contracts and the relief pressure becomes variable. An oil path 31 guides the pressure that operates the variable relief valve 30. The oil for buffering of the pressure receiving chamber 8 of the adjusting cylinder 6 passes through an oil path 9 and a duct 10 and is introduced to the variable relief valve 30. A piston 28, variable relief valve 30, and pressure switching means comprise a relief pressure change means that controls the exhaust of oil in the adjusting cylinder 6 according to the move of the adjusting cylinder 6.