Drift-prevention valve device, blade device, and working machine

A drift-prevention valve device mounted on a fluid-pressure cylinder configured to actuate an actuated unit by being extended/contracted by supply/discharge of working fluid from a control valve to a first fluid chamber for supporting operation of a machine body by the actuated unit and a second fluid chamber opposed thereto, the drift-prevention valve device comprising:

• a nonreturn valve including an accommodation part configured to communicate between the control valve and the first fluid chamber of the fluid-pressure cylinder, a valve element movably accommodated in the accommodation part, and an urging member for urging the valve element in a valve closing direction, configured to allow a flow of working fluid from the control valve to the first fluid chamber of the fluid-pressure cylinder and check the flow of the working fluid in the reverse direction;
• a piston accommodation part provided separately from the accommodation part of the non-return valve;
• and
• a power piston movably accommodated in the piston accommodation part, configured to define in the piston accommodation part, a first piston chamber communicating with the second fluid chamber of the fluid-pressure cylinder and a second piston chamber for draining located on the valve element side of the nonreturn valve and communicating with the tank, and further connected to the valve element of the non-return valve, and further connected to the valve element of the non-return valve, and operable by a difference between an urging force of the valve element by the urging member of the nonreturn valve and a second fluid chamber pressure of the fluid-pressure cylinder.