Hydraulic drive unit

A hydraulic drive unit for driving a hydraulic actuator including a pair of supply-discharge ports, the hydraulic drive unit comprising:

• a pump including a casing, a pair of pump ports, and an air vent port from which air in the casing is discharged to an outside of the casing together with hydraulic oil;
• a pair of supply-discharge lines that connects between the pair of pump ports and the pair of supply-discharge ports;
• a valve block that incorporates at least one valve therein, the at least one valve being provided on the pair of supply-discharge lines and/or oil passages connected to the pair of supply-discharge lines;
• a sealed tank that is connected to the pair of supply-discharge lines, the sealed tank storing the hydraulic oil;
• a suction line that leads the hydraulic oil in the sealed tank to the pump;
• a connecting line that connects the air vent port to the suction line;
• a gas-liquid separator that separates the air and the hydraulic oil flowing through the connecting line from each other, the gas-liquid separator supplying the separated hydraulic oil to the suction line while releasing the separated air from the connecting line,
• a frame to which the pump and the valve block are mounted;
• and
• a tank support mechanism that supports a bottom portion of the sealed tank from below;
• wherein
• the pump is disposed upward of the valve block and the sealed tank in a vertical direction;
• the sealed tank is disposed such that a hydraulic oil inlet/outlet of the sealed tank faces upward, and such that the sealed tank is mountable to and detachable from the frame without disassembling a framework of the frame;
• the tank support mechanism includes:
• a fixing member fixed to the frame, and
• a movable member that is movable in an upward and downward direction relative to the fixing member;
• and
• an upper end portion of the movable member contacts the bottom portion of the sealed tank from below.