Portable hydraulically operated device incorporating automatic drain valve

A portable hydraulically operated clamping device comprising:

• a housing;
• a handle fixed to said housing for holding said portable clamping device;
• a single-acting cylinder carried by said housing and having a piston, a pressure chamber for applying hydraulic pressure to the piston to move the piston from an original position to an operated position, and a return spring for biasing the piston toward the original position;
• a clamping tool having at least one movable member operated by said piston for clamping a workpiece;
• a hydraulic pump incorporated in said housing, for delivering a pressurized fluid to be fed into said pressure chamber of said single-acting cylinder;
• an electric motor incorporated in said housing for operating said hydraulic pump;
• a switch carried by said handle, for turning on and off said electric motor, said switch being finger-operable while said clamping device is hand-held at said handle;
• means for defining a delivery passage for connecting said hydraulic pump and said pressure chamber of said cylinder;
• an oil reservoir including a bag-like elastic member for partially defining a variable-volume chamber in which the pressurized fluid delivered from said hydraulic pump is stored;
• a relief valve incorporated in said housing and connected to said delivery passage and operated when a pressure in said pressure chamber of said cylinder has reached a predetermined level;
• a check valve incorporated in said housing and disposed in a portion of said delivery passage between said pressure chamber of said cylinder and a point of connection of said relief valve to said delivery passage, said check valve inhibiting a flow of pressurized fluid through said delivery passage in a direction from said pressure chamber toward said hydraulic pump;
• and
• an operator-controlled shut-off valve carried by said housing and connected to one of said pressure chamber of said cylinder and a portion of said delivery passage between said pressure chamber and said check valve, said shut-off valve being manually operated to an operated position for discharging said pressurized fluid from said pressure chamber of said cylinder, said check valve and said shut-off valve maintaining the pressure in said pressure chamber of said cylinder at said predetermined level after said hydraulic pump is turned off, until said operator-controlled shut-off valve is manually operated to said operated position.