A balanced bottom valve

A balanced bottom valve for emptying and filling a liquid tank, particularly a fuel tank and more particularly the fuel tank of a gasoline truck, through an opening in the bottom of the tank. The valve is placed inside the tank adjacent its bottom opening and includes a valve seat (314) which defines a throughflow opening, a valve plate (320) which can be moved to and from a seat shielding position, spring means (341, 342) which function to bias the valve plate (320) to a closed seat sealing position, and a fluid-driven piston-cylinder unit (330, 323, 324) which functions to lift the valve plate (320) against the force of the spring means (341, 342) when activated. The unit includes a cylinder (323, 350) which houses a piston (330) which is firmly connected to a rod (313). The bottom valve is characterized in that the rod (313) extends through the valve plate (330) and is fixedly mounted so that the valve plate (320) is sealingly connected with the cylinder mantle; in that the spring means (341, 342) acts between the valve plate (320) and the piston firmly connected to the rod (313) of the piston-cylinder unit; and in that the valve is located inside the tank.