US Patent 7694355 Pressure vessel

A pressure vessel at least includes a main vessel, an air entry valve, a water entry valve, a drain valve and a control valve. The drain valve is provided with a valve base set on the top of the main vessel, a piston unit inserted inside the valve base able to be moved upwards and a spring installed between the piston member and the valve base. In addition, the pressured water in the main vessel coming from the water entry valve and the air entry valve can be stored in the control valve and guided to a chamber between the piston unit and the valve base, enabling the piston member to surpasses the elasticity and the water pressure to move up to separate from a drain exit of the main vessel for flushing a toilet. Therefore, the present invention has a simple structure, easy to assemble, preventing accidental flushing.