Is a kind of special hydraulic oil as the working medium, through the hydraulic pump as the power source, through the pump to the hydraulic oil through the hydraulic line into the cylinder / piston, and then the cylinder / piston in a few groups of mutual cooperation with the seal, the sealing of different positions are different, but all play a role in sealing, so that hydraulic oil can not leak. Finally through the one-way valve to hydraulic oil cylinder / piston in the circulation work to complete a certain mechanical action as the productivity of a mechanical circulation in the tank.