By at least a pair of end face perpendicular to the rotation axis, the liquid pressure and mechanical compensation with the cooperation of the action of the spring force and the auxiliary seal, keep post merger relative sliding up and prevent leakage of liquid device called a mechanical seal. When the mechanical seal works, the moving ring, under the action of compensating spring force, is attached to the stationary ring and is rotated with the shaft to form the friction pair bonding contact. medium to be delivered into the contact surface to produce a layer of liquid membrane, liquid membrane help prevent medium leakage, reduce wear and tear.