END SEAL

The invention relates to face seals of the rotors of pump units for separation of media or pressure drop. The invention can be used in the pumps used in nuclear power plants, in particular the main circulation pumps. The invention is aimed at improving the reliability of the assembly, as well as improving the workability of the parts and seal assembly. To obtain the appropriate technical results, a multistage face seal design is proposed, which comprises mounted in series work stages and end stage, each of which includes a rotor element located on the shaft and a spring-assisted axially movable stator element contacting it, sealed relatively to the casing with an O-ring, at the same time the cavities of high and low pressure of work stages are connected in series with restricted openings made in the stator element, which is designed so that to fulfill the functions of an axially movable step-like piston sealed relatively to the casing. The outer diameters of the stator element piston stages are made with the ratio D 2 = D 1 2 ˆ’ D 0 2 1 ˆ’ k k , where D 2 is the diameter of the larger piston cylinder, D 1 is the diameter of the smaller piston cylinder. This ratio ensures that there is no additional force on the stator element in the case of its normal operation, while allowing, in the case of seal opening, to increase the influence on the stator element aimed at seal closing due to the hydrostatic forces acting on the piston.