System separator, comprising a backflow preventer having 1.1 a housing enclosing a main flow conduit, wherein an inlet and an outlet are provided in the housing; 1.2 a valve seat inside the housing on the main flow conduit; 1.3 a valve body which is movable relative to the valve seat in order to close off the main flow conduit together with the valve seat in a closed position and to release the main flow conduit in an open position; wherein 1.4 the valve body is alternately movable between its closed position and its open position by a pressure difference in the main flow conduit and/or by the force of a spring element; wherein 1.5 the main flow conduit is divided in the area of the valve body into at least one outer flow conduit and one inner flow conduit, and 1.6 the valve body encloses the inner flow conduit and forms at least one valve-body valve seat on the inner flow conduit and comprises at least one primary and one secondary valve disk (4.1, 4.2), wherein the valve body comprises a valve rod which carries the primary valve disk (4.1) and on which the secondary valve disk (4.2) is slidably positioned; and 1.7 the valve rod is mounted in a star-shaped bearing support or bearing cross in the main flow conduit, and 1.8 the valve disks (4.1, 4.2) are arranged in such a way that in the closed position the primary valve disk (4.1) is in sealing contact with the valve seat on the main flow conduit and the secondary valve disk (4.2) is in sealing contact with the valve-body valve seat on the inner flow conduit, and in the open position the primary valve disk (4.1) is lifted off the valve seat on the main flow conduit and releases the outer flow conduit, and the secondary valve disk (4.2) is lifted off the valve-body valve seat on the inner flow conduit and releases the inner flow conduit, characterized in that 1.9 a discharge outlet is provided in the housing, which is connected to the outlet in a flow-conducting manner in the closed position of the valve body and is sealed with respect to the main flow conduit in the open position of the valve body; wherein 1.10 the discharge outlet is provided in one or more radial struts of the star-shaped bearing support or bearing cross. 1.1 a housing enclosing a main flow conduit, wherein an inlet and an outlet are provided in the housing; 1.2 a valve seat inside the housing on the main flow conduit; 1.3 a valve body which is movable relative to the valve seat in order to close off the main flow conduit together with the valve seat in a closed position and to release the main flow conduit in an open position; wherein 1.4 the valve body is alternately movable between its closed position and its open position by a pressure difference in the main flow conduit and/or by the force of a spring element; wherein 1.5 the main flow conduit is divided in the area of the valve body into at least one outer flow conduit and one inner flow conduit, and 1.6 the valve body encloses the inner flow conduit and forms at least one valve-body valve seat on the inner flow conduit and comprises at least one primary and one secondary valve disk (4.1, 4.2), wherein the valve body comprises a valve rod which carries the primary valve disk (4.1) and on which the secondary valve disk (4.2) is slidably positioned; and 1.7 the valve rod is mounted in a star-shaped bearing support or bearing cross in the main flow conduit, and 1.8 the valve disks (4.1, 4.2) are arranged in such a way that in the closed position the primary valve disk (4.1) is in sealing contact with the valve seat on the main flow conduit and the secondary valve disk (4.2) is in sealing contact with the valve-body valve seat on the inner flow conduit, and in the open position the primary valve disk (4.1) is lifted off the valve seat on the main flow conduit and releases the outer flow conduit, and the secondary valve disk (4.2) is lifted off the valve-body valve seat on the inner flow conduit and releases the inner flow conduit, characterized in that 1.9 a discharge outlet is provided in the housing, which is connected to the outlet in a flow-conducting manner in the closed position of the valve body and is sealed with respect to the main flow conduit in the open position of the valve body; wherein 1.10 the discharge outlet is provided in one or more radial struts of the star-shaped bearing support or bearing cross.