A preflushing unit (10) preflushes a breathing gas circuit (210) of a closed-circuit respirator (200). A basic body (20) has an inlet port (22), feeding breathing gas from a breathing gas supply (220), an outlet port (24) discharging breathing gas into the breathing circuit, and a flow section (32) fluid connecting a valve chamber (30). A valve body (40) with a sealing surface (42) is arranged in the valve chamber (30). An elastomer body (50) with a counter-sealing surface (52) in the valve chamber, fluid tight separates the flow section from a control section (34). The counter-sealing surface acts with a sealing force against the valve body for sealing the flow section. A control port (26) of the basic body provides a controlled feed of breathing gas from the breathing gas supply into the control section for pressure equalization between the flow section and the control section.