Abstract: A spring brake actuator (1) provides a service brake function and a parking brake function and comprises a housing (2) with a housing base (4). A compression spring (14) and a ram assembly (10, 11, 28) with a spring brake piston (28) are provided are provided in the housing (4). The ram assembly separates a spring chamber (12), in which the compression spring (14) is disposed, from a parking chamber (16). The spring brake actuator (1) includes a check valve (50), which is included in the ram assembly to allow an air flow to the parking chamber (16) in case of a compounding condition. The check valve (50) includes a one-way valve, for example a duckbill valve, and a supporting element for securing the one-way valve in the ram assembly.