Piston-type compressor

A piston-type compressor for gaseous media, e.g. a brake air compressor for automotive vehicles, particularly a compressor having capacity control means, is provided with an externally arranged lubricant pump for supplying the lubricant from a storage reservoir which is positioned below the compressor to a lubrication circuit of the compressor. A downwardly extending return line for the lubricant is provided between the otherwise enclosed crankcase of the compressor and the storage reservoir. In order to prevent a build-up of superatmospheric pressure in the crankcase, a self-acting check valve is installed in the return line the check valve serving to block flow of lubricant through the return duct toward the crankcase of the compressor.