The Bendix® ST-4™ safety valve protects the air brake system against excessive air pressure build‑up. The valve consists of a spring-loaded ball valve subjected to air pressure which will permit air to exhaust to atmosphere, if the air pressure rises above the valves pressure setting. This safety valve is recommended for use in charging systems and compressors with a discharge line. The discharge line safety valve is installed in the compressor cylinder head or close to the compressor discharge port. It protects against over pressurizing the compressor head in the event of a discharge line blockage downstream of the compressor. Excessive air pressure will cause the safety valve to unseat, release air pressure and give an audible alert to the operator.