Automatically shuts off air flow upon a sudden air line break. Protects plant personnel and property from injury by "whipping" air hoses. Resets when repair is made. Allows full, unrestricted flow of air in normal open position. Meets OSHA Standard 1926.302(b)(7) for air hoses exceeding 1/2" ID requiring a safety device at the source of supply or branch line to reduce pressure in case of hose failure.