Description Boss check valves have been designed to work with all air compressors needing a 3/8NPT male to 3/8NPT female. They provide maximum resistance to prevent back pressure to the Air Compressor. What Is a Check Valve? A check valve is a critical part of any air compressor system. A check valve ensures that air can only flow one-way through it. In an air system it normally sits between an air tank and an air compressor and prevents tank pressure from leaking back through to the air compressor. Without this you may damage your compressor, it would also take much longer to fill your air tank and leave potential for leaks to occur in the system.