Economical and reliable in-tank check valves for use on compressors or water, oil and gas tanks. For industrial and commercial applications. VIK's have female National Pipe Thread (NPT) inlets and male NPT into tank. All have tapped 1/8" FPT ports for unloader, with removable plugs. Inlets on No's. 6X213, 6X214, 6X215 and 6X216 are threaded to accept compression fitting, eliminating need for an adapter for pipe thread-to-compression fitting thread