Groco PNC Bronze Check Valve 

Unique cast bronze pipe nipples feature an efficient internal check valve which imposes almost zero flow restriction and requires less than 1/2 PSI to open. Colored bands indicate flow direction (green to red).
NOT TO BE USED WITH DIESEL FUEL, GASOLINE, OR IN POTABLE WATER SYSTEMS.

Pipe: 1/2" NPT", Length: 0.88