The Viking Model K-1 (threaded) and L-1 (grooved) Spring Loaded In-Line Check Valves are general purpose rubber-faced check valves approved for use in fire-service systems.  These valves, which are  manufactured with a brass body, brass seat, and a rubber-faced clapper assembly, may be installed vertically or horizontally.  The L-1 and K-1 valves are often used as a riser check valve in small deluge and preaction systems.