NDC NWAV-1 Alarm Check Valves are swing type waterflow alarm check valves intended for use in automatic wet-pipe fire sprinkler system. They activate the fire alarm via the pressure-actuated alarm switch when the water that is flowing into the system is equivalent to the discharge from one or more sprinklers. With the clapper having rubber facing that sits well with the seat ring, they also prevent water backflow when the water supply is stopped. They can also be fitted with a separately ordered retard chamber for installations subject to variable pressures. The retard chamber provides suitable time delay in order to eliminate potential false alarms due to surges or fluctuating water supply pressures. These Alarm Check Valves are intended to be installed in vertical orientation only.