Waterflow alarm valves (alarm check valves) are installed in either vertical or horizontal positions in wetpipe sprinkler systems to sound a fire alarm gong when a flow of water from the system equals or exceeds that of a single sprinkler. They are designed for use with hydraulic or electric gongs or both. There are two designs, the differential type and the pilot valve type. The differential type has a rubber-faced clapper with an annular groove in the seat; the pilot valve type has a metal-faced clapper with a pilot valve attached to the clapper arm. A retard chamber, which minimizes false alarms due to surges and fluctuations in water supply pressure, may be supplied with the alarm valve. If a retard chamber is supplied, only the listed chamber for a specific manufacturer and valve model shall be used. Alarm valves are FM Approved with specific trim, and no substitutes or omissions in part or in full are allowed. Alarms are tested by flowing water through the system test pipe. Pilot valves may be field-adjusted to assure alarm reliability. Unless otherwise noted in the listing, these valves have 175 psi (1205 kPa) rated working pressure. ...