Model P Alarm check valves 4″/ 6″ are designed for use in wet pipe system and may be installed in the vertical or horizontal position with the appropriate trim package. Model P Alarm Check Valve is a hydraulically operated external resetting differential latching style valve designed for use where quick-opening and total flooding of sprinkler system piping is desired. It is used as an automatic water control valve in Deluge, Dry Pipe, or Precaution systems, as well as Foam-water sprinkler systems. UL certified.