(Build; Fire Pr) A grid system of water pipes and spaced discharge heads installed in a building to control and extinguish fires. Note: There are four basic types of sprinkler systems: Wet, dry, deluge, and preaction. Wet pipe: All piping is filled with pressurized water, which is released when a fusible link melts in a sprinkler head. Dry pipe: All piping contains pressurized air. When a sprinkler opens, air pressure is released, and the dry pipe valve opens to admit water into the system and to any open. sprinkler head. Deluge: All sprinkler heads are open and water is held back at the main (deluge) valve. When this valve is actuated, water is delivered to all heads simultaneously. Preaction: The main water control valve is opened by an actuating device which permits water to flow to individual sprinkler heads. Sprinkler systems include a suitable water supply, such as a gravity tank, fire pump, reservoir, pressure tank, or connections to city mains. In addition there is us: a controlling valve and devices for signalling alarms when the system is actuated