Fire Sprinkler System

Overview

An automatic fire sprinkler system is a building-wide network of piping and heat-activated sprinklers that detects and controls a fire at its origin, discharging water only over the area that is actually burning. This is a wet-pipe system, meaning the piping is filled with pressurized water at all times so discharge begins the instant a sprinkler opens. Designed to NFPA 13, it combines a supervised water supply, an alarm-sensing riser, a fire pump set and distribution piping feeding sixty pendent heads.

Water enters through the Water Supply Assembly, which carries the backflow preventer and supervised OS&Y isolation valve. It passes the Alarm Check Valve Assembly, a clapper-type alarm check valve whose retard chamber, pressure switch and water motor gong signal flow. Demand flow and pressure are provided by the Fire Pump Set, a centrifugal fire pump with a jockey pump and listed controller. The Piping Network of cross mains and branch lines distributes water to each Sprinkler Head, a frame holding a heat-sensitive glass bulb over a sealed orifice. The Fire Department Connection lets the fire department augment supply, while the Fire Alarm Control Panel supervises the flow and tamper switches.

How it works

Each sprinkler holds a frangible glass bulb filled with a colored liquid that seals a cap against the orifice. Fire heat raises the air temperature at the ceiling; when the bulb reaches its rated temperature, typically 155 °F, the trapped liquid expands and shatters the glass, releasing the cap so water sprays off the deflector in a defined pattern. Only sprinklers over the fire open, limiting water damage. The pressure drop as water flows trips the alarm check valve, which ports water to the pressure switch and the hydraulically driven gong. The fire pump controller starts the main pump on the falling pressure to sustain the rated flow, while the jockey pump handles minor leakage so the main pump is not cycled needlessly. Tamper switches on the control valves report to the panel so a closed valve cannot silently disable the system.