Wet Alarm Valve Operation

A wet alarm valve, core of wet-pipe sprinkler systems, stays closed under normal conditions. System water fills both its inlet (connected to the water supply) and outlet (linked to sprinkler pipes). Water pressure presses a clapper valve tightly against its seat, sealing the flow path. This balance keeps the valve shut, maintaining stable pressure in the sprinkler system and preventing unintended water release.

When a fire occurs, heat activates sprinklers (e.g., glass bulb bursts). Water flows out of the activated sprinklers, quickly lowering pressure on the valve's outlet side. The inlet side, still connected to the water supply, retains higher pressure. This sudden pressure difference disrupts the clapper's balance, creating a force that pushes the clapper away from its seat.

Once the clapper opens, water from the inlet rushes through the valve to the sprinkler pipes, sustaining water supply for fire suppression. Simultaneously, a small portion of water diverts into the alarm line attached to the valve. This water flow triggers devices like a water motor gong (audible alarm) or pressure switch (signal to fire panels), alerting people to the fire.

The wet alarm valve remains open until the fire is extinguished and the system is manually reset. First, the water supply is shut off, and the sprinkler system is drained. Then, the clapper is repositioned to its seat. Restoring water supply repressurizes both sides of the valve, rebalancing pressure to hold the clapper closed-returning the system to its normal, ready state.