The alarm valve is an alarm device designed for installation in a sprinkler system. It is used to actuate a fire alarm when flow of water from the sprinkler system exceeds that of a single sprinkler. When a sprinkler is in operation, the resulting water flow lowers the pressure in the sprinkler system. The greater water supply pressure then causes the alarm valve clapper to open. The seat ring opening of the alarm valve allows the water to flow into the alarm line connection which will then operate the alarm gong.

The by-pass connection in the check valve allows pressure surges from the supply to by-pass the alarm valve clapper. An excess system pressure is thus created which steadies the clapper.

A Retard Chamber is used when the water supply pressure fluctuates, such as public main water supply. It is used to prevent false alarms caused by surges or fluctuations in pressure.