Alarm check valves serve two purposes:

1. To check water pressure into the sprinkler system.
2. Provide a water flow alarm, either electrically or mechanically an Alarm Check valve has valve trim that is required to provide alarms.
   It can either be vertical or horizontal.
   (Vertical trim is shown) Valve trim is small piping attached to valves to provide a specific function such as cause alarm or automatically drain ports.

         Retard Chambers

Retard Chambers are empty tanks that provide a mechanical delay for water flow alarm.

Where water pressures are variable, such as a city water supply, the retard chamber accepts short water surges without causing an alarm.
In an extended water surge, the retard chamber will fill and cause an alarm.