Which type of switch is used on the alarm line of an alarm valve that has a retard chamber in the trim?

• A. Flow switch
• B. Temperature switch
• C. Proximity switch
• D. Pressure switch

Answer: (D)

Pressure switch is used because the alarm line in an alarm valve with a retard chamber is monitored for changes in hydraulic pressure to trigger the fire alarm. The retard chamber slows pressure changes to avoid false alarms, but the sensing element still needs to respond to pressure, not flow, heat, or proximity. Flow switches detect actual water movement, which isn’t the signal the alarm line uses here; temperature switches respond to heat, and proximity switches detect metal presence. The alarm signal on this trim is generated by a pressure switch reacting to the pressure change in the alarm line.