Brady air volume control model AV42T, AV80T, AV100, AV120. An automatic air volume control maintains the correct volume of air in a atmospheric pressure tank and is essential to successful water system operation. Zinc die cast body , Buna N diaphragm and seal cap elastomers, brass spring and orifice; 100 PSI maximum pressure.

Unless the correct amount of air is maintained in the tank it will water log. Leakage of water at a faucet will then cause the system to start and stop frequently and needlessly.

The amount of air in a tank gradually diminishes, because of absorption of air in the water. If not replenished from time to time the tank becomes filled with water and the air under pressure becomes insufficient to force the water through the pipes. This is a water-logged tank condition.