The controller, also known as a constant air volume terminal (CAV box), is fitted horizontally and vertically in air conditioning systems’ supply and exhaust ducts to maintain a continuous air flow rate. Galvanized sheet serves as both the body and the control mechanism. The damper blade controls the air flow rate and is in the middle. To manually set the flow rate at a particular value, the airflow rate adjustment system features a rotating pointer, controlled flow range, and pointer lock.

There is no requirement for a power supply because the flow rate control is mechanical. A specific control mechanism in the manufacturing process of the blade and the flow rate adjustment system guarantees high control accuracy in the operating range of each size. Adjusting the lowest and maximum flow rates (Vmin, Vmax) will change how much air is needed. During pressure fluctuations, the flow rate of flowing air stays constant.