In order to provide a constant volume air system in a Variable Air Volume system for some part of the floors such as operation rooms in hospital or laboratory, a special terminal box needs to be installed for those areas. This type of the terminal box is called the Venturi valve. An airflow control device in Venturi valve continuously measuring the velocity pressure and then reacting by commanding the actuator to a new position to maintain flow.
The Venturi valve adjusts and compensates for fluctuations of duct pressure by using a mechanical pressure-independent cone and spring assembly that moves in and out of the Venturi orifice, increasing and decreasing the airflow in a very predictable manner when exposed to pressure drops within a specified range. It’s this pressure independent cone assembly that dictates what minimum static pressures are required to operate properly.
The pressure range for using a medium pressure Venturi valves, the static pressure requirements are from .6” W.C. on the low end, to 3.0” W.C. on the high. While in that range the valve will provide consistent, accurate turndowns of 20-1 with ±5% accuracy of the commanded value. A low pressure Venturi valve can operate from .3” W.C. to 3.0” W.C.
