The Venturi Valve is an air flow control device that varies the annular orifice to modulate the flow of air. The logarithmic profile of the valve body and the position of the internal damper assembly achieve the variable annular orifice. You can also refer to the orifice as a cone due to its shape. The cone is situated on an actuated shaft, which enables flow control through the full range of the valve, from 0% to 100%.
An increase in duct static pressure compresses a spring housed inside the cone and extends the spring when the pressure reduces. This spring moves the cone independently of the cone shaft, repositions it inside the valve body, and changes the annular orifice. This spring-activated cone travel enables instant mechanical flow adjustments independent of the actuator movement. The spring-enabled cone travel enables mechanical pressure independent flow control by the Venturi air valve.
The pressure-independent flow control feature of the Venturi Valves is functional between 0.3 in. W.C to 3.0 in. W.C for low pressure and 0.6 in. W.C to 3.0 in. W.C for medium pressure applications. This is due to weight, friction and other limiting factors, which attribute to the minimum force required for initiating cone travel.
If duct static pressure falls below the minimum level required, 0.3 in. W.C for low pressure and 0.6 in. W.C for medium pressure applications, there is not enough force to move the cone and it begins to compress the spring inside to activate cone travel.
If duct static pressure exceeds the maximum pressure limit allowed, 3.0 in. W.C, the cone fully compresses the spring inside and prevents further cone travel.
Due to the dynamic spring action in the cone assembly, the pressure drop is never constant across a Venturi Valve. Measure at the time of operation for a true reading. To ensure correct operation of the Venturi Valve, maintain the pressure drop across the valve between 0.3 in. W.C and 3 in. W.C for low pressure and between 0.6 in. W.C and 3 in. W.C for medium pressure applications.