Humidifier control must provide immediate response and precise modulation to maintain the required humidity accurately. Faulty control can lead to overloading the ducts with moisture and the creation of wet spots or failure to provide the required humidity level.

Two design factors affect the accuracy of humidifier control—the control (metering) valve and the actuator or operator that positions the valve.

Precise flow control can be achieved with a valve designed expressly for the purpose of adding steam to air. All Armstrong Series 9000 and Series 1000 modulating humidifiers use uniquely modified parabolic plug-type valves to accomplish this task. The modification of true linear characteristics provides more precise control when capacity requirements are very low and the valve is cracked just off the seat.