Pneumatic thermostats are designed to control the air handling system through the use of an air-filled control tube that is capable of sending signals. Understanding how a pneumatic thermostat operate is the first step to getting the most out of one of these types of devices.
How a Pneumatic Thermostat Works
A pneumatic thermostat ultilizes a bi-metallic strip that is capable of responding to changes that occur in the temperature. In response, the pneumatic thermostat increases or decreases the pressure of the air within the control tube.
Separate components within the air handling system are capable of responding to these pressure changes within the control tube, and through the ductwork they are able to activate either heating or cooling to occur accordingly.
Direct and Reverse
The direct acting pneumatic thermostat, or DA, is responsible for increasing the pressure in the branch line as temperature is increased. On the other hand, the reverse acting pneumatic thermostat, or RA, is responsible for decreasing the pressure in the branch line as temperature is increased.
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