What type of control device uses compressed air to send variable signals from a thermostat and controller?

Pneumatic control devices use compressed air to transmit signals for regulating HVAC systems and other controls. In these systems, the thermostat detects temperature changes and sends a corresponding amount of compressed air to the controller or actuator. This air pressure variation allows for precise adjustments in the system, enabling it to respond effectively to the thermal environment.

Pneumatic controls are often valued for their simplicity, reliability, and effectiveness in older systems. They operate through a network of tubes and valves, working similarly to an electrical circuit but using air pressure instead of electrical signals. This characteristic distinguishes pneumatic control from electric, mechanical, and hydraulic options, as those methods rely on electrical currents, physical movements, or fluid dynamics, respectively, rather than air pressure to communicate and execute control functions.