In HVAC control systems, a bellows is used in which controllers?

In HVAC control systems, a bellows is used in which controllers?

• A. In both pressure and temperature controllers
• B. Only in pressure controllers
• C. Only with remote thermostats
• D. Only in temperature controllers

Answer: (A)

Bellows act as sensing elements that convert a physical stimulus into mechanical motion in pneumatic HVAC controls. In pressure controllers, the bellows respond to process pressure; when pressure changes, the bellows expand or contract and move a linkage that adjusts the controlled output to keep the pressure at the setpoint. In temperature controllers, a temperature-responsive bellows (often filled with a gas or fluid) expands or contracts as temperature changes, driving the linkage to regulate the actuator, damper, or valve to maintain the desired temperature. Because bellows can be designed to respond to either pressure changes or temperature-induced volume changes, they’re used in both types of controllers. The other options are too narrow since a bellows isn’t restricted to one kind of controller or to remote thermostats.

Bellows act as sensing elements that convert a physical stimulus into mechanical motion in pneumatic HVAC controls. In pressure controllers, the bellows respond to process pressure; when pressure changes, the bellows expand or contract and move a linkage that adjusts the controlled output to keep the pressure at the setpoint. In temperature controllers, a temperature-responsive bellows (often filled with a gas or fluid) expands or contracts as temperature changes, driving the linkage to regulate the actuator, damper, or valve to maintain the desired temperature. Because bellows can be designed to respond to either pressure changes or temperature-induced volume changes, they’re used in both types of controllers. The other options are too narrow since a bellows isn’t restricted to one kind of controller or to remote thermostats.