A bellows is used

A bellows is used

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

Answer: (C)

Bellows act as sensitive sensing elements that translate pressure changes into mechanical motion. In a pressure controller, the process pressure pushes on the bellows, causing it to expand or contract and move the control linkage to keep the desired pressure. In a temperature controller using a remote sensing bulb, changes in temperature alter the pressure in the sensing line, which then moves the bellows just as a direct pressure would, driving the control action. Because a bellows can respond to both direct pressure and the pressure generated by a temperature-sensing system, it fits in both types of controllers, making it a versatile sensing element.

Bellows act as sensitive sensing elements that translate pressure changes into mechanical motion. In a pressure controller, the process pressure pushes on the bellows, causing it to expand or contract and move the control linkage to keep the desired pressure. In a temperature controller using a remote sensing bulb, changes in temperature alter the pressure in the sensing line, which then moves the bellows just as a direct pressure would, driving the control action. Because a bellows can respond to both direct pressure and the pressure generated by a temperature-sensing system, it fits in both types of controllers, making it a versatile sensing element.