5th Class Power Engineering Practice Exam

The sensing element of a remote bulb thermostat operates by utilizing a bulb, capillary tube, and a bellows combination that contains a volatile liquid. This setup is designed to respond to temperature changes in the environment.

When the temperature rises, the liquid inside the bulb expands and travels through the capillary tube, resulting in increased pressure on the bellows. This mechanical movement of the bellows can then activate a switch that controls the heating or cooling system, thus maintaining the desired temperature.

This combination of components is essential for the functionality of a remote bulb thermostat, as it allows for accurate temperature sensing and provides a reliable response mechanism to changes in temperature.

Other options lack the complexity and functionality associated with temperature regulation in HVAC systems. For instance, while a capillary tube and gas might be part of some thermodynamic systems, they do not provide the necessary response mechanism for a remote thermostat. Similarly, electronic diodes and resistors, as well as thermal sensors and wires, represent electronic control systems rather than the traditional mechanical systems used in remote bulb thermostats.