Gas Fitter Practice Test

What purpose does a thermocouple serve in a gas appliance?

1. A. To ignite the pilot light

2. B. To detect changes in temperature

3. C. To ensure safe operation by shutting off gas supply

4. D. To measure gas pressure

The correct answer is: C. To ensure safe operation by shutting off gas supply

A thermocouple primarily serves the purpose of ensuring safe operation by shutting off the gas supply. It functions as a safety device that monitors the temperature of the pilot light or burner. When the pilot light is lit, the thermocouple generates a small voltage as a result of the heat from the flame. This voltage keeps an electromagnetic valve open, allowing gas to flow to the burner. If the pilot light goes out, the temperature drops, causing the voltage to decrease. This leads to the closure of the valve, effectively stopping the flow of gas and preventing a dangerous buildup of gas in the appliance. While the other options touch on related concepts, they do not accurately describe the primary function of a thermocouple. Igniting the pilot light is typically performed by a piezoelectric igniter or a spark generator, not a thermocouple. Although thermocouples can detect changes in temperature, their primary role in gas appliances is related to safety and gas supply management. Lastly, measuring gas pressure is a different function typically handled by a pressure gauge or regulator. Thus, the correct function of a thermocouple in a gas appliance is indeed to ensure safe operation by shutting off the gas supply when needed.