Red Seal Gasfitter — Class B Practice Exam

What is the function of a thermocouple in a gas system?

1. To detect the pilot light flame and maintain gas flow to the burner

2. To monitor gas pressure within the piping system

3. To convert gas to a usable liquid form

4. To regulate the temperature of the gas appliance

The correct answer is: To detect the pilot light flame and maintain gas flow to the burner

A thermocouple serves a critical safety function in a gas system by detecting the presence of a pilot light flame. It operates on the principle of thermoelectricity, generating a small voltage that varies with temperature. When the pilot light is lit, the thermocouple heats up and produces enough voltage to keep the gas valve open, allowing gas to flow to the burner. If the pilot light goes out, the temperature at the thermocouple drops, resulting in a stop of voltage generation. This action signals the gas valve to close, cutting off the gas supply and preventing potential gas leaks or explosions. This functionality is essential for ensuring safe operation, as it maintains the flow of gas only when the flame is present, thus reducing the risk of unburned gas accumulating in the environment. Other options, while relevant to gas systems, do not pertain directly to the thermocouple's specific role in flame detection and gas flow maintenance.