G2 Gas Fitter Practice Exam

Which of the following flame detectors generates sufficient electricity to operate a main gas valve and an operating/limit control circuit?

1. Thermocouple

2. Thermopile

3. Photocell

4. Ionization

The correct answer is: Thermopile

The thermopile is designed to generate sufficient electricity to operate a main gas valve and an operating/limit control circuit, making it the correct choice in this scenario. This device consists of multiple thermocouples connected in series or parallel, allowing it to produce a higher voltage output compared to a single thermocouple. This combination of thermocouples harnesses the temperature differences within a gas flame to generate the necessary electrical energy to power various components within a heating system, such as the gas valve and limit controls. In contrast, a thermocouple generates a relatively small voltage when exposed to temperature differences, generally suitable for small applications like pilot lights, but insufficient to operate heavy-duty functions such as a gas valve. A photocell relies on the presence of light and converts light energy into electrical energy, which is not applicable in flame detection for gas systems. The ionization detector operates based on the electrical conductivity of the ionized gas in a flame but does not generate the same level of electrical power required for operating main gas valves. Thus, the thermopile stands out as the most viable option for powering the necessary control elements in gas fitting applications.