When a flame is established, the hot gas passes over what type of spring?

The correct answer is bimetal. In many heating systems, particularly those involving gas appliances, a bimetallic spring is utilized for its ability to respond to varying temperatures. Bimetallic springs are composed of two different metals that expand at different rates when heated. This property allows the spring to bend and move in response to temperature changes, effectively serving as a temperature sensing and control mechanism.

When a flame is established in a gas appliance, the heat generated causes the bimetallic spring to react, helping to control safety devices such as gas valves. Because it is directly affected by the temperature of the hot gases, the bimetallic spring can ensure that the gas flow is regulated appropriately, preventing potential hazards such as overheating or gas leaks.

Other types of springs like coil, compression, and tension springs are used in various applications but do not offer the same temperature-sensitive characteristics that are crucial in gas appliance operations. Coil springs, for example, are typically used to store energy or maintain tension. Compression springs resist compression forces while tension springs resist stretching forces. For applications specifically involving the response to heat and temperature, bimetallic springs are preferred due to their quick and responsive nature.