Which of the following statements about atmospheric burners is TRUE?

The statement that air and gas ignite in the mixing tube is true regarding atmospheric burners. Atmospheric burners operate by mixing gas with air to achieve the necessary combustion conditions. The mixing tube is designed to allow a specific air-to-gas ratio, promoting efficient combustion. When the mixture flows through the burner, it ignites at various points, but the initial ignition often occurs in the mixing tube where the gases are combined effectively. This is a defining characteristic of how atmospheric burners function, relying on natural draft and the design of the burner to ensure proper combustion.

In contrast, the other statements do not accurately represent the nature of atmospheric burners. These burners do not ignite exclusively at the burner ports; instead, the ignition can occur throughout the mixing area. They also do not require constant manual ignition, as many are designed for automatic ignition with safety features, and they do not typically have a special ignition switch, relying instead on basic designs that engage the ignition process without the need for special controls. Understanding these features helps clarify the operation and efficiency of atmospheric burners in fuel gas systems.