Barrel
The barrel, a hollow metal shaft, is the part of the burner twisted onto the base. At the bottom part of the barrel are inlet holes, which allow oxygen to enter. The barrel is built to turn on a threaded mount to allow air partially into or cut it off from entering the air inlet holes. Turning the barrel collar, which consequently moves it up or down, regulates the air. Screwing the barrel down into the base blocks the air inlets; turning the barrel in reverse permits more air to pass through.
Air Vents
The air vents, the air inlet holes located at the base of the barrel, become smaller as the barrel is screwed down, limiting air entry into the barrel and providing richer gas concentration in proportion to air. High gas concentration produces a hot, blue flame, which rises above the barrel and burns noisily with the introduction of too much gas. Allowing greater air concentration by screwing the barrel upward will produce a weak, sooty, yellow flame.
Gas Inlet
Gas enters the barrel through a rubber tube connected to the gas line at the center of the base. The gas flows through the gas inlet and through the base via a small hole at the barrel, and is directed upward to eventually mix with oxygen and produce a flame.
Needle Valve
The needle valve regulates the gas flow that enters the barrel. A small hole on the needle valve, called a "spud," allows gas entry. By turning the threaded thumb wheel built into the needle valve, a technician can control the amount of gas that enters the barrel. This particular part makes the tirril Bunsen burner different from a regular Bunsen burner.