Сифон и поддувало

Интенсивность горения топлива, а, как следствие, и температура топки, регулируются подачей воздуха в топку. Кислород воздуха усиливает огонь.

The primary way to feed air to the firebox is by opening the regulator and propelling the vehicle. As the steam is expelled from the boiler through steam chest and cylinders out into the atmosphere, fresh air is drawn to the firebox. This happens with every gear cycle, and the higher the cutoff setting the more the airflow.

Вдобавок, есть ещё два элемента управления, предназначенные для регулирования тяги: сифон и поддувало.

Blower is usually operated by a valve. When open, it releases steam from the boiler around the chimney area. This creates vacuum, pulling in air into the firebox. This is used when a vehicle is stationary. Having the blower open while accelerating is wasteful however, because the acceleration airflow is vastly superior to blower.

Damper is usually operated by a lever. When closed (pushed down) it chokes the airflow, drastically reducing fire temperature. This is used to intentionally cut steam production when it is no longer needed.