A vertical pipe positioned directly beneath the chimney in the smokebox of a steam locomotive. It takes exhaust steam from the cylinders and jets it upward, creating a partial vacuum that pulls hot gases through the boiler tubes and draws fresh air into the firebox. The size and shape of the nozzle dictate the draft intensity and the back pressure on the cylinders.
Heard on the job
The engine wouldn't steam properly until the shop adjusted the blastpipe alignment.
Insider tip
The rhythmic chuffing sound of a steam locomotive is actually the exhaust steam exiting the blastpipe.