Transverse boiler

When descending steep hills, there is less risk of the firebox crown being exposed above the water level and dangerously overheating.

The boiler consists of one long horizontal transverse drum, with a central locomotive-style firebox mounted in an extension beneath.

Fire-tubes lead to a shallow smokebox at each side, from which return tubes pass to a central chamber beneath the chimney.

An unusual feature is that rather than the usual single blastpipe beneath the chimney, there are 14 of them on each side inside each smokebox, pointing into the return tubes.

[1] Exhaust steam from the engine reaches these blastpipes through a prominent copper pipe on the outside of each smokebox door.