Vertical cross-tube boiler

Applications such as cranes only require steam intermittently, allowing the boiler to recover pressure between lifts.

The boiler consists of a cylindrical vertical external shell, with a large firebox inside this, filling perhaps half of the total height.

The main evaporative surface is provided by a pair of large water-filled cross-tubes across this firebox and directly exposed to the radiant heat of the fire.

In practice, the boilers were robustly constructed and operating at fairly low pressure, and so minor wastage was acceptable.

The most likely location for wastage developing was around the uptake flue, at the operating water level where activity and erosion was most severe.

Vertical cross-tube boiler,
A sectioned view of a cross-tube boiler. The section shows a single vertical flue or fire-tube, with two large water-tubes across the firebox beneath this.
A railway-mounted steam crane, with a vertical boiler mounted at the rear of the crane platform.
Steam crane, with cross-tube boiler