Steam generator (boiler)

[1] The narrow-tube construction, without any large-diameter drums or tanks, means that they are safe from the effects of explosion,[note 1] even if worked at high pressures.

The first helices (in the flow direction) are small-diameter tubes, wrapped in large diameter turns.

Succeeding turns are coiled inside this and the tube is of progressively increasing diameter, to allow for a constant flow rate as the water evaporates into steam and forms bubbles.

The exhaust gases turn upwards and flow over the outside of the bell, usually passing additional helices that are used as an initial feedwater heater.

The Clayton steam generator is similar to the Stone-Vapor, but the burner and flow directions are reversed.