One was a burner control designed to detect if the flame in the firebox went out while the boiler was operating.
There was also, from late 1943, a longer version with ten-coupled wheels and a wide firebox ; they were in fact much better but only 150 were built.
Lighting the load from the top of the pile yields a candle-like burn, allowing the firebox to heat up as the volatile gases are being more evenly released.
The combustion chamber was an extension of the inner firebox into the boiler barrel, to give extra heating surface where the heat is the greatest.
As the warm air rises, cooler air from the room flows into the firebox , fanning the fire, creating more heat in an ongoing cycle.
As we continued up the hill, the sound of air being sucked into the firebox was deafening, even with ear plugs.
You can remove the firebox covers and check inside the firebox for rust and scale deposits.
Four of them could be seen on each side of the firebox , running parallel with the fire bed a couple of feet or so above it.
The firebox was of the well-known Belpaire type whilst the boiler would be of the maximum British dimensions.
Johanns, an engine driver, Reginald recalled, was severely injured when the firebox of the locomotive blew back.