21. The third area forwards contained superheater headers, the regulators and the smokebox, but no deliberate heating surface . 22. These locomotives differed from those of the previous order by having slightly larger boilers with an increased heating surface . 23. In the smokebox, which is long, was located a small tube superheater with a heating surface of. 24. She had six water-tube boilers with a combined heating surface of that supplied steam at 400 screw propellers. 25. "Clan Campbell " s boilers had a combined heating surface of and supplied steam at 220 NHP. 26. The ship was also re-boilered with two water tube boilers that had a heating surface of and operated at. 27. This had the additional advantage of wrapping the heating surface closely around the furnace, but that was a secondary benefit. 28. Brick-lined end walls to this casing housed the firedoors or oil burner quarls, but had no heating surface . 29. The three most important improvements were :-wide steam passages, large heating surfaces and generous bearing surfaces on the wheels. 30. In the case of " Bonnington " the grate area of the boiler was over and the heating surface was.
