Later Development
Little development of the basic principles of smokebox design took place until 1908, when the first comprehensive examination of steam-raising performance was carried out by W.F.M. Goss of Purdue University. These principles were adopted on the Great Western Railway by Churchward. A later development was the so-called jumper-top blastpipe which controlled the area of the blastpipe at different steaming rates to maximise efficiency.
The aim of blastpipe modification is to obtain maximum smokebox vacuum with minimum back pressure on the pistons. The simplest modification is a double chimney with twin blastpipes, but many other arrangements have been tried. Towards the end of the steam era the Kylchap exhaust was popular and used on the Nigel Gresley's Mallard. Other designs include Giesl, Lemaître and Lempor blastpipes.
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