also fitted with a blower, which is a device that releases steam directly into the smokebox for use when a greater draught is needed without a greater volume of steam passing through the cylinders. An example of such situation is when the regulator is closed suddenly, or the train passes through a tunnel. If a single line tunnel is poorly ventilated, a locomotive entering at high speed can cause a rapid compression of the air within the tunnel. This compressed air may enter the chimney with substantial force. This can be extremely dangerous if the firebox door is open at the time. For this reason the blower is often turned on in these situations, to counteract the compression effect. 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 George Jackson 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-designed Mallard. Other designs include Giesl, Lemaître and Lempor blastpipes. References Locomotive parts Steam locomotive exhaust systems Steam locomotive technologies