The blastpipe is part of the

exhaust system An exhaust system is used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes. Depending on the overall system ...

of a

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

that discharges exhaust steam from the

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infin ...

s into the

smokebox A smokebox is one of the major basic parts of a steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler. The smoke then enters the smokebox, and is e ...

beneath the

chimney A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typic ...

in order to increase the draught through the fire.

History

The primacy of discovery of the effect of directing the exhaust steam up the chimney as a means of providing draft through the fire is the matter of some controversy, Ahrons (1927) devoting significant attention to this matter. The exhaust from the cylinders on the first steam locomotive – built by

Richard Trevithick Richard Trevithick (13 April 1771 – 22 April 1833) was a British inventor and mining engineer. The son of a mining captain, and born in the mining heartland of Cornwall, Trevithick was immersed in mining and engineering from an early age. He w ...

– was directed up the chimney, and he noted its effect on increasing the draft through the fire at the time. At Wylam,

Timothy Hackworth Timothy Hackworth (22 December 1786 – 7 July 1850) was an English steam locomotive engineer who lived in Shildon, County Durham, England and was the first locomotive superintendent of the Stockton and Darlington Railway. Youth and early work ...

also employed a blastpipe on his earliest locomotives, but it is not clear whether this was an independent discovery or a copy of Trevithick's design. Shortly after Hackworth,

George Stephenson George Stephenson (9 June 1781 – 12 August 1848) was a British civil engineer and mechanical engineer. Renowned as the "Father of Railways", Stephenson was considered by the Victorians a great example of diligent application and thirst for ...

also employed the same method, and again it is not clear whether that was an independent discovery or a copy of one of the other engineers.

Goldsworthy Gurney Sir Goldsworthy Gurney (14 February 1793 – 28 February 1875) was an English surgeon, chemist, architect, builder, lecturer and consultant. He was a prototypical British gentleman scientist and inventor of the Victorian era. Amongst many acc ...

was another early exponent, whose claim to primacy was energetically advocated by his daughter Anna Jane.''Bude's Forgotten Genius – Sir Goldsworthy Gurney''. B. Dudley-Stamp, 1993. Bude-Stratton Town CouncilThe Life of Edward White Benson
1899, p.455 The locomotives at the time employed either a single flue boiler or a single return flue, with the fire grate at one end of the flue. Because a single flue had to be wide to let the exhaust through, a blastpipe could lift the fire, pulling soot and sparks up the chimney. It was not until the development of the multitubular boiler that a forced draft could be used safely and effectively. The combination of multi-tube boiler and steam blast are often cited as the principal reasons for the high performance of ''Stephenson's Rocket, Rocket'' of 1829 at the Rainhill Trials.

Description

Soon after the power of the steam blast was discovered it became apparent that a

was needed beneath the chimney, to provide a space in which the exhaust gases emerging from the boiler tubes can mix with the steam. This had the added advantage of allowing access to collect the ash drawn through the fire tubes by the draught. The blastpipe, from which steam is emitted, was mounted directly beneath the chimney at the bottom of the smokebox. The steam blast is largely self-regulating: an increase in the rate of steam consumption by the cylinders increases the blast, which increases the draught and hence the temperature of the fire. Modern locomotives are 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 LNER Class A4 4468 Mallard, Mallard. Other designs include Giesl ejector, Giesl, Jean Lemaître, Lemaître and Lempor ejector, Lempor blastpipes.

References

* * * {{Steam locomotive exhaust systems Locomotive parts Steam locomotive exhaust systems Steam locomotive technologies