Blastpipe
Encyclopedia
The blastpipe is part of the exhaust system
Steam locomotive exhaust system
The Steam locomotive exhaust system consists of those parts of a steam locomotive which together discharge exhaust steam from the cylinders in order to increase the draught through the fire...

 of a steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

 that discharges exhaust steam from the cylinder
Cylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

s into the smokebox
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 exhausted to the atmosphere through the chimney .To assist...

 beneath the chimney
Chimney (locomotive)
The chimney of a steam locomotive is a part of the exhaust system which helps in the creation of draught through the boiler and carries the exhaust steam and smoke clear of the driver's line of sight...

 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
Richard Trevithick was a British inventor and mining engineer from Cornwall. His most significant success was the high pressure steam engine and he also built the first full-scale working railway steam locomotive...

 – 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
Timothy Hackworth was a 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
George Stephenson was an English civil engineer and mechanical engineer who built the first public railway line in the world to use steam locomotives...

 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.

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. For boilers of this design the blast of a contracted orifice blastpipe was too strong, and would lift the fire. It was not until the development of the multitubular boiler that the centrally positioned, contracted orifice blastpipe became standard. The combination of multi-tube boiler and steam blast are often cited as the principal reasons for the high performance of Rocket
Stephenson's Rocket
Stephenson's Rocket was an early steam locomotive of 0-2-2 wheel arrangement, built in Newcastle Upon Tyne at the Forth Street Works of Robert Stephenson and Company in 1829.- Design innovations :...

of 1829 at the Rainhill Trials
Rainhill Trials
The Rainhill Trials were an important competition in the early days of steam locomotive railways, run in October 1829 in Rainhill, Lancashire for the nearly completed Liverpool and Manchester Railway....

.

Description

Soon after the power of the steam blast was discovered it became apparent that a smokebox
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 exhausted to the atmosphere through the chimney .To assist...

 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
Purdue University
Purdue University, located in West Lafayette, Indiana, U.S., is the flagship university of the six-campus Purdue University system. Purdue was founded on May 6, 1869, as a land-grant university when the Indiana General Assembly, taking advantage of the Morrill Act, accepted a donation of land and...

. These principles were adopted on the Great Western Railway
Great Western Railway
The Great Western Railway was a British railway company that linked London with the south-west and west of England and most of Wales. It was founded in 1833, received its enabling Act of Parliament in 1835 and ran its first trains in 1838...

 by Churchward
George Jackson Churchward
George Jackson Churchward CBE was Chief Mechanical Engineer of the Great Western Railway in the United Kingdom from 1902 to 1922.-Early career:...

. 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
Back pressure
Back pressure refers to the resistance to a moving fluid by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents, against its direction of flow....

 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
Kylchap
The Kylchap steam locomotive steam locomotive exhaust system was designed and patented by the famous French steam engineer André Chapelon, using a second-stage nozzle designed by the Finnish engineer Kyösti Kylälä and known as the Kylälä spreader; thus the name KylChap for this design.The Kylchap...

 exhaust was popular and used on the Nigel Gresley
Nigel Gresley
Sir Herbert Nigel Gresley was one of Britain's most famous steam locomotive engineers, who rose to become Chief Mechanical Engineer of the London and North Eastern Railway . He was the designer of some of the most famous steam locomotives in Britain, including the LNER Class A1 and LNER Class A4...

's Mallard
LNER Class A4 4468 Mallard
Number 4468 Mallard is a London and North Eastern Railway Class A4 4-6-2 Pacific steam locomotive built at Doncaster, England in 1938. While in other respects a relatively typical member of its class, it is historically significant for being the holder of the official world speed record for steam...

. Other designs include Giesl
Giesl ejector
A Giesl ejector is a suction draught system for steam locomotives that works on the same principle as a feedwater pump.This ejector was invented in 1951 by the Austrian engineer, Dr. Adolph Giesl-Gieslingen. The Giesl ejector ensures improved suction draught and a correspondingly better use of...

, Lemaître
Jean Lemaître
Jean Lemaître was a mechanical engineer from the Nord Belge Railway, who developed a Steam locomotive exhaust system.The Lemaître Exhaust featured 5 nozzles in a circular pattern exhausting up a large-diameter stack, with a variable area nozzle exhausting up the center, and improved efficiency by...

 and Lempor
Lempor ejector
The Lempor ejector is a Steam locomotive exhaust system developed by noted Argentine locomotive engineer Livio Dante Porta. In a steam locomotive, draft is produced in the firebox by exhausting the steam coming from the cylinders out of the chimney, or also by a blower. The LemPor exhaust delivers...

blastpipes.
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