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The 'blastpipe' is part of a steam locomotive that discharges exhaust steam from the cylinders into the smokebox beneath the chimney in order to increase the draught of the fire.
The primacy of discovery of the effect of directing the exhaust steam up the chimney as a means of providing draft on 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, bult by Richard Trevithick was directed up the chimney, and he noted its effect on increasing the draft on the fire at the time. At Wylam, Timothy Hackworth also employed a blastpipe on his earliest locomotives, but it is not clear whether this was an independent rediscovery or a copy of Trevithick's design. Shortly after Hackworth, George Stephenson also employed the same method, and again it is not clear whether that was an independent discovery or a copy of one or other of the other two 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 strong 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 possitioned, 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'' of 1829 at the Rainhill Trials.
Soon after the power of the steam blast was discovered, it became apparent that a smokebox 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 blast pipe, from which steam is admitted, 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 steam blast, which increases the draught and thence 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 such situation is when the regulator is closed suddenly, or the train passes through a tunnel.
Little development of the basic principles of smokebox design 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.
★ How Steam Locomotives Really Work, P.W.B. Semmens and A.J. Goldfinch, , , OUP, 2003, ISBN 0-19-860782-2
★ George and Robert Stephenson: The Railway Revolution, L.T.C. Rolt, , , Pelican, 1978, ISBN 0-14-022063-1
★ The British Steam Railway Locomotive 1825-1925, E.L. Ahrons, , , , 1927,
| Contents |
| History |
| Description |
| Later development |
| References |
History
The primacy of discovery of the effect of directing the exhaust steam up the chimney as a means of providing draft on 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, bult by Richard Trevithick was directed up the chimney, and he noted its effect on increasing the draft on the fire at the time. At Wylam, Timothy Hackworth also employed a blastpipe on his earliest locomotives, but it is not clear whether this was an independent rediscovery or a copy of Trevithick's design. Shortly after Hackworth, George Stephenson also employed the same method, and again it is not clear whether that was an independent discovery or a copy of one or other of the other two 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 strong 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 possitioned, 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'' of 1829 at the Rainhill Trials.
Description
Soon after the power of the steam blast was discovered, it became apparent that a smokebox 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 blast pipe, from which steam is admitted, 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 steam blast, which increases the draught and thence 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 such situation is when the regulator is closed suddenly, or the train passes through a tunnel.
Later development
Little development of the basic principles of smokebox design 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.
References
★ How Steam Locomotives Really Work, P.W.B. Semmens and A.J. Goldfinch, , , OUP, 2003, ISBN 0-19-860782-2
★ George and Robert Stephenson: The Railway Revolution, L.T.C. Rolt, , , Pelican, 1978, ISBN 0-14-022063-1
★ The British Steam Railway Locomotive 1825-1925, E.L. Ahrons, , , , 1927,
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