Shell boiler
Encyclopedia
A shell or flued boiler is an early, and relatively simple, form of boiler
used to make steam
, usually for the purpose of driving a steam engine
. The design marked a transitional stage in boiler development, between the early haystack boilers and the later multi-tube fire-tube boiler
s. A flued boiler is characterized by a large cylindrical boiler shell forming a tank of water, traversed by one or more large flue
s containing the furnace
. These boilers appeared around the start of the 19th century and some forms remain in service today. Although mostly used for static steam plants, some were used in early steam vehicles, railway locomotives and ships.
Flued boilers were developed in an attempt to raise steam pressures and improve engine efficiency. Early haystack designs of Watt
's day were mechanically weak and often presented an unsupported flat surface to the fire. Boiler explosion
s, usually beginning with failure of this firebox plate, were common. It was known that an arched structure was stronger than a flat plate and so a large circular flue tube was placed inside the boiler shell. The fire itself was on an iron grating placed across this flue, with a shallow ashpan beneath to collect the non-combustible residue. This had the additional advantage of wrapping the heating surface closely around the furnace, but that was a secondary benefit.
Although considered as low-pressure (perhaps 25 psi (1.7 atm)) today, this was regarded as high pressure compared to its predecessors. This increase in pressure was a major factor in making locomotives (i.e. small self-moving vehicles) such as Trevithick's
into a practical proposition.
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The simplest boiler for locomotives had a single straight flue. It was widely used by many of the early locomotive makers, including Blenkinsop
's locomotives for the Middleton railway
and Stephenson's Locomotion
.
This type of boiler is simple to manufacture and strong enough to support "high pressure" (for the period) steam with expansive working in the cylinders. There is also good gas flow through the large flue, so that the fire receives sufficient draught from the action of a tall chimney
alone. However it also has little heating area, so is inefficient and burns a large amount of coal.
A simple flue must be long if it is to offer adequate heating area. In a short boiler shell, such as required for a steam locomotive
, this may be done by using a U-shaped return flue that bends back on itself.
Richard Trevithick had already used a return flue with his first 1802 Pen-y-darren engine and 1803 Coalbrookdale
locomotive design. These boilers were heavily built of cast iron
, short and flat-ended. His 1805 "Newcastle
" locomotive (actually built in Gateshead
) began to show one characteristic feature of the return-flued boiler, a prominent dome shape to resist steam pressure in the solid end opposite both furnace and chimney. In this case, the boilermaking, now of wrought iron
plates, must have been complicated by Trevithick's single long-travel horizontal cylinder (9 inch diameter × 36 inch stroke) which emerged through this domed end. This did make work easier for the fireman though, as he was no longer trying to reach a firedoor beneath the long crosshead of the piston.
William Hedley
used this pattern of boiler for his 1813 locomotives Puffing Billy
and Wylam Dilly
. Through the Wylam
colliery and its owner Christopher Blackett
, Hedley would have been familiar with Trevithick's engine.
Timothy Hackworth
's 0-6-0 Royal George of 1827 also used a return-flued boiler, although it is best known for its pioneering use of a deliberate blastpipe
to encourage draught on the fire. His lighter weight 0-4-0 version for the Rainhill Trials
, Sans Pareil
was very similar. Even though they appeared antiquated as soon as the Trials were over, the Canadian Samson
of this pattern was built in 1838 and still in service in 1883.
Co. of Marion, Ohio
for their "New Huber" traction engine
s, from 1885 to 1903.
These were not, however, return-flue boilers in the sense used here, but rather return-tube boilers. They had a single large cylindrical furnace tube, a combustion chamber external to the boiler's pressure shell, then multiple, narrow fire-tubes returning to a horseshoe-shaped smokebox
above and around the firedoor. The proximity of this smokebox to the fireman led to their nickname of "belly burners". Their design thus has more in common with the horizontal launch-type boiler
s (as used by Sir Arthur Heywood
) or the Scotch marine boiler
than they do with the simple single-flue boiler.
By this time, the locomotive boiler had become ubiquitous for traction engines. Compared to this, the advantage of the Huber boiler was that the firetubes could be replaced more easily, without needing to work from within an enclosed firebox.
's "high-pressure" Cornish boiler, first installed at Dolcoath mine
in 1812. This is a long horizontal cylinder with a single large flue containing the fire. As the furnace relied on natural draught, a tall chimney
was required at the far end of the flue to encourage a good supply of air (oxygen) to the fire.
For efficiency, Trevithick's innovation was to encase beneath the boiler with a brick
-built chamber. Exhaust gases passed through the central flue and then routed outside and around the iron boiler shell. To keep the chimney clear of the firing space, the brick flue passed first underneath the centre of the boiler to the front face, then back again along the sides and to the chimney.
Cornish boilers had several advantages over the preceding wagon boilers: they were composed of mostly curved surfaces, better to resist the pressure. Their flat ends were smaller than the flat sides of the wagon boiler and were stayed by the central furnace flue, and sometimes by additional long rod stays. A less obvious advantage was that of boiler scale. Wagon or haystack boilers were heated from beneath and any scale or impurities that formed a sediment settled upon this plate, insulating it from the water. This reduced heating efficiency and could in extremis lead to local overheating and failure of the boiler plates. In the flued boiler, any sediment fell past the furnace flue and settled out at the bottom of the boiler shell, where it had less effect.
In model engineering
, the Cornish boiler, particularly when fitted with Galloway tubes (see Lancashire Boiler, below), is an excellent choice for gas-fired boilers and model steam boats. It is simple to build and as efficient as any small-scale boiler.
, where the hard Northern coal was of less calorific value than the Welsh coal used in the South West and required a larger fire. Alternatively it may be considered as a shortened Cornish boiler with a waggon boiler placed in front of it with a larger fire beneath that. It suffers the same drawback as the wagon boiler: the concave firebox plate is mechanically weak and this either limits the working pressure or requires extra mechanical staying.
The Lancashire boiler is similar to the Cornish, but has two large flues containing the fires instead of one. It is generally considered to be the invention of William Fairbairn
in 1844, although his patent was for the method of firing the furnaces alternately, so as to reduce smoke, rather than the boiler itself. Stephenson
's early 0-4-0
locomotive "Lancashire Witch
" had already demonstrated the use of twin furnace tubes within a boiler 15 years earlier.
Fairbairn had made a theoretical study of the thermodynamics of more efficient boilers, and it was this that had led him to increase the furnace
grate area relative to the volume of water. A particular reason for this was the so-far poor adoption of the Cornish boiler in the cotton mills of Lancashire, where the harder local coal couldn't be burned satisfactorily in the smaller furnace, in favour of the older low-pressure wagon boiler and its large grate.
The difficulties of the Cornish boiler were that a boiler of any particular power would require a known area of furnace tube as the heating area. Longer tubes required a longer and more expensive boiler shell. They also reduced the ratio of grate area relative to the heating area, making it difficult to maintain an adequate fire. Increasing the tube diameter reduced the depth of water covering the furnace tube and so increased the need for accurate control of water level by the fireman, or else the risk of boiler explosion
. Fairbairn's studies of hoop stress in cylinders also showed that smaller tubes were stronger than larger tubes. His solution was simple: to replace one large furnace tube with two smaller ones.
The patent showed another advantage of twin furnaces. By firing them alternately and closing the firebox door between firings, it was also possible to arrange a supply of air past the furnace (in the case of a Lancashire boiler, through the ashpan beneath the grate) which would encourage the flue gases produced by the fire to burn more completely and cleanly, thus reducing smoke and pollution. A key factor in this was the distinctive shuttered rotating air damper in the door, which became a feature from the 1840s.
The use of two flues also has a strengthening effect, acting as two long rod stays that support the end plates.
Later developments added Galloway tubes (after their inventor, patented in either 1848 or 1851) crosswise water tubes across the flue, thus increasing the heated surface area. As these are short tubes of large diameter and the boiler continues to use a relatively low pressure, this is still not considered to be a water-tube boiler
. The tubes are tapered, simply to make their installation through the flue easier.
Lancashire boilers often show corrugated flue
s, which absorb thermal expansion without straining the riveted seams. Another development was the "kidney
flue" or Galloway boiler, where the two furnaces join together into a single flue, kidney-shaped in cross-section. This widened and flat-topped flue was stayed by the use of Galloway tubes.
Although the Lancashire boiler is considered to be an antiquated design, provided that the flue is long enough it can be reasonably efficient. This does lead to a bulky boiler though, particularly for its length, and this has always limited its use to stationary installations. It was the standard boiler in Greater Manchester and Lancashire cotton mills
.
's work on the Lancashire boiler had demonstrated the efficiency virtues of multiple furnaces relative to a reduced water volume. It was also widely understood that higher steam pressures improved the efficiency of engines. Fairbairn's research on the strength of cylinders led him to design another improved boiler, based around far-smaller tube diameters, which would thus be able to operate at higher pressures, typically 150 psi (10.2 atm). This was the "five tube" boiler, whose five tubes were arranged in two nested pairs as water drum and furnace, with the remaining tube mounted above them as a separate steam drum. The water volume was extremely low compared to previous boiler designs, as the furnace tubes almost filled each of the water drums.
The boiler was successful according to its goals and provided two large furnaces in a small water capacity. The separate steam drum also aided the production of "dry" steam, without the carryover of water and risk of priming. However it was also complex to manufacture, and did not offer a great deal of heating area for the work involved. It was soon superseded by multi-tube boiler
s such as the locomotive and the Scotch
boilers.
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
used to make steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
, usually for the purpose of driving a steam engine
Steam engine
A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be...
. The design marked a transitional stage in boiler development, between the early haystack boilers and the later multi-tube fire-tube boiler
Fire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
s. A flued boiler is characterized by a large cylindrical boiler shell forming a tank of water, traversed by one or more large flue
Flue
A flue is a duct, pipe, or chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. In the United States, they are also known as vents and for boilers as breeching for water heaters and modern furnaces...
s containing the furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
. These boilers appeared around the start of the 19th century and some forms remain in service today. Although mostly used for static steam plants, some were used in early steam vehicles, railway locomotives and ships.
Flued boilers were developed in an attempt to raise steam pressures and improve engine efficiency. Early haystack designs of Watt
James Watt
James Watt, FRS, FRSE was a Scottish inventor and mechanical engineer whose improvements to the Newcomen steam engine were fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world.While working as an instrument maker at the...
's day were mechanically weak and often presented an unsupported flat surface to the fire. Boiler explosion
Boiler explosion
A boiler explosion is a catastrophic failure of a boiler. As seen today, boiler explosions are of two kinds. One kind is over-pressure in the pressure parts of the steam and water sides. The second kind is explosion in the furnace. Boiler explosions of pressure parts are particularly associated...
s, usually beginning with failure of this firebox plate, were common. It was known that an arched structure was stronger than a flat plate and so a large circular flue tube was placed inside the boiler shell. The fire itself was on an iron grating placed across this flue, with a shallow ashpan beneath to collect the non-combustible residue. This had the additional advantage of wrapping the heating surface closely around the furnace, but that was a secondary benefit.
Although considered as low-pressure (perhaps 25 psi (1.7 atm)) today, this was regarded as high pressure compared to its predecessors. This increase in pressure was a major factor in making locomotives (i.e. small self-moving vehicles) such as Trevithick's
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...
into a practical proposition.
Centre-flue boilers
John Blenkinsop
John Blenkinsop was an English mining engineer and an inventor of steam locomotives, who designed the first practical railway locomotive....
's locomotives for the Middleton railway
Middleton Railway
The Middleton Railway is the world's oldest continuously working railway. It was founded in 1758 and is now a heritage railway run by volunteers from The Middleton Railway Trust Ltd...
and Stephenson's Locomotion
Locomotion No 1
Locomotion No. 1 is an early British steam locomotive. Built by George and Robert Stephenson's company Robert Stephenson and Company in 1825, it hauled the first train on the Stockton and Darlington Railway on 27 September 1825....
.
This type of boiler is simple to manufacture and strong enough to support "high pressure" (for the period) steam with expansive working in the cylinders. There is also good gas flow through the large flue, so that the fire receives sufficient draught from the action of a tall chimney
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
alone. However it also has little heating area, so is inefficient and burns a large amount of coal.
Return-flue boilers
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...
, this may be done by using a U-shaped return flue that bends back on itself.
Richard Trevithick had already used a return flue with his first 1802 Pen-y-darren engine and 1803 Coalbrookdale
Coalbrookdale
Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. This is where iron ore was first smelted by Abraham Darby using easily mined "coking coal". The coal was drawn from drift mines in the sides...
locomotive design. These boilers were heavily built of cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
, short and flat-ended. His 1805 "Newcastle
Newcastle upon Tyne
Newcastle upon Tyne is a city and metropolitan borough of Tyne and Wear, in North East England. Historically a part of Northumberland, it is situated on the north bank of the River Tyne...
" locomotive (actually built in Gateshead
Gateshead
Gateshead is a town in Tyne and Wear, England and is the main settlement in the Metropolitan Borough of Gateshead. Historically a part of County Durham, it lies on the southern bank of the River Tyne opposite Newcastle upon Tyne and together they form the urban core of Tyneside...
) began to show one characteristic feature of the return-flued boiler, a prominent dome shape to resist steam pressure in the solid end opposite both furnace and chimney. In this case, the boilermaking, now of wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...
plates, must have been complicated by Trevithick's single long-travel horizontal cylinder (9 inch diameter × 36 inch stroke) which emerged through this domed end. This did make work easier for the fireman though, as he was no longer trying to reach a firedoor beneath the long crosshead of the piston.
William Hedley
William Hedley
William Hedley was one of the leading industrial engineers of the early 19th century, and was very instrumental in several major innovations in early railway development...
used this pattern of boiler for his 1813 locomotives Puffing Billy
Puffing Billy (locomotive)
Puffing Billy is an early railway steam locomotive, constructed in 1813-1814 by engineer William Hedley, enginewright Jonathan Forster and blacksmith Timothy Hackworth for Christopher Blackett, the owner of Wylam Colliery near Newcastle upon Tyne, in the United Kingdom. It is the world's oldest...
and Wylam Dilly
Wylam Dilly
Wylam Dilly is one of the two oldest surviving railway locomotives in the world; it was built circa 1815 by William Hedley and Timothy Hackworth. Wylam Dilly was initially designed for and used on the Wylam Waggonway to transport coal. It is currently on display in the Royal Museum in Edinburgh...
. Through the Wylam
Wylam
Wylam is a small village about west of Newcastle upon Tyne. It is located in the county of Northumberland.It is famous for the being the birthplace of George Stephenson, one of the early rail pioneers. George Stephenson's Birthplace is his cottage that can be found on the north bank of the...
colliery and its owner Christopher Blackett
Blackett of Wylam
The Blacketts of Wylam were a branch of the ancient family of Blackett of Hoppyland, County Durham, England and were related to the Blackett Baronets....
, Hedley would have been familiar with Trevithick's engine.
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 :...
's 0-6-0 Royal George of 1827 also used a return-flued boiler, although it is best known for its pioneering use of a deliberate blastpipe
Blastpipe
The blastpipe is part of the exhaust system of a steam locomotive that discharges exhaust steam from the cylinders into the smokebox beneath the chimney in order to increase the draught through the fire.- History :...
to encourage draught on the fire. His lighter weight 0-4-0 version for 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....
, Sans Pareil
Sans Pareil
Sans Pareil is a steam locomotive built by Timothy Hackworth which took part in the 1829 Rainhill Trials on the Liverpool and Manchester Railway, held to select a builder of locomotives...
was very similar. Even though they appeared antiquated as soon as the Trials were over, the Canadian Samson
Samson (locomotive)
The Samson is an English-built railroad steam locomotive made in 1838 that ran on the Albion Mines Railway in Nova Scotia, Canada. It is preserved at the Nova Scotia Museum of Industry in Stellarton, Nova Scotia and is the oldest locomotive in Canada....
of this pattern was built in 1838 and still in service in 1883.
Huber boilers
The last return-flue boilers constructed (other than some stationary boilers) are often considered to be those built by the HuberHuber
Huber is a surname of German origin. It derives from the German word Hube meaning hide, a unit of land a farmer might possess. It is in the top ten most common surnames in the German-speaking world, especially in Austria and Switzerland where it is the surname of approximately 0.3% of the...
Co. of Marion, Ohio
Marion, Ohio
Marion is a city in the U.S. state of Ohio and the county seat of Marion County. The municipality is located in north-central Ohio, approximately north of Columbus....
for their "New Huber" traction engine
Traction engine
A traction engine is a self-propelled steam engine used to move heavy loads on roads, plough ground or to provide power at a chosen location. The name derives from the Latin tractus, meaning 'drawn', since the prime function of any traction engine is to draw a load behind it...
s, from 1885 to 1903.
These were not, however, return-flue boilers in the sense used here, but rather return-tube boilers. They had a single large cylindrical furnace tube, a combustion chamber external to the boiler's pressure shell, then multiple, narrow fire-tubes returning to a horseshoe-shaped 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...
above and around the firedoor. The proximity of this smokebox to the fireman led to their nickname of "belly burners". Their design thus has more in common with the horizontal launch-type boiler
Launch-type boiler
A launch-type, gunboat or horizontal multitubular boiler is a form of small steam boiler. It consists of a cylindrical horizontal shell with a cylindrical furnace and fire-tubes within this....
s (as used by Sir Arthur Heywood
Eaton Hall Railway
The Eaton Hall Railway was an early gauge narrow gauge estate railway built in 1896 at Eaton Hall in Cheshire.It was built for the Duke of Westminster by Sir Arthur Percival Heywood, who had pioneered the fifteen inch gauge with his Duffield Bank Railway, and connected the hall to the GWR...
) or the Scotch marine boiler
Scotch marine boiler
A "Scotch" marine boiler is a design of steam boiler best known for its used on ships.The general layout is that of a squat horizontal cylinder. One or more large cylindrical furnaces are in the lower part of the boiler shell. Above this is a large number of small-diameter fire-tubes...
than they do with the simple single-flue boiler.
By this time, the locomotive boiler had become ubiquitous for traction engines. Compared to this, the advantage of the Huber boiler was that the firetubes could be replaced more easily, without needing to work from within an enclosed firebox.
Cornish boiler
The simplest form of flued boiler was Richard TrevithickRichard 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...
's "high-pressure" Cornish boiler, first installed at Dolcoath mine
Dolcoath mine
Dolcoath mine was a copper and tin mine in Camborne, Cornwall, in the United Kingdom. Its name derives from the Cornish for 'Old Ground', and it was also affectionately known as The Queen of Cornish Mines. The site is north-west of Carn Brea. Dolcoath Road runs between the A3047 road and Chapel Hill...
in 1812. This is a long horizontal cylinder with a single large flue containing the fire. As the furnace relied on natural draught, a tall chimney
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
was required at the far end of the flue to encourage a good supply of air (oxygen) to the fire.
For efficiency, Trevithick's innovation was to encase beneath the boiler with a brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...
-built chamber. Exhaust gases passed through the central flue and then routed outside and around the iron boiler shell. To keep the chimney clear of the firing space, the brick flue passed first underneath the centre of the boiler to the front face, then back again along the sides and to the chimney.
Cornish boilers had several advantages over the preceding wagon boilers: they were composed of mostly curved surfaces, better to resist the pressure. Their flat ends were smaller than the flat sides of the wagon boiler and were stayed by the central furnace flue, and sometimes by additional long rod stays. A less obvious advantage was that of boiler scale. Wagon or haystack boilers were heated from beneath and any scale or impurities that formed a sediment settled upon this plate, insulating it from the water. This reduced heating efficiency and could in extremis lead to local overheating and failure of the boiler plates. In the flued boiler, any sediment fell past the furnace flue and settled out at the bottom of the boiler shell, where it had less effect.
In model engineering
Model engineering
Model engineering is the hobby of constructing machines in miniature. The term was in use by 1888. There is some debate about the appropriateness of the term...
, the Cornish boiler, particularly when fitted with Galloway tubes (see Lancashire Boiler, below), is an excellent choice for gas-fired boilers and model steam boats. It is simple to build and as efficient as any small-scale boiler.
Butterley boiler
The Butterley or "whistle mouth" boiler is a little-known design derived from the Cornish pattern, produced by the noted Butterley boilerworks of Derbyshire. It is basically a Cornish boiler with the lower half of the shell around the furnace removed, so as to permit a large fire to be lit. This made it popular in the textile mills of the PenninesPennines
The Pennines are a low-rising mountain range, separating the North West of England from Yorkshire and the North East.Often described as the "backbone of England", they form a more-or-less continuous range stretching from the Peak District in Derbyshire, around the northern and eastern edges of...
, where the hard Northern coal was of less calorific value than the Welsh coal used in the South West and required a larger fire. Alternatively it may be considered as a shortened Cornish boiler with a waggon boiler placed in front of it with a larger fire beneath that. It suffers the same drawback as the wagon boiler: the concave firebox plate is mechanically weak and this either limits the working pressure or requires extra mechanical staying.
Lancashire boiler
William Fairbairn
Sir William Fairbairn, 1st Baronet was a Scottish civil engineer, structural engineer and shipbuilder.-Early career:...
in 1844, although his patent was for the method of firing the furnaces alternately, so as to reduce smoke, rather than the boiler itself. Stephenson
Robert Stephenson
Robert Stephenson FRS was an English civil engineer. He was the only son of George Stephenson, the famed locomotive builder and railway engineer; many of the achievements popularly credited to his father were actually the joint efforts of father and son.-Early life :He was born on the 16th of...
's early 0-4-0
0-4-0
Under the Whyte notation for the classification of steam locomotives, 0-4-0 represents one of the simplest possible types, that with two axles and four coupled wheels, all of which are driven...
locomotive "Lancashire Witch
Lancashire Witch
Lancashire Witch was an early steam locomotive built by Robert Stephenson and Company in Newcastle-upon-Tyne in 1828. It was a development of Locomotion.-Description:...
" had already demonstrated the use of twin furnace tubes within a boiler 15 years earlier.
Fairbairn had made a theoretical study of the thermodynamics of more efficient boilers, and it was this that had led him to increase the furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
grate area relative to the volume of water. A particular reason for this was the so-far poor adoption of the Cornish boiler in the cotton mills of Lancashire, where the harder local coal couldn't be burned satisfactorily in the smaller furnace, in favour of the older low-pressure wagon boiler and its large grate.
The difficulties of the Cornish boiler were that a boiler of any particular power would require a known area of furnace tube as the heating area. Longer tubes required a longer and more expensive boiler shell. They also reduced the ratio of grate area relative to the heating area, making it difficult to maintain an adequate fire. Increasing the tube diameter reduced the depth of water covering the furnace tube and so increased the need for accurate control of water level by the fireman, or else the risk of boiler explosion
Boiler explosion
A boiler explosion is a catastrophic failure of a boiler. As seen today, boiler explosions are of two kinds. One kind is over-pressure in the pressure parts of the steam and water sides. The second kind is explosion in the furnace. Boiler explosions of pressure parts are particularly associated...
. Fairbairn's studies of hoop stress in cylinders also showed that smaller tubes were stronger than larger tubes. His solution was simple: to replace one large furnace tube with two smaller ones.
The patent showed another advantage of twin furnaces. By firing them alternately and closing the firebox door between firings, it was also possible to arrange a supply of air past the furnace (in the case of a Lancashire boiler, through the ashpan beneath the grate) which would encourage the flue gases produced by the fire to burn more completely and cleanly, thus reducing smoke and pollution. A key factor in this was the distinctive shuttered rotating air damper in the door, which became a feature from the 1840s.
The use of two flues also has a strengthening effect, acting as two long rod stays that support the end plates.
Later developments added Galloway tubes (after their inventor, patented in either 1848 or 1851) crosswise water tubes across the flue, thus increasing the heated surface area. As these are short tubes of large diameter and the boiler continues to use a relatively low pressure, this is still not considered to be a water-tube boiler
Water-tube boiler
A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...
. The tubes are tapered, simply to make their installation through the flue easier.
Lancashire boilers often show corrugated flue
Leeds Forge Company
The Leeds Forge Company manufactured corrugated furnaces for marine boilers and later, pressed steel railway vehicles, in Leeds, England.- Early history :The company was founded by Samson Fox, who was born in Bradford in 1838...
s, which absorb thermal expansion without straining the riveted seams. Another development was the "kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
flue" or Galloway boiler, where the two furnaces join together into a single flue, kidney-shaped in cross-section. This widened and flat-topped flue was stayed by the use of Galloway tubes.
Although the Lancashire boiler is considered to be an antiquated design, provided that the flue is long enough it can be reasonably efficient. This does lead to a bulky boiler though, particularly for its length, and this has always limited its use to stationary installations. It was the standard boiler in Greater Manchester and Lancashire cotton mills
Cotton mill
A cotton mill is a factory that houses spinning and weaving machinery. Typically built between 1775 and 1930, mills spun cotton which was an important product during the Industrial Revolution....
.
Fairbairn's five-tube boiler
William FairbairnWilliam Fairbairn
Sir William Fairbairn, 1st Baronet was a Scottish civil engineer, structural engineer and shipbuilder.-Early career:...
's work on the Lancashire boiler had demonstrated the efficiency virtues of multiple furnaces relative to a reduced water volume. It was also widely understood that higher steam pressures improved the efficiency of engines. Fairbairn's research on the strength of cylinders led him to design another improved boiler, based around far-smaller tube diameters, which would thus be able to operate at higher pressures, typically 150 psi (10.2 atm). This was the "five tube" boiler, whose five tubes were arranged in two nested pairs as water drum and furnace, with the remaining tube mounted above them as a separate steam drum. The water volume was extremely low compared to previous boiler designs, as the furnace tubes almost filled each of the water drums.
The boiler was successful according to its goals and provided two large furnaces in a small water capacity. The separate steam drum also aided the production of "dry" steam, without the carryover of water and risk of priming. However it was also complex to manufacture, and did not offer a great deal of heating area for the work involved. It was soon superseded by multi-tube boiler
Fire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
s such as the locomotive and the Scotch
Scotch marine boiler
A "Scotch" marine boiler is a design of steam boiler best known for its used on ships.The general layout is that of a squat horizontal cylinder. One or more large cylindrical furnaces are in the lower part of the boiler shell. Above this is a large number of small-diameter fire-tubes...
boilers.