Three-drum boilers
Encyclopedia
Three-drum boilers are a class of water-tube boiler
used to generate steam, typically to power ships. They are compact and of high evaporative power, factors that encourage this use. Other boiler designs may be more efficient, although bulkier, and so the three-drum pattern was rare as a land-based stationary boiler.
The fundamental characteristic of the "three-drum" design is the arrangement of a steam drum
above two water drum
s, in a triangular layout. Water tubes fill in the two sides of this triangle between the drums, and the furnace
is in the centre. The whole assembly is then enclosed in a casing, leading to the exhaust flue
.
Firing can be by either coal or oil. Many coal-fired boilers used multiple firedoors and teams of stokers, often from both ends.
Development of the three-drum boiler began in the late 19th century, with the demand from naval ships that required high power and a compact boiler. The move to water-tube boilers had already begun, with designs such as the Babcock & Wilcox or the Belleville. The three-drum arrangement was lighter and more compact for the same power.
The new generation of "small-tube" water-tube boilers used water-tubes of around 2 inches (5 cm) diameter, compared to older designs of 3 or 4 inches. This gave a greater ratio of tube surface heating area to the tube volume, thus more rapid steaming. These small-tube boilers also became known as "express" boilers. Although not all of these were three-drum designs (notably the Thornycroft), most were some variation of this. As the tubes of the three-drum are close to vertical (compared to the Babcock & Wilcox), this encourages strong circulation by the thermosyphon effect, further encouraging steaming.
Some of the first boiler tubes, particularly the Du Temple with its sharp corners, could not be cleaned of scale internally. Tubes were later cleaned internally by attempting to pass a hinged rod through, with a brush at the end. For the curved tube designs, often only part of the tube could be reached. Another method was to pass a chain down the tube from above, pulling a brush behind it, although this was unworkable for boilers like the Thornycroft where the tubes first travelled horizontally or upwards. The eventual method was to use 'bullet' brushes that were fired from one drum into the other by use of compressed air. Sets of brushes were used, one for each tube, and they were carefully numbered and counted afterwards to ensure that none had been left behind, blocking a tube.
within the tube bank, so as to encourage the necessary temperature difference.
, patented in 1876. It was invented by Du Temple in France and also tested in a Royal Navy torpedo gunboat
. Water tubes were convoluted, arranged in four rows to a bank, and S-shaped with sharp right angle bends. This packed a large tube heating area into a small volume, but made tube cleaning impractical. The drums were cylindrical, with perpendicular tube entry and external downcomers between them.
Downcomers were used, either the usual two large pipes, or an unusual but characteristic arrangement of four small 4 inches (10 cm) tubes to each drum. This was a feature intended to improve survivability after damage, when used on-board warships. The boiler could remain in service with a damaged downcomer tube plugged.
The mud drums were raised above the floor of the furnace on steel girder stools, increasing the furnace volume available for combustion. This feature was intended to encourage the use of oil burning, an innovation on warships around this time. The general appearance of the White-Forster is similar to that of the later Admiralty pattern. Features such as the raised mud drums and the shape of the tubes were an influence.
White-Forster boilers were introduced into the Royal Navy from 1906, for light cruiser
s and torpedo boat destroyers.
. It was used by the navies of several nations, notably those of France, Russia, Britain and United States. In 1896, the Royal Navy had them installed in twenty-six boats, more than any other water-tube design.
Initial design of the Normand boiler was as a development of the Du Temple, with the sharp corners of the tubes replaced by a smooth radiused bend, but still retaining the S shape.
The design of the Normand gave a particularly large heating area (tube surface area) in relation to the grate area. The cost of this was a dense nest of tubes, where each of the numerous rows of tubes was bent into a different and complex shape. Tube ends entered the cylindrical drums perpendicular, for good sealing. The space needed for all these tubes filled the entire lower half of the steam drum, requiring both a large drum, and also a separate steam dome
from which to collect dry steam. The external boiler casing entered the flue uptake at one end, usually enclosing this dome. The ends of the drums extended outside the casing as hemispherical domes. Cold downcomers outside the casing linked these drums, providing a path for the return circulation of cold water.
A further development was the Normand-Sigaudy, where two Normand boilers were coupled back-to-back, for use in large ships. This effectively gave a double-ended Normand (as was later common with the Yarrow) that could be fired from both ends.
boiler is a variant that splits the usual central furnace into two. There are four drums: two main drums vertically in the centre – a steam and a water drum – also two wing drums at the outside edges of the furnace. The design was notable for its early use of the water-wall furnace. The outer bank of tubes was shallow, consisting of only two rows of tubes. These rows were spaced closely, so that the tubes formed a solid wall, without gasflow between them. The inner bank of tubes was similar: the two rows of tubes closest to the furnace formed a similar water wall. These tubes were splayed apart at their base, so as to provide space for gasflow between them. Within the tube bank, gas flow is mostly parallel to the tubes, similar to some early designs, but contrary to the crossflow design of later three-drum boilers. The exhaust gas emerged into the heart-shaped space below the upper central drum, exiting to the funnel through the rear wall.
The steam drum is circular, with perpendicular tube entry. The tube ends span a considerable circumference of the drum, so that the upper tubes enter above the water level. They are thus 'non-drowned' tubes.
The upper and lower central drums are linked by downcomers. Unusually these are internal to the boiler and are heated, although not strongly, by the exhaust gases. They are formed as several (eight or nine) 4 inches (10 cm) vertical tubes on the centreline of the boiler. They are formed into a shallow S-shape to give a little flexibility against thermal expansion. The small wing drums are connected to the lower central drum alone, by large external pipes outside the rear casing of the boiler.
Owing to its early use in the Thornycroft-built destroyer HMS Daring
of 1893, this design became known as the 'Daring' boiler.
A small single-sided version of this boiler was also produced for launches. The first small version of this also dispensed with the wing drum, the water-wall tubes bending at right angles and passing back to the central water drum, the tubes also forming the grate to support the fire.
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Later designs, the Thornycroft-Schulz pattern, made the outer wings more important. The number of their tubes was increased, such that they became the majority of the heating surface and also the main gas path for the exhaust gases. The wing drums became large enough to permit a man access inside, for cleaning and expanding new tubes into place.
The earlier Thornycroft-Marshall design of water-tube boiler used horizontal hairpin water-tubes fitted into sectional headers. It has little relation to the types described here.
Alfred Yarrow
developed his boiler as a response to other water-tube designs, and his perception in 1877 that Yarrow & Co
were lagging behind other shipbuilders. His initial thoughts already defined the key features of the design, a three-drum boiler with straight tubes, yet it took ten years of research before the first boiler was supplied for a torpedo boat
of 1887.
Yarrow recognised that the temperature of the water-tubes was held relatively low and was consistent amongst them, provided that they remained full of water and boiling was not allowed to occur within the tubes themselves, i.e. they would remain as drowned tubes. High temperatures and variations only arose when tubes became steam filled, which also disrupted circulation.
His conclusion was thus that straight water-tubes were acceptable, and these would have obvious advantages for manufacture and cleaning in service.
Alfred Yarrow
conducted a famous experiment where he disproved this assumption. A vertical U-shaped tube was arranged so that it could be heated by a series of Bunsen burner
s on each side.
When only one side of the U was heated, there was the expected upward flow of heated water in that arm of the tube.
When heat was also applied to the unheated arm, conventional theory predicted that the circulatory flow would slow or stop completely. In practice, the flow actually increased. Provided that there was some asymmetry to the heating, Yarrow's experiment showed that circulation could continue and heating of the cooler downcomer could even increase this flow.
The Yarrow boiler could thus dispense with separate external downcomers. Flow was entirely within the heated watertubes, upwards within those closest to the furnace and downwards through those in the outer rows of the bank.
The first Yarrow water drums or "troughs" were D-shaped with a flat tubeplate, so as to provide an easy perpendicular mounting for the tubes. The tubeplate was bolted to the trough and could be dismantled for maintenance and tube cleaning.
This D shape is not ideal for a pressure drum though, as pressure will tend to distort it into a more circular section. This flexing led to leakage where the water tubes entered the drum; a problem, termed 'wrapperitis', which was shared with the White-Forster. Experience of boiler explosion
s had shown that sharp internal corners inside boilers were also prone to erosion by grooving. Later boilers used a more rounded section, although still asymmetrical rather than fully cylindrical.
The circulation in a Yarrow boiler depended on a temperature difference between the inner and outer tube rows of a bank, and particularly upon the rates of boiling. Whilst this is easy to maintain at low powers, a higher pressure Yarrow boiler will tend to have less temperature difference and thus will have less effective circulation. Some later and higher-pressure boilers were fitted with external downcomers, outside of the heated flue area.
When superheating
was adopted, primarily for use with steam turbine
s after 1900, the first Yarrow boilers placed their superheater coil outside of the main tube bank. Later designs became asymmetrical, with the tube bank on one side doubled and a hairpin-tube superheater placed between them.
, the lead ship of the Havock class destroyer
s, was built with the then current form of locomotive boiler; its sister ship HMS Hornet
with a Yarrow boiler for comparison. The trials were successful and the Yarrow boiler was adopted for naval service, particularly in small ships. In time the Navy would develop its own Admiralty pattern of three-drum boiler.
of Colchester
, intended for use in smaller boats. The tube banks separated into two groups, with the short tubes slightly curved away from each other. Entry into the lower water drum was perpendicular, requiring an almost rectangular drum with the tubes entering on separate faces. The mechanical weakness of such a shape was acceptable in this small size, but limited the boiler's potential. The casing was small and only enclosed part of the upper steam drum, leading directly to a funnel. A single inverted tee-shaped downcomer linked the drums at the rear of the boiler.
for their larger railway locomotives. It resembled most other three-drum designs, having almost-straight tubes. Its distinguishing feature was a firebrick wall two-thirds of the way down the furnace. The furnace grate was on the longer side of this, with the combustion gases passing out through the tube bank, along inside a steel outer casing, then back within the shorter tube bank. Coiled tube superheaters were placed in the gas flow outside of the tubes. The combustion gases thus passed through the tube bank twice, once outwards and then again inwards. A single central chimney exhausted from the centre of the far end, not as usual from outside the tubes. The relative temperature difference between gas passage through the two sections of the bank led to a circulation current that was upwards through the first, hotter, part of the bank and downwards through the further, less hot, bank. Circulation was also controlled by an internal weir plate within the upper water drum, so as to keep a depth of water above the ends of the hotter tubes, thus avoiding overheating of dry tubes.
Sentinel used the Woolnough boiler on a number of their larger locomotives, instead of their usual small vertical boiler
. These included railcar
s for the LNER and LMS
. Sentinel's best-known use of the Woolnough was for the 'Colombian' articulated locomotive
s. These were a series of four, metre gauge
locomotives of Co-Co wheel arrangement, built in 1934. They ran at the unusually high pressure
of 550 psi and each axle was driven by a separate steam engine, designed by Abner Doble
. The first was supplied to Belgian Railways, the following three were built for the Société National des Chemins de Fer en Colombe
of Colombia
, but first shipped to Belgium for testing. Most photographs that exist of these locomotives were taken in Belgium. Little is known of their history after arrival in Colombia.
between the First
and Second
World Wars. Much of the design work was conducted at Admiralty Fuel Experimental Stationinitially the "Admiralty Liquid Fuel Experimentation Station", later the Admiralty Marine Engineering Establishment at Haslar
and the first boilers were installed in three of the A class destroyers
of 1927. These boilers established new Royal Navy standard operating conditions for boilers of 300 psi / 600 °F (315.6 °C).
The design was broadly similar to later, high-pressure and oil-fired, versions of the Yarrow. The waterdrums were cylindrical and downcomers were sometimes, but not always, used. The only major difference was in the tube banks. Rather than straight tubes, each tube was mostly straight, but slightly cranked towards their ends. These were installed in two groups within the bank, so that they formed a gap between them within the bank. Superheaters were placed inside this gap and hung by hooks from the steam drum. The advantage of placing the superheaters here was that they increased the temperature differential between the inner and outer tubes of the bank, thus encouraging circulation. In the developed form, the boiler had four rows of tubes on the furnace-side of the superheater and thirteen for the outer-side.
before the water re-circulated down the outer-side tubes. In a manner similar to work taking place around the same time on the LMS railway
and the development of top feed for steam locomotive
s, the feedwater was also routed upwards through 'spray pots' and thus passed through the steam space as droplets. The cold feedwater was thus heated to the same temperature as the boiler water before mixing with it, avoiding disturbance to the circulation path.Although there is no record of any shared development here, between the Royal Navy and the LMS railway
, the two solutions represent an example of parallel evolution
in response to the same problem. As boiler pressure increases, the saturation temperature of wet steam and thus the circulating water increases, making it more sensitive to disruption by cold feedwater.
performance was disappointing. Superheat at full power was limited deliberately to 100 °F (37.8 °C) so as to avoid reliability problems, which then meant that it was ineffective at low powers. Development work by Babcock & Wilcox resolved this by increasing the steam flow speed through the superheater to 150 ft/sec, avoiding the problems of tube distortion and metallurgical failure. New boilers for the Nelson class battleship
s and the Kent class cruisers could achieve a superheat of 200–250 °F (93.3–121.1 °C) throughout the operating power range at 250 psi.
From 1929, Hawthorn Leslie constructed a trial boiler with a partial water-wall to the rear of the furnace. Unlike other water-wall designs, this additional water drum spanned only the centre of the furnace, the vertical tubes were enclosed in a refractory
casing and did not form a closely packed solid wall. The concern was that a full water-wall would unbalance the existing header arrangement of the three-drum boiler, which indeed showed to be the case. Excess steam production at the rear of the steam drum led to disrupted circulation and a problem with priming
. The development of water-walls for this type of boiler was abandoned, although trials did continue with which was trialled with a single water-wall Johnson boiler replacing one of its three three-drum boilers.
was Nigel Gresley
's experimental Engine 10000 of 1924 for the LNER
company. Having observed the benefits of higher pressures and compound engines in marine practice
, Gresley was keen to experiment with this approach in a railway locomotive
. As with the land-based boilers, Harold Yarrow was keen to expand the market for Yarrow's boiler.
The boiler was not the usual Yarrow design, and although designed by Yarrow was built by the Sheffield-based arm of the John Brown
shipyard. In operation, particularly its circulation paths, the boiler had more in common with other three-drum designs such as the Woolnough.
Working pressure was of 450 pound per square inches (31 bar) as opposed to the 180 pound per square inches (12 bar) of the contemporary Gresley A1 locomotive
s.
The boiler resembled two elongated marine Yarrow boiler
s, placed end to end. Both had the usual Yarrow arrangement of a central large steam drum above two separated water drums, linked by four rows of slightly curved tubes. The upper drum was shared, but the lower water drums were separate. The rearward "firebox" area was wide and spanned the frames
, placing the water drums at the limits of the loading gauge
. The forward "boiler" region was narrow-set, with its water drums placed between the frames. Although the outer casings were of similar width, the tube banks for the forward section were much closer. The space outboard of the tubes formed a pair of exhaust flues leading forwards. A large space outside these flue walls but inside the boiler casing was used as an air duct from the air inlet, a crude rectangular slot beneath the smokebox door, which had the effect of both pre-heating the combustion air and also cooling the outer casing to prevent overheating. Longitudinal superheater
tubes were placed in the central space between the steam generating tubes. The third area forwards contained superheater headers, the regulators and the smokebox, but no deliberate heating surface. The external boiler casing remained at much the same width throughout, giving an overall triangular, but curved, appearance. The lower edge of each section stepped upwards, and was obvious externally.
Firing was with coal, at just one end through a conventional locomotive single firedoor, and a single manual fireman. Owing to the single-ended firing and the predominantly longitudinal gasflow, compared to the Yarrow's normal through-bank gasflow, there was a pronounced temperature difference between the front and back of the boiler. This led to the water circulation currents, especially in the second section, to be longitudinal through the water drums, like the Woolnough, rather than the usual Yarrow. The first section, which included some water-tubes to the rear wall, was radiant heated and effectively a water-wall furnace, without any gas flow through the tube bank. Despite this, it still used four rows of tubes. The second section had its gasflow arranged by steel and firebrick baffles so that the combustion gases entered through the centre and passed through the tube banks into the side flues, giving better convective heat transfer.
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...
used to generate steam, typically to power ships. They are compact and of high evaporative power, factors that encourage this use. Other boiler designs may be more efficient, although bulkier, and so the three-drum pattern was rare as a land-based stationary boiler.
The fundamental characteristic of the "three-drum" design is the arrangement of a steam drum
Steam drum
A steam drum is a standard feature of a water-tube boiler. It is a reservoir of water/steam at the top end of the water tubes. The drum stores the steam generated in the water tubes and acts as a phase-separator for the steam/water mixture...
above two water drum
Water drum
Water drums are a category of membranophone characterized by the filling of the drum chamber with some amount of water to create a unique sound. Water drums are common in Native American music, and in some forms of African and Southeast Asian music....
s, in a triangular layout. Water tubes fill in the two sides of this triangle between the drums, and 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...
is in the centre. The whole assembly is then enclosed in a casing, leading to the exhaust 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...
.
Firing can be by either coal or oil. Many coal-fired boilers used multiple firedoors and teams of stokers, often from both ends.
Development of the three-drum boiler began in the late 19th century, with the demand from naval ships that required high power and a compact boiler. The move to water-tube boilers had already begun, with designs such as the Babcock & Wilcox or the Belleville. The three-drum arrangement was lighter and more compact for the same power.
The new generation of "small-tube" water-tube boilers used water-tubes of around 2 inches (5 cm) diameter, compared to older designs of 3 or 4 inches. This gave a greater ratio of tube surface heating area to the tube volume, thus more rapid steaming. These small-tube boilers also became known as "express" boilers. Although not all of these were three-drum designs (notably the Thornycroft), most were some variation of this. As the tubes of the three-drum are close to vertical (compared to the Babcock & Wilcox), this encourages strong circulation by the thermosyphon effect, further encouraging steaming.
Development
The development of the three-drum pattern was generally one of simplification, rather than increasing complexity or sophistication. Even the first boilers packed a large heating area into a compact volume, their difficulty was in manufacturing and particularly for their maintenance on-board ship.Tubes
The convoluted tubes of early designs such as the Du Temple and Normand were the first to go. A multi-row bank of tubes could provide adequate heating area, without this complexity. Tubes also became straighter, mostly to ease their cleaning. Yarrow had demonstrated that straight tubes did not cause any problems with expansion, but circular drums and perpendicular tube entry were both valuable features for a long service life. Where tubes entered drums at an angle, heating and cooling tended to bend the tube back and forth, leading to leaks. A perpendicular entry was easier to expand the tubes for a reliable seal and also avoided these sideways stresses. It was worth the compromise of the Admiralty boiler's bent tube ends to keep these two features, and these tubes were still simple enough in shape to clean easily.Some of the first boiler tubes, particularly the Du Temple with its sharp corners, could not be cleaned of scale internally. Tubes were later cleaned internally by attempting to pass a hinged rod through, with a brush at the end. For the curved tube designs, often only part of the tube could be reached. Another method was to pass a chain down the tube from above, pulling a brush behind it, although this was unworkable for boilers like the Thornycroft where the tubes first travelled horizontally or upwards. The eventual method was to use 'bullet' brushes that were fired from one drum into the other by use of compressed air. Sets of brushes were used, one for each tube, and they were carefully numbered and counted afterwards to ensure that none had been left behind, blocking a tube.
Downcomers
Separate downcomers were used by most designs, even after Yarrow's experiments had demonstrated that circulation could still take place amongst the heated tubes alone. Again, the Admiralty boiler (which omitted downcomers) was the culmination of this approach, placing the superheaterSuperheater
A superheater is a device used to convert saturated steam or wet steam into dry steam used for power generation or processes. There are three types of superheaters namely: radiant, convection, and separately fired...
within the tube bank, so as to encourage the necessary temperature difference.
Furnaces
The Admiralty boiler is usually considered to be a direct evolution of the Yarrow, although the White-Forster also had an influence, probably as a result of the large number in service with the Royal Navy. The circular water drums, and their raising above the furnace floor, are White-Forster features. The first reduces the risk of grooving, the latter is appropriate for oil firing.Du Temple boiler
The Du Temple was an early naval water-tube boilerWater-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...
, patented in 1876. It was invented by Du Temple in France and also tested in a Royal Navy torpedo gunboat
Torpedo gunboat
In late 19th-century naval terminology, torpedo gunboats or, in north European usage, torpedo cruisers, were a form of gunboat armed with torpedoes and designed for hunting and destroying smaller torpedo boats...
. Water tubes were convoluted, arranged in four rows to a bank, and S-shaped with sharp right angle bends. This packed a large tube heating area into a small volume, but made tube cleaning impractical. The drums were cylindrical, with perpendicular tube entry and external downcomers between them.
White-Forster boiler
The White-Forster was of simple construction, with tubes that had only a gentle curvature to them. This was sufficient to allow them to be replaced in-situ, working through the manhole at the end of the large steam drum. Each tube was sufficiently curved to allow it to be extracted through the steam drum, but sufficiently straight that a single tube could be replaced from a tube bank, without requiring other tubes to be removed so as to permit access. This was one of many features of the White-Forster intended to make it reliable in naval service and easy to maintain. These tubes were of particularly small diameter, only 1 inches (2.5 cm) and especially numerous, a total of 3,744 being used in some boilers. The tubes were arranged in 24 rows to a bank, each requiring a different length of tube, and 78 rows per drum. All tubes were curved to the same radius, facilitating repair and replacement on-board, but requiring the tube holes in the drums to be reamed to precise angles on a jig during manufacture. This small tube diameter gave a high heating surface, but probably too much: the ratio of surface to volume became excessive and gas flow through the tube banks was affected, giving the boiler furnaces something of a reputation as poor burners.Downcomers were used, either the usual two large pipes, or an unusual but characteristic arrangement of four small 4 inches (10 cm) tubes to each drum. This was a feature intended to improve survivability after damage, when used on-board warships. The boiler could remain in service with a damaged downcomer tube plugged.
The mud drums were raised above the floor of the furnace on steel girder stools, increasing the furnace volume available for combustion. This feature was intended to encourage the use of oil burning, an innovation on warships around this time. The general appearance of the White-Forster is similar to that of the later Admiralty pattern. Features such as the raised mud drums and the shape of the tubes were an influence.
White-Forster boilers were introduced into the Royal Navy from 1906, for light cruiser
Light cruiser
A light cruiser is a type of small- or medium-sized warship. The term is a shortening of the phrase "light armored cruiser", describing a small ship that carried armor in the same way as an armored cruiser: a protective belt and deck...
s and torpedo boat destroyers.
Normand boiler
The Normand boiler was developed by the French Normand shipyard of le HavreLe Havre
Le Havre is a city in the Seine-Maritime department of the Haute-Normandie region in France. It is situated in north-western France, on the right bank of the mouth of the river Seine on the English Channel. Le Havre is the most populous commune in the Haute-Normandie region, although the total...
. It was used by the navies of several nations, notably those of France, Russia, Britain and United States. In 1896, the Royal Navy had them installed in twenty-six boats, more than any other water-tube design.
Initial design of the Normand boiler was as a development of the Du Temple, with the sharp corners of the tubes replaced by a smooth radiused bend, but still retaining the S shape.
The design of the Normand gave a particularly large heating area (tube surface area) in relation to the grate area. The cost of this was a dense nest of tubes, where each of the numerous rows of tubes was bent into a different and complex shape. Tube ends entered the cylindrical drums perpendicular, for good sealing. The space needed for all these tubes filled the entire lower half of the steam drum, requiring both a large drum, and also a separate steam dome
Steam dome
A Steam dome is a vessel fitted to the top of the boiler of a steam locomotive. It contains the opening to the main steam pipe and its purpose is to allow this opening to be kept well above the water level in the boiler...
from which to collect dry steam. The external boiler casing entered the flue uptake at one end, usually enclosing this dome. The ends of the drums extended outside the casing as hemispherical domes. Cold downcomers outside the casing linked these drums, providing a path for the return circulation of cold water.
A further development was the Normand-Sigaudy, where two Normand boilers were coupled back-to-back, for use in large ships. This effectively gave a double-ended Normand (as was later common with the Yarrow) that could be fired from both ends.
Thornycroft boiler
The ThornycroftJohn I. Thornycroft & Company
John I. Thornycroft & Company Limited, usually known simply as Thornycroft was a British shipbuilding firm started by John Isaac Thornycroft in the 19th century.-History:...
boiler is a variant that splits the usual central furnace into two. There are four drums: two main drums vertically in the centre – a steam and a water drum – also two wing drums at the outside edges of the furnace. The design was notable for its early use of the water-wall furnace. The outer bank of tubes was shallow, consisting of only two rows of tubes. These rows were spaced closely, so that the tubes formed a solid wall, without gasflow between them. The inner bank of tubes was similar: the two rows of tubes closest to the furnace formed a similar water wall. These tubes were splayed apart at their base, so as to provide space for gasflow between them. Within the tube bank, gas flow is mostly parallel to the tubes, similar to some early designs, but contrary to the crossflow design of later three-drum boilers. The exhaust gas emerged into the heart-shaped space below the upper central drum, exiting to the funnel through the rear wall.
The steam drum is circular, with perpendicular tube entry. The tube ends span a considerable circumference of the drum, so that the upper tubes enter above the water level. They are thus 'non-drowned' tubes.
The upper and lower central drums are linked by downcomers. Unusually these are internal to the boiler and are heated, although not strongly, by the exhaust gases. They are formed as several (eight or nine) 4 inches (10 cm) vertical tubes on the centreline of the boiler. They are formed into a shallow S-shape to give a little flexibility against thermal expansion. The small wing drums are connected to the lower central drum alone, by large external pipes outside the rear casing of the boiler.
Owing to its early use in the Thornycroft-built destroyer HMS Daring
HMS Daring (1893)
HMS Daring and HMS Decoy together made up the Daring-class of torpedo boat destroyers which served with the Royal Navy during the turn of the 19th and 20th centuries. They differed from the later Ardent class only in the provision of a bow mounted torpedo tube, which was later removed...
of 1893, this design became known as the 'Daring' boiler.
A small single-sided version of this boiler was also produced for launches. The first small version of this also dispensed with the wing drum, the water-wall tubes bending at right angles and passing back to the central water drum, the tubes also forming the grate to support the fire.
Thornycroft-Schulz boiler
The earlier Thornycroft-Marshall design of water-tube boiler used horizontal hairpin water-tubes fitted into sectional headers. It has little relation to the types described here.
Yarrow boiler
The Yarrow boiler design is characterised by its use of straight water-tubes, without downcomers. Circulation, both upwards and downwards, occurs within this same tube bank.Alfred Yarrow
Alfred Yarrow
Sir Alfred Fernandez Yarrow, 1st Baronet, of Homestead was a British shipbuilder who started a shipbuilding dynasty, Yarrow Shipbuilders.-Life and career:...
developed his boiler as a response to other water-tube designs, and his perception in 1877 that Yarrow & Co
Yarrow Shipbuilders
Yarrow Limited , often styled as simply Yarrows, was a major shipbuilding firm based in the Scotstoun district of Glasgow on the River Clyde...
were lagging behind other shipbuilders. His initial thoughts already defined the key features of the design, a three-drum boiler with straight tubes, yet it took ten years of research before the first boiler was supplied for a torpedo boat
Torpedo boat
A torpedo boat is a relatively small and fast naval vessel designed to carry torpedoes into battle. The first designs rammed enemy ships with explosive spar torpedoes, and later designs launched self-propelled Whitehead torpedoes. They were created to counter battleships and other large, slow and...
of 1887.
Straight tubes
Early water-tube designers had been concerned with the expansion of the boiler's tubes when heated. Efforts were made to permit them to expand freely, particularly so that those closest to the furnace might expand relatively more than those further away. Typically this was done by arranging the tubes in large looping curves. These had difficulties in manufacturing and required support in use.Yarrow recognised that the temperature of the water-tubes was held relatively low and was consistent amongst them, provided that they remained full of water and boiling was not allowed to occur within the tubes themselves, i.e. they would remain as drowned tubes. High temperatures and variations only arose when tubes became steam filled, which also disrupted circulation.
His conclusion was thus that straight water-tubes were acceptable, and these would have obvious advantages for manufacture and cleaning in service.
Yarrow's circulation experiments
It was already recognised that a water-tube boiler relied on a continuous flow through the water-tubes, and that this must be by a thermosyphon effect rather than requiring an impractical pump. Forced-circulation boilers with pumps, such as the Velox, would not appear for another thirty years and even then they would be initially unreliable. The assumption was that flow through the water-tubes would be upwards, owing to their heating by the furnace, and that the counterbalancing downward flow would require external unheated downcomers.Alfred Yarrow
Alfred Yarrow
Sir Alfred Fernandez Yarrow, 1st Baronet, of Homestead was a British shipbuilder who started a shipbuilding dynasty, Yarrow Shipbuilders.-Life and career:...
conducted a famous experiment where he disproved this assumption. A vertical U-shaped tube was arranged so that it could be heated by a series of Bunsen burner
Bunsen burner
A Bunsen burner, named after Robert Bunsen, is a common piece of laboratory equipment that produces a single open gas flame, which is used for heating, sterilization, and combustion.- Operation:...
s on each side.
When only one side of the U was heated, there was the expected upward flow of heated water in that arm of the tube.
When heat was also applied to the unheated arm, conventional theory predicted that the circulatory flow would slow or stop completely. In practice, the flow actually increased. Provided that there was some asymmetry to the heating, Yarrow's experiment showed that circulation could continue and heating of the cooler downcomer could even increase this flow.
The Yarrow boiler could thus dispense with separate external downcomers. Flow was entirely within the heated watertubes, upwards within those closest to the furnace and downwards through those in the outer rows of the bank.
Later evolution in design
Water drums
The first Yarrow water drums or "troughs" were D-shaped with a flat tubeplate, so as to provide an easy perpendicular mounting for the tubes. The tubeplate was bolted to the trough and could be dismantled for maintenance and tube cleaning.
This D shape is not ideal for a pressure drum though, as pressure will tend to distort it into a more circular section. This flexing led to leakage where the water tubes entered the drum; a problem, termed 'wrapperitis', which was shared with the White-Forster. Experience 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...
s had shown that sharp internal corners inside boilers were also prone to erosion by grooving. Later boilers used a more rounded section, although still asymmetrical rather than fully cylindrical.
Downcomers
The circulation in a Yarrow boiler depended on a temperature difference between the inner and outer tube rows of a bank, and particularly upon the rates of boiling. Whilst this is easy to maintain at low powers, a higher pressure Yarrow boiler will tend to have less temperature difference and thus will have less effective circulation. Some later and higher-pressure boilers were fitted with external downcomers, outside of the heated flue area.
Superheaters
When superheating
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...
was adopted, primarily for use with steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
s after 1900, the first Yarrow boilers placed their superheater coil outside of the main tube bank. Later designs became asymmetrical, with the tube bank on one side doubled and a hairpin-tube superheater placed between them.
Adoption by the Royal Navy
HMS HavockHMS Havock (1893)
HMS Havock was a Havock-class torpedo boat destroyer of the British Royal Navy built by the Yarrow shipyard. She was one of the very first destroyers ordered by the Royal Navy. She had a 240 tons displacement, a speed of 27 knots, and was armed with a single 12-pounder gun, three 6-pounders, and...
, the lead ship of the Havock class destroyer
Havock class destroyer
The Havock class was a class of torpedo boat destroyer of the British Royal Navy. The two ships, and , built in London in 1893 by Yarrow & Company, were the first TBDs to be completed for the Royal Navy, although the equivalent pair from J.I...
s, was built with the then current form of locomotive boiler; its sister ship HMS Hornet
HMS Hornet (1893)
HMS Hornet was a Havock-class torpedo boat destroyer of the British Royal Navy.Built by Yarrow & Company, London, she was laid down in July 1892, launched on 23 December 1893 and completed in July 1894. She served all her service life in Home waters. She served for fifteen years before being sold...
with a Yarrow boiler for comparison. The trials were successful and the Yarrow boiler was adopted for naval service, particularly in small ships. In time the Navy would develop its own Admiralty pattern of three-drum boiler.
Mumford boiler
The Mumford boiler was a variety built by the boilermakers MumfordMumford
Mumford may refer to*Mumford , a 1999 comedy*Mumford, David, a Mathematician*Mumford, Lewis, an American historian*Mumford High School in Detroit, Michigan*Mumford, a hamlet in the town of Wheatland, New York, US...
of Colchester
Colchester
Colchester is an historic town and the largest settlement within the borough of Colchester in Essex, England.At the time of the census in 2001, it had a population of 104,390. However, the population is rapidly increasing, and has been named as one of Britain's fastest growing towns. As the...
, intended for use in smaller boats. The tube banks separated into two groups, with the short tubes slightly curved away from each other. Entry into the lower water drum was perpendicular, requiring an almost rectangular drum with the tubes entering on separate faces. The mechanical weakness of such a shape was acceptable in this small size, but limited the boiler's potential. The casing was small and only enclosed part of the upper steam drum, leading directly to a funnel. A single inverted tee-shaped downcomer linked the drums at the rear of the boiler.
Woolnough boiler
The Woolnough design was used by SentinelSentinel Waggon Works
Sentinel Waggon Works Ltd was a British company based in Shrewsbury, Shropshire that made steam-powered lorries, railway locomotives, and later, diesel engined lorries and locomotives.-Alley & MacLellan, Sentinel Works, Jessie Street Glasgow:...
for their larger railway locomotives. It resembled most other three-drum designs, having almost-straight tubes. Its distinguishing feature was a firebrick wall two-thirds of the way down the furnace. The furnace grate was on the longer side of this, with the combustion gases passing out through the tube bank, along inside a steel outer casing, then back within the shorter tube bank. Coiled tube superheaters were placed in the gas flow outside of the tubes. The combustion gases thus passed through the tube bank twice, once outwards and then again inwards. A single central chimney exhausted from the centre of the far end, not as usual from outside the tubes. The relative temperature difference between gas passage through the two sections of the bank led to a circulation current that was upwards through the first, hotter, part of the bank and downwards through the further, less hot, bank. Circulation was also controlled by an internal weir plate within the upper water drum, so as to keep a depth of water above the ends of the hotter tubes, thus avoiding overheating of dry tubes.
Sentinel used the Woolnough boiler on a number of their larger locomotives, instead of their usual small vertical boiler
Sentinel boiler
The Sentinel boiler was a design of vertical boiler, fitted to the numerous steam waggons built by the Sentinel Waggon Works.The boiler was carefully designed for use in a steam wagon: it was compact, easy to handle whilst driving, and its maintenance features recognised the problems of poor...
. These included railcar
Railcar
A railcar, in British English and Australian English, is a self-propelled railway vehicle designed to transport passengers. The term "railcar" is usually used in reference to a train consisting of a single coach , with a driver's cab at one or both ends. Some railways, e.g., the Great Western...
s for the LNER and LMS
London, Midland and Scottish Railway
The London Midland and Scottish Railway was a British railway company. It was formed on 1 January 1923 under the Railways Act of 1921, which required the grouping of over 120 separate railway companies into just four...
. Sentinel's best-known use of the Woolnough was for the 'Colombian' articulated locomotive
Articulated locomotive
Articulated locomotive usually means a steam locomotive with one or more engine units which can move independent of the main frame. This is done to allow a longer locomotive to negotiate tighter curves...
s. These were a series of four, metre gauge
Metre gauge
Metre gauge refers to narrow gauge railways and tramways with a track gauge of . In some African, American and Asian countries it is the main gauge. In Europe it has been used for local railways in France, Germany, and Belgium, most of which were closed down in mid 20th century. Only in Switzerland...
locomotives of Co-Co wheel arrangement, built in 1934. They ran at the unusually high pressure
High pressure steam locomotive
A high-pressure steam locomotive is a steam locomotive with a boiler that operates at pressures well above what would be considered normal. In the later years of steam, boiler pressures were typically...
of 550 psi and each axle was driven by a separate steam engine, designed by Abner Doble
Abner Doble
Abner Doble , was an American mechanical engineer who built and sold steam-powered automobiles. His father was William Ashton Doble, inventor of the Doble water wheel, and his grandfather and namesake was the founder of the Abner Doble Company.Abner Doble began apprenticing at his family's factory...
. The first was supplied to Belgian Railways, the following three were built for the Société National des Chemins de Fer en Colombe
Rail transport in Colombia
The Colombia railway network has a total length of 3,304 km. There are 150 km of standard gauge connecting Cerrejón coal mines to maritime port of Puerto Bolivar at Bahia de Portete, and 3,154 km of narrow gauge of which 2,611 km are in use...
of Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
, but first shipped to Belgium for testing. Most photographs that exist of these locomotives were taken in Belgium. Little is known of their history after arrival in Colombia.
Admiralty boiler
A later development of the Yarrow was the Admiralty three-drum boiler, developed for the Royal NavyRoyal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
between the First
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
and Second
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
World Wars. Much of the design work was conducted at Admiralty Fuel Experimental Stationinitially the "Admiralty Liquid Fuel Experimentation Station", later the Admiralty Marine Engineering Establishment at Haslar
Haslar
Haslar is place in England, at the southern tip of Alverstoke, on the Gosport peninsula, Hampshire. It takes its name from Anglo-Saxon hæsel-ōra = "hazel - landing place"...
and the first boilers were installed in three of the A class destroyers
A class destroyer
The A class was a flotilla of eight destroyers built for the Royal Navy as part of the 1927 naval programme. A ninth ship, Codrington, was built to an enlarged design to act as the flotilla leader...
of 1927. These boilers established new Royal Navy standard operating conditions for boilers of 300 psi / 600 °F (315.6 °C).
The design was broadly similar to later, high-pressure and oil-fired, versions of the Yarrow. The waterdrums were cylindrical and downcomers were sometimes, but not always, used. The only major difference was in the tube banks. Rather than straight tubes, each tube was mostly straight, but slightly cranked towards their ends. These were installed in two groups within the bank, so that they formed a gap between them within the bank. Superheaters were placed inside this gap and hung by hooks from the steam drum. The advantage of placing the superheaters here was that they increased the temperature differential between the inner and outer tubes of the bank, thus encouraging circulation. In the developed form, the boiler had four rows of tubes on the furnace-side of the superheater and thirteen for the outer-side.
Feedwater
The first boilers suffered problems with both the superheaters and also of poor circulation for the tube rows in the centre of the bank, leading to overheating and tube failure. The circulation problems were addressed by re-arranging the feedwater pipes and by placing baffles inside the steam drum, so as to give a more clearly defined circulation. A circulation augmenter, a steel trough, was placed over the tops of the furnace-side tubes, encouraging a single central upwelling flow to above the water level, encouraging steam bubbles to escape and acting as a steam separatorSteam separator
A Steam separator, sometimes referred to as a moisture separator, is a device for separating water droplets from steam. The simplest type of steam separator is the steam dome on a steam locomotive...
before the water re-circulated down the outer-side tubes. In a manner similar to work taking place around the same time on the LMS railway
London, Midland and Scottish Railway
The London Midland and Scottish Railway was a British railway company. It was formed on 1 January 1923 under the Railways Act of 1921, which required the grouping of over 120 separate railway companies into just four...
and the development of top feed for 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...
s, the feedwater was also routed upwards through 'spray pots' and thus passed through the steam space as droplets. The cold feedwater was thus heated to the same temperature as the boiler water before mixing with it, avoiding disturbance to the circulation path.Although there is no record of any shared development here, between the Royal Navy and the LMS railway
London, Midland and Scottish Railway
The London Midland and Scottish Railway was a British railway company. It was formed on 1 January 1923 under the Railways Act of 1921, which required the grouping of over 120 separate railway companies into just four...
, the two solutions represent an example of parallel evolution
Parallel evolution
Parallel evolution is the development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades.-Parallel vs...
in response to the same problem. As boiler pressure increases, the saturation temperature of wet steam and thus the circulating water increases, making it more sensitive to disruption by cold feedwater.
Superheaters
Initial superheatSuperheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...
performance was disappointing. Superheat at full power was limited deliberately to 100 °F (37.8 °C) so as to avoid reliability problems, which then meant that it was ineffective at low powers. Development work by Babcock & Wilcox resolved this by increasing the steam flow speed through the superheater to 150 ft/sec, avoiding the problems of tube distortion and metallurgical failure. New boilers for the Nelson class battleship
Nelson class battleship
The Nelson class was a class of two battleships of the British Royal Navy, built shortly after, and under the terms of, the Washington Naval Treaty of 1922...
s and the Kent class cruisers could achieve a superheat of 200–250 °F (93.3–121.1 °C) throughout the operating power range at 250 psi.
Backwall
Unlike contemporary American practice, British naval boilers had a large proportion of furnace brickwork, leading to a high temperature within the furnace and consequently a high loading upon the tubes. The use of a water-wall furnace could reduce this.From 1929, Hawthorn Leslie constructed a trial boiler with a partial water-wall to the rear of the furnace. Unlike other water-wall designs, this additional water drum spanned only the centre of the furnace, the vertical tubes were enclosed in a refractory
Refractory
A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...
casing and did not form a closely packed solid wall. The concern was that a full water-wall would unbalance the existing header arrangement of the three-drum boiler, which indeed showed to be the case. Excess steam production at the rear of the steam drum led to disrupted circulation and a problem with priming
Priming
Priming may refer to:* Priming , a process in which the processing of a target stimulus is aided or altered by the presentation of a previously presented stimulus....
. The development of water-walls for this type of boiler was abandoned, although trials did continue with which was trialled with a single water-wall Johnson boiler replacing one of its three three-drum boilers.
Engine 10000
The only large three-drum boiler used in a railway locomotiveSteam 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...
was 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 experimental Engine 10000 of 1924 for the LNER
London and North Eastern Railway
The London and North Eastern Railway was the second-largest of the "Big Four" railway companies created by the Railways Act 1921 in Britain...
company. Having observed the benefits of higher pressures and compound engines in marine practice
Marine steam engine
A marine steam engine is a reciprocating steam engine that is used to power a ship or boat. Steam turbines and diesel engines largely replaced reciprocating steam engines in marine applications during the 20th century, so this article describes the more common types of marine steam engine in use...
, Gresley was keen to experiment with this approach in a railway 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...
. As with the land-based boilers, Harold Yarrow was keen to expand the market for Yarrow's boiler.
The boiler was not the usual Yarrow design, and although designed by Yarrow was built by the Sheffield-based arm of the John Brown
John Brown & Company
John Brown and Company of Clydebank was a pre-eminent Scottish marine engineering and shipbuilding firm, responsible for building many notable and world-famous ships, such as the , the , the , the , the , and the...
shipyard. In operation, particularly its circulation paths, the boiler had more in common with other three-drum designs such as the Woolnough.
Working pressure was of 450 pound per square inches (31 bar) as opposed to the 180 pound per square inches (12 bar) of the contemporary Gresley A1 locomotive
LNER Class A1/A3
The London and North Eastern Railway LNER Gresley Classes A1 and A3 locomotives represented two distinct stages in the history of the British 4-6-2 "Pacific" steam locomotives designed by Nigel Gresley...
s.
The boiler resembled two elongated marine Yarrow boiler
Yarrow boiler
Yarrow boilers are an important class of high-pressure water-tube boilers. They were developed byYarrows and were widely used on ships, particularly warships....
s, placed end to end. Both had the usual Yarrow arrangement of a central large steam drum above two separated water drums, linked by four rows of slightly curved tubes. The upper drum was shared, but the lower water drums were separate. The rearward "firebox" area was wide and spanned the frames
Locomotive frame
A locomotive frame is the structure that forms the backbone of the railway locomotive, giving it strength and supporting the superstructure elements such as a cab, boiler or bodywork. The vast majority of locomotives have had a frame structure of some kind...
, placing the water drums at the limits of the loading gauge
Loading gauge
A loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...
. The forward "boiler" region was narrow-set, with its water drums placed between the frames. Although the outer casings were of similar width, the tube banks for the forward section were much closer. The space outboard of the tubes formed a pair of exhaust flues leading forwards. A large space outside these flue walls but inside the boiler casing was used as an air duct from the air inlet, a crude rectangular slot beneath the smokebox door, which had the effect of both pre-heating the combustion air and also cooling the outer casing to prevent overheating. Longitudinal superheater
Superheater
A superheater is a device used to convert saturated steam or wet steam into dry steam used for power generation or processes. There are three types of superheaters namely: radiant, convection, and separately fired...
tubes were placed in the central space between the steam generating tubes. The third area forwards contained superheater headers, the regulators and the smokebox, but no deliberate heating surface. The external boiler casing remained at much the same width throughout, giving an overall triangular, but curved, appearance. The lower edge of each section stepped upwards, and was obvious externally.
Firing was with coal, at just one end through a conventional locomotive single firedoor, and a single manual fireman. Owing to the single-ended firing and the predominantly longitudinal gasflow, compared to the Yarrow's normal through-bank gasflow, there was a pronounced temperature difference between the front and back of the boiler. This led to the water circulation currents, especially in the second section, to be longitudinal through the water drums, like the Woolnough, rather than the usual Yarrow. The first section, which included some water-tubes to the rear wall, was radiant heated and effectively a water-wall furnace, without any gas flow through the tube bank. Despite this, it still used four rows of tubes. The second section had its gasflow arranged by steel and firebrick baffles so that the combustion gases entered through the centre and passed through the tube banks into the side flues, giving better convective heat transfer.