du Temple boiler The
du Temple was an early naval
water-tube boiler, patented in 1876. It was invented by
Félix du Temple in France and was 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. 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 and especially numerous, a total of 3,744 being used in some boilers. White–Forster boilers were introduced into the Royal Navy from 1906, for
light cruisers and
torpedo boat destroyers. 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 perpendicularly, 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 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.
Reed boiler The Reed boiler was used by
Palmers of
Jarrow. It was similar to the Normand, with downcomers and curved tubes that entered cylindrical drums perpendicularly.
Thornycroft boiler The
Thornycroft 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.
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 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. A vertical U-shaped tube was arranged so that it could be heated by a series of
Bunsen burners 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.
Superheaters When
superheating was adopted, primarily for use with
steam turbines after 1900, the first Yarrow boilers placed their superheater coil outside 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 Havock, the lead ship of the
Havock class destroyers, 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.
Mumford boiler The
Mumford boiler was a variety built by the boilermakers Mumford 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.
Woolnough boiler The
Woolnough design was used by
Sentinel 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 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
railcars for the
LNER and
LMS. Sentinel's best-known use of the Woolnough was for the 'Colombian'
articulated locomotives. 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 and each axle was driven by a separate
steam motor, 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.
Admiralty boiler A later development of the Yarrow was the
Admiralty three-drum boiler, developed for the
Royal Navy between the
First and
Second World Wars. Much of the design work was conducted at
Admiralty Fuel Experimental Station 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 (2.0 MPa) / . 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. 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. 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. In operation, particularly its circulation paths, the boiler had more in common with other three-drum designs such as the
Woolnough. It has also been described as an evolution of the
Brotan-Deffner water-tube firebox, with the firebox extended to become the entire boiler. Working pressure was of as opposed to the of the contemporary Gresley
A1 locomotives. The boiler resembled two elongated marine
Yarrow boilers, 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 of 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. == References ==