Double chimney
A double chimney (or double stack, double smokestack in American English) is a form of chimney for a steam locomotive, where the conventional single opening is duplicated, together with the blastpipe beneath it. Although the internal openings form two circles, the outside appearance usually forms a single elongated oval.
Purpose
The classic exhaust design for a steam locomotive began with Hackworth's invention of the blastpipe, placed centrally within a tall chimney. Victorian developments reduced the chimney's height, such that natural draught was no longer significant. The standard design was then a circular drumhead smokebox, with a single blastpipe nozzle leading into a chimney with a flared petticoat pipe beneath it. From the work of theorists such as W.F.M. Goss of Purdue University, and later S.O. Ell of Swindon,[1] guidelines were developed at each locomotive works, describing how these were to be proportioned.[2]
It was recognised both that a particular diameter of chimney and blastpipe would be needed for the steam-raising capacity of each boiler, and also that the conical taper from blastpipe to chimney could not be made too steep. As boilers became more powerful, not only did the chimney diameter need to become greater, but also the minimum height for the chimney was becoming longer – just as the increasing size of boilers restricted the clearance height available within the loading gauge. A chimney height[i] of at least 24 inches was considered the minimum workable.[1] By the 1930s, it was increasingly difficult to provide such a height and other solutions were sought.
A solution to this limit was to adopt a double chimney. This allowed adequate cross-section area for airflow, whilst reducing the diameter of each and thus the minimum height needed for an acceptably gentle taper.[3][ii]
Kylchap blastpipes
A simultaneous development was the
Although there is no reason why one approach, either the double chimney or the Kylchap blastpipe, depends on the other, interest in both was generally simultaneous and so both were often installed together.
Disadvantages
The first 50 of the Ivatt class 4MT 2-6-0 were built with double chimneys. These performed poorly however, and were noted as poor steamers. Work on the static test plant at Rugby discovered that there was both no advantage to the double chimney and also that it had been poorly designed initially. When revised with a single chimney and improved gasflow in the smokebox, their steaming rate was raised from 9,000 lb/hour with a double chimney to 17,000 lb/hour with a single chimney, even though this was still below the theoretical limit, restricted by firegrate size, of 19,000 lb/hour.[4]
A minor disadvantage could be a 'softer' exhaust blast for the purpose of lifting the external smoke clear of the driver's vision. When the LNER A3 class were fitted with double chimneys in the late 1950s, they suffered problems with smoke obscuring the view from the cab.[iii] The solution to this was to fit small Witte-type smoke deflectors of the German pattern.
Notable installations
Many double chimney installations, at least in the UK, were performed as experimental conversions in the 1930s, rather than as new builds.
LNER A4
The first of the A4 class reverted to a single chimney and a conventional blastpipe. They had the greatest attention paid to their gas flow generally, both the inlet and exhaust sides. With the P2s, there had been a tendency for an excess of draught, when working hard at a long cut-off, enough to lift the fire. To avoid this, the A4s used a 'jumper top' on their blastpipe, a loose ring which rose under the influence of a strong blast jet, increasing the effective nozzle diameter and so reducing the drawing effect of the blast. This device could not be applied to either a double chimney, nor to a Kylala blastpipe, but it is not clear if that was the only reason for the simplified single blastpipe.[6]
Peppercorn's A2 pacifics were built, post-war, with similar double Kylchap blastpipes.
LMS Jubilee
Five members of the LMS Jubilee class were experimentally fitted with double chimneys at different times. The first was 5684 Jutland, a double chimney with Kylchap petticoats in 1937.[9] This improved both the steaming capacity and also reduced coal consumption, although it was removed after a year owing to problems with the excessive draught causing spark-throwing from the chimney and a build-up of excess smokebox ash.[10] 5742 Connaught and 5553 Canada were then fitted with plain double chimneys in 1940, which was removed from Canada after a short time, but which Connaught carried until 1955.[9]
As part of experiments at Rugby test plant, 45722 Defence was fitted with a double chimney from 1956 to 1957.[11] In 1961 a double exhaust was fitted to 45596 Bahamas which carried it through withdrawal and into preservation.[11] Two further engines, 5735 Comet and 5736 Phoenix were rebuilt with a 2A taper boiler and double chimney in 1942.[12] They were to have been a prototype for the rebuilding of the entire class but, in the end, the only Jubilees so to be treated. All the Royal Scot class were rebuilt along similar lines as were many of the Fowler Patriot locos.
LMS Black 5
Some of the first BR-built Black 5s were built with
A second batch of two more Caprotti-fitted engines was tried in 1951,
Great Western King class
In September 1955, GWR King class 6015 King Richard III was fitted with a double chimney for trials. These were successful and so the whole class was refitted with them. Some of the Castle class were similarly refitted. Tests with a dynamometer car in hauling the Cornish Riviera in 1956 did not show an evident increase in performance, but did show an 8% improvement in the efficiency of coal consumption. Water consumption remained constant, indicating that this was an improvement in combustion and heat transfer, rather than the reduction in engine exhaust back pressure, indicated by some other tests.[17]
British Railways Standard classes
The BR Standards had been designed from the outset with their draughting based on the earlier work of S.O. Ell. Despite this, some of the classes steamed poorly, notably the Class 4 4-6-0. In 1957, 75029 was successfully fitted with a double chimney, leading to its adoption across many of the class.[18]
At the same time, there was also a proposal to test a Giesl ejector on the 9F[vii] Possibly as a comparison for this, 92178 was built with a double chimney. The double chimney was so successful[20] that it was adopted as standard for all 9F built from 92183 onwards,[viii] including the three fitted with a mechanical stoker.[22]
Duke of Gloucester
The
In service, Duke of Gloucester performed infamously poorly, with a reputation for poor steaming. It had a short service life, as a combination of both the rapid withdrawal of steam traction on British Rail and also its poor performance and a reluctance to expend effort in solving this.[23][25]
Duke of Gloucester was rescued from
United States
Union Pacific Railroad
Several late steam era designs on the
Other Union Pacific designs to get double stacks were the late-era articulated locomotives built for the railroad, including the final group of 1942 built Union Pacific Challenger locomotives and the entire run of Union Pacific Big Boy locomotives.[29] While some Challenger and Big Boy locomotives were equipped with smoke deflectors, smoke was not as problematic on them as it was on the FEF class due to their much longer boilers. A handful of the double chimney equipped Challengers were diverted to the Denver and Rio Grande Western Railroad, from which they would later serve on the Clinchfield Railroad. The operational locomotives of the modern Union Pacific Steam Program, UP 844, UP 4014 and the now retired UP 3985 all retained their double chimneys.
Pennsylvania Railroad
Double stacks were a common feature on several of the PRR's duplex locomotive classes and other experimental designs in the late steam era. Pennsylvania Railroad class S1 a lone prototype 6-4-4-6 used a double stack as well as the Pennsylvania Railroad class Q2 a 4-4-6-4 duplexs which had a total of 26 locomotives built. The Pennsylvania Railroad class T1 a duplex class with 52 locomotives produced also carried double stacks.Pennsylvania Railroad class S2 used a unique quadruple stack system as part of its experimental steam turbine design. This one off engine introduced in 1944 was scrapped by 1952.
Pennsylvania Railroad 5550 a new build based on the T1 class is currently underway being built by the T1 Steam Locomotive Trust. As of 2021, the engine's boiler is being constructed and when complete will contain a double stack like the original locomotives.[30]
Southern Pacific Railroad
Several of the Southern Pacific Railroad's larger engines such as the Southern Pacific class AC-9 and the Southern Pacific class AC-12 all used double stack systems. These were also equipped with "stack splitters" a design feature going back to Southern Pacific's single stack Mallet's that reduced the speed of the exhaust to prevent damaging the roofs of snow sheds.[31] Several of these engines were built with a Cab forward 4-8-8-2 design, placing the locomotive cab on the forward part of the engine to prevent asphyxiation during long tunnel and snow shed segments on the Southern Pacific.[32] Southern Pacific 4294 the only survivor of Southern Pacific's cab forward locomotives is preserved in Sacramento, California at the California State Railroad Museum.
South America
L.D.Porta's Argentina
South Africa
South African Class 26 4-8-4
Following on L.D. Porta's design methodology, the South African Class 26 4-8-4 L.D. Porta (better known via its nickname Red Devil) was equipped with a double chimney system outfitted with Lempor ejectors along with a Gas Producer Combustion System to improve efficiency.[35]
Notes
- ^ Note that this is the internal length of the chimney, to the petticoat pipe, not the external height above the boiler.
- ^ A similar approach led to the Giesl ejector. This used a large number of separate chimney channels, arranged in a row, allowing each to become a very long, thin taper.
- ^ The A3s did not have the smoke-lifting streamlining of the A4s.
- ^ i.e. 4472 Flying Scotsman
- ^ It was a perennial problem for the design of poppet valves to not leave excessive 'dead' space around them.
- ^ The variable lead of the Stephenson link valvegear gave a long lead when notched up to a short cutoff and was known to climb hills well but not to run so well at speed
- ^ Fitted to 9F 92250, later converted to a double chimney.[19]
- ^ The double chimney 9Fs were 92165–92167 (stoker-fitted, as built), 92178 (first experiment), 92183–92250 (as built) and 92000–92002, 92005, 92006 (modified) [21]
References
- ^ a b Walford & Harrison (2008), p. 29.
- ^ Semmens & Goldfinch (2003), pp. 73–74.
- ^ Walford & Harrison (2008), pp. 28–29.
- ^ Semmens & Goldfinch (2003), p. 74.
- ^ Nock (1982), pp. 140–142.
- ^ Nock (1982), pp. 146–147.
- ^ a b Semmens & Goldfinch (2003), p. 78.
- ^ Nock (1966), pp. 261–262, Chapter 20: Finale.
- ^ a b Rowledge & Reed (1984), p. 31.
- ^ Haresnape (1970), p. 34.
- ^ a b Rowledge & Reed (1984), pp. 38–40.
- ^ Rowledge & Reed (1984), p. 45.
- ^ Nock (1966), pp. 181–182, Chapter 14: Post-War Development.
- ^ a b Clay (1972), p. 47.
- ^ Clay (1972), pp. 46–47.
- ^ Clay (1972), p. 48.
- ^ Nock (1966), pp. 265–269, Chapter 20: Finale.
- ^ Walford & Harrison (2008), pp. 29, 214.
- ^ Walford & Harrison (2008), pp. 33–37.
- ^ Walford & Harrison (2008), pp. 212–215.
- ^ Walford & Harrison (2008), p. 28.
- ^ Walford & Harrison (2008), pp. 28–30, 36.
- ^ a b Herring (2000), pp. 188–189, Standard Class 8.
- ^ Nock (1966), pp. 228–229, Chapter 17: The British Standard Locomotives.
- ^ a b c d "Modifications". 71000 Duke Of Gloucester.
- ^ Don Strack (26 December 2019). "Smoke Lifters on Union Pacific Steam Locomotives". Utah Rails.
- ^ "OP-16553". digital.denverlibrary.org. Retrieved 2021-12-30.
- ^ "Big Boy Steam - Holy Brake Smokes & Double-Headed Big Boys!", Facebook, retrieved 2021-12-30
- ^ Richard F. Cole (May–June 1975). "Union Pacific's Articulateds". Western Prototype Modeler – via Utah Rails.
- better source needed]
- ^ "Southern Pacific 4-8-8-2 "Cab Forward" Locomotives in the USA".
- ^ ""Cab Forward" Steam Locomotives".
- ^ Martyn Bane. "Argentina".
- ^ Martyn Bane. "Third Generation Steam for North America – A 6000hp Triple Expansion Compound 2-10-0".
- ^ "Gas Producer Combustion System (GPCS)". Trainweb / The Ultimate Steam Page.
Sources
- Clay, John F. (1972). The Stanier Black Fives. ISBN 07110-0274-6.
- Haresnape, Brian (1970). "Class 5XP 4-6-0 Jubilee". Stanier Locomotives. Ian Allan. ISBN 0-7110-0108-1.
- Herring, Peter (2000). Classic British Steam Locomotives. Standard Class 9. ISBN 1-86147-057-6.
- Nock, O. S. (1966). The British Steam Railway Locomotive. Vol. II, from 1925 to 1965. Ian Allan.
- ISBN 0-7153-8388-4.
- Rowledge, J.W.P.; Reed, Brian (1984) [1977]. The Stanier 4-6-0s of the LMS. Newton Abbot: ISBN 0-7153-7385-4.
- Semmens, P.W.B.; Goldfinch, A.J. (2003) [2000]. How Steam Locomotives Really Work. Oxford: ISBN 978-0-19-860782-3.
- Walford, John; Harrison, Paul (2008). The 9F 2-10-0 Class. A detailed history of British Railways Standard Steam Locomotives. Vol. 4. Bristol: ISBN 978-0-901115-95-9.
Further reading
- Bell, Arthur Morton(1936). Locomotives. their construction, maintenance and operation (3rd ed.). London: Virtue.
- Cook, A.F. (2000). Raising Steam on the LMS: The Evolution of LMS Locomotive Boilers. RCTS. ISBN 978-0901115850.
- Holcroft, H. (1957). Great Western Locomotive Practice 1837–1947. Locomotive Publishing.
- Koopmans, J. J. G. (2014). The Fire Burns Much Better ... Camden Miniature Steam Services. ISBN 978-1909358058.