SR U class

Infobox Locomotive
powertype=Steam
name = SR U Class Herring, Peter: "Classic British Steam Locomotives" (Abbeydale Press: London, 2000) Section "U Class" ISBN 1861470576, pp. 120–121]

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caption = Preserved SR U class number 1638 on the Bluebell Railway
designer = Richard Maunsell
builder = SR Ashford Works
builddate = 1928–1931
totalproduction = 50
whytetype = 2-6-0
gauge = RailGauge|ussg
leadingsize = 3 ft 1 in (0.94 m)
driversize = 6 ft (1.83 m)
length = 57 ft 10 in (17.4 m)
weight = 110 tons 14 cwt (112.4 tonnes)
fueltype = coal
fuelc

waterc

cylindercount = 2
cylindersize = 19 in × 28 in (48.26 cm × 71.1 cm)
boilerpressure = 200 lbf/in² (1,378 kPa)
tractiveeffort = 23,866 lbf (106.16 kN)
railroad=London and South Western Railway, Southern Railway (Great Britain), Southern Region of British Railways
locale=Great Britain
railroadclass=4P3F
The SR U Class were 2-6-0 mogul steam locomotives designed by Richard Maunsell for passenger duties on the Southern Railway. They were to be used on cross-country and semi-fast expresses. A highly standardised class of locomotive, the U Class project was given greater emphasis after the Sevenoaks railway accident which involved another class of locomotive, Harry Wainwright's SECR K Class 2-6-4T.

Several members of the class were rebuilds of the K Class at the Ashford railway works, and were soon granted the nickname "U-Boats". Able to operate over most of the Southern Railway network after grouping in 1923, the U Class survived until 1966, when all had been withdrawn from service. Four examples have been preserved.

Background

The U Class was initially intended to be a mogul counterpart to the K Class of 2-6-4T. The design work was already under way in response to the need for an improved version of Maunsell's previous N Class moguls. However the K Class tanks, which were noted for their rough riding on the cheaply-laid rails of the former SECR railway network, had been withdrawn from service after the Sevenoaks rail crash of 1927. The resultant inquiry recommended that the 20 members of the K Class should be rebuilt as 2-6-0 tender locomotives, satisfying an ongoing requirement for a sturdy mixed-traffic locomotive with high route availability on its network.

The design was also intended to replace several elderly classes that were still present in the Southern Railway's fleet, enabling a process of standardisation and ease of maintenance to take place through common components and the capability for mass production.Middlemass, Tom: 'The 'Woolworths' — Woolwich Arsenal's tentative entry into main line locomotive building' ("Backtrack": 4, 148–54)] This had to be married to the ability for the new locomotive to operate over the lightly laid track-work inherited from the former SECR, and as a result, the 2-6-0 wheel arrangement was settled upon.Casserley, H.C.: 'End of the Maunsell moguls—the Southern maids-of-all-work' ("Railway World": 1966, 27), pps. 436–440)]

Construction details

The intended prototype of the U Class was preceded by a rebuilt K Class by three months. The design flaws revealed by the derailment of K Class number A800 "River Cray" at Riverhead near Sevenoaks led to the rapid rebuilding of all K Class engines to the U Class design. This was due to financial expediency, which dictated that Maunsell would rebuild number A805 to the 2-6-0 mogul wheel arrangement at Brighton in 1928, preceding the intended U Class prototype into service. This was considered to be cheaper than constructing a locomotive from scratch, and by the end of 1929 19 K tanks had been rebuilt. This helped to meet the Southern Railway's pressing requirement for a new class of two-cylinder passenger tender locomotives; in due course the entire K Class was rebuilt. The rebuilding involved the removal of the side water tanks, the rear coal bunker and the trailing axles, and the addition of a tender. Reynolds, W.J.: 'The Maunsell moguls' ("S.R. Railway Magazine": 1943, 89), pps. 155–158, 199–202 and 279–282]

The K Class rebuilds visibly differed from the scratch-built locomotives in that they had a lower running plate along the sides of the boiler, necessitating larger wheel splashers to cover the tops of the wheels. They also had N Class-style double spectacle plates rather than the single incorporated on new-build versions. The cabside cutaways were also cut into the roof. Later builds of the class had a flatter top to the dome covers than those seen on the K Class rebuilds. Ex-K Class locomotive A890 was rebuilt once again as the prototype of Maunsell's newer U1 Class three-cylinder derivative in 1928.

The prototype U Class that had been built from scratch emerged from Ashford in June 1928. The U Class as originally designed had tapered chimneys and smokebox snifting valves, once again a feature seen on the N Class. These were later removed and new chimneys of the U1 pattern fitted. Smoke deflectors were fitted from 1933, as with most of the locomotives designed by Maunsell. Thirty members of the class were constructed as per Maunsell's original design.

Two designs of Maunsell tender were used, one of which was of the same convert|4000|impgal|l|adj=on|sigfig=5 design as used on the N Class, with the raves preventing the loss of coal through spillage sloped inwards.Clarke, Jeremy: 'The Locomotives of R. E. L. Maunsell, Part 4: The 'Mogul' Family–SR' ("Steam World": 249 (March 2008), pp. 54–55] The use of a tender common to the N Class enabled the further standardisation of components between the two classes. The other tender design was of convert|3500|impgal|l|sigfig=5 capacity, and was straight-sided. A total of 50 engines was constructed, alternating between Ashford and Brighton works.

Operational details and preservation

The U Class was a reliable and economical design, and proved to be more than capable of attaining speeds in excess of convert|70|mph|abbr=on. Their high route availability saw them distributed more widely than their N Class counterparts, which meant that they were especially useful on Western Section trains between Salisbury and Exeter. Their "go anywhere" nature earned them the nickname of "U-Boats". Crews praised their abilities to achieve what they were designed to do, though they represent one of the rather more unglamorous classes of mixed-traffic passenger locomotive.

Several trials were made by the Southern Railway operating department to improve efficiency across their locomotive fleet. U Class number A629 was fitted with an experimental pulverised fuel burner of German design, which proved unsuccessful. The decision to end the experiment was made on safety considerations, as powdered coal is potentially explosive.

Before nationalisation the class provided an ideal test-bed in response to a government-backed scheme concerning locomotive fuel arrangements in 1948. Two of the class, numbers 1625 and 1797, were converted to oil burners. Several other members of the class were designated for conversion, but the project was abandoned before this could take place. From 1955 23 members of the class received new chimneys of the BR Standard Class 4 variety and replacement cylinders, which had become worn out through intensive use. Withdrawals began in 1962, and all were struck off the locomotive register by 1966, although four have survived. The survivors are (3)1618 and (3)1638, based on the Bluebell Railway, and (3)1806 and (3)1625, based on the Mid-Hants Railway. (3)1806 is the only survivor of the K Class rebuilds.

Livery and numbering

Southern Railway

The entire class, from construction in 1928, was finished in Maunsell lined Southern Railway Olive Green with yellow markings and "Southern" on the tender. During the Second World War, the U Class was released in wartime black livery with Oliver Bulleid's Sunshine Yellow lettering. The class was initially numbered in the Southern's post-grouping parlance from A790 to A809 for the K Class rebuilds, and A610 to A639 with the as-built batch. This was subsequently changed to 1790–1809, and 1610–1639 respectively during the 1930s.

Post-1948 (nationalisation)

The entire class was absorbed by British Railways (BR) in 1948, and was given the BR Power classification 4P3F. Longworth, Hugh: "British Railway Steam Locomotives: 1948–1968" (Oxford Publishing Company: Oxford, 2005) ISBN 0860935930] Livery was initially as Southern Railway, though with "British Railways" on the tender, and an "S" prefix to the Southern number. This was succeeded by the BR mixed traffic lined black livery with red and white lining, and the BR crest on the tender. Numbering was in line with the BR standard numbering system, in the series 31790–31809 for the K Class rebuilds, and 31610–31639 for the rest. [Ian Allan ABC of British Railways Locomotives, winter 1958–59 edition]

References

External links

* [http://www.semgonline.com/steam/uclass_1.html Maunsell U class 2-6-0]
* [http://www.railuk.co.uk/steam/getsteamclass.php?item=U Steam Loco Class Class U Details]
* http://www.bluebell-railway.co.uk/bluebell/loco_static.html#u
* http://www.bluebell-railway.co.uk/bluebell/loco_operational.html#1638