GWR 3031 Achilles Class – Dean Single – Locomotive Profile

GWR_Dean_single_4-2-2_3050_Royal_Sovereign_(Howden,_Boys'_Book_of_Locomotives,_1907)

A newly built 3050 Royal Sovereign
Photo source: Wikipedia
 The Dean Single was a passenger steam locomotive built by the Great Western Railway between 1891 and 1899 under the direction of GWR’s chief mechanical engineer William Dean.  The locomotive class was known by many different names such as 3031 Class or Achilles class, both named after the first locomotive of the class built but the name “Dean Single” was the one most used, due to the confusing evolution of the class. In total 80 members of the class were built over several batches and rebuilds. The first 30 members of the class were built as 2-2-2s of the 3001 class. The first eight were actually convertible broad gauge locomotives but were modified to standard only gauge in the 1892, when broad gauge was removed by the Great Western Railway. A further 22 of the 3001 class were built between 1891 and 1892 but these were standard gauge and not convertible to broad gauge.

800px-GWR_Dean_single_2-2-2_3009_Flying_Dutchman_(Howden,_Boys'_Book_of_Locomotives,_1907)No. 3009 Flying Dutchman in 3001 class form

Photo source: Wikipedia


However there were problems due to the HUGE 7ft 8in driving wheels. Despite the fact that the 3001 class were fitted with the largest boiler ever fitted to a GWR 2-2-2 locomotive the boiler was constrained because it had to fit between the huge driving wheels. On most locomotives this problem wouldn’t have happened as the driving wheels are usually smaller and so their height does not affect the boiler and its workings. This meant when the boiler capacity was increased it could only been done by making the boiler longer and not wider. As a result what happened was the smokebox and cylinders were now in front of the leading axle. This meant trouble as the extra weight of the larger wheels put extra stress on the leading axle and made locomotives unstable especially at speed. Disaster happened on 16 September 1893 Great Western locomotive number 3021 Wigmore Castle was hauling an express train, when it derailed in Box Tunnel when the front axle broke. The cause of the accident was thought to be excessive weight being carried on the front axle, so it was decided to replace the leading pair of wheels in the 3001 class with a bogie. The is in turn created more problems because of the steam chest on the 3001 class which was located underneath the cylinders and contained two slide valves. The inverted placement of the valves allowed them to drop away from the face of the steam ports when steam was shut off, thus reducing wear. A conventional bogie design would of obstructed access to the steam port faces so William Dean instead used a suspension bogie which was unique at the time.

278f524cMy Dean Single Model

The Dean Single I know and love first appeared when 3021 Wigmore Castle the box tunnel victim was rebuilt as a  4-2-2 in March 1894 with the other members of the class being rebuilt between June and December 1894. The second batch of the Dean Singles were built at Swindon works between March 1894 and March 1899. Due to the huge changes in the design from the 3001 class the new locomotives and rebuilds were reclassified as 3031 Achilles class, named after the first locomotive of the new batch of singles.

These new locomotives differed from the rebuilds in having their cylinder diameter reduced from 20 inches to 19 inches, and the springs for the trailing wheels located above the footplate and outside the cab, necessitating a reduced width for the latter. The evolution of the Dean Single didnt stop here as from 1898 their driving wheels were increased by half an inch to 7ft 9in when they were fitted with thicker tyres.

Famous members of the class

3015 Kennet was involved in the 1900 Slough rail accident

3021 Wigmore Castle crashed in Box tunnel in 1893.

3041 The Queen, originally named James Mason, was an example of this class allocated to Royal Train duties. A replica was built in the 1980s and currently lives at Windsor station.

3065 Duke of Connaught made a record-breaking run with the Ocean Mail on 9 May 1904, covering the distance from Plymouth to Paddington in 227 minutes.

3046 Lord of the Isles has enjoyed a certain amount of celebrity, having been chosen as the prototype for a Tri-ang model locomotive. Since then the engine has also been modelled by Brio and Matchbox.

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