Eagle, 25-March-1955

An Opportunity Arises

In the early 1950s Robert Riddles was the British Railways (BR) Executive for Mechanical and Electrical Engineering and he was responsible for the introduction of a range of simple, two cylinder standardised steam locomotives intended to be in service until the 1970’s. These locomotives became know as BR Standards and 998 locomotives within 11 different classes were built between 1951 and 1960. The Duke  took the number of classes to 12 and total BR Standards built to 999.

The first BR Standard class of locomotive to be built were 4-6-2 Class 7MT (Mixed Traffic) which filled the British loading gauge i.e. built to maximum height and width. There was no need for a new range of express passenger locomotives (Class 8P) as the private railway companies, which had been nationalised in 1947, had left the newly formed British Railways well provided for. However, an unfortunate accident at Harrow in 1952 resulted in the scrapping of one of the ex-LMS Pacific class locomotives, which thus presented Riddles with an opportunity to design a prototype for the future.

Designing The Duke

The Duke was designed at Derby locomotive works in 1953 and was constructed at Crewe locomotive works in 1954. After approximately eight years’ service during which the locomotive enjoyed, at best, a mixed reputation on the main line, it was withdrawn and sent for scrap.

That bald story, although correct, gives no clue as to what makes The Duke unique and why it holds such a special place in the history of steam locomotive development in Great Britain. “Unique” is a much overused word in connection with many artefacts, but this particular locomotive probably better earns that epithet than any other.

The table along side this text compares The Duke with the Britannia Class. There are only a few differences but chief amongst them is the valve gear.

The DukeBritannia
Wheel Configuration 4-6-2 (Pacific)4-6-2 (Pacific)
UIC Cclassification 2′C1′h32′C1′h2
Gauge 4 ft 8 1⁄2 in (1435 mm)4 ft 8 1⁄2 in (1435 mm)
Leading Wheel Diameter 3 ft 0 in (0.914 m)3 ft 0 in (0.914 m)
Driver Diameter 6 ft 2 in (1.880 m)6 ft 2 in (1.880 m)
Trailing Wheel Diameter 3 ft 3 1⁄2 in (1.003 m)3 ft 3 1⁄2 in (1.003 m)
Length 67 ft 8 in (20.62 m)68 ft 9 in (20.96 m)
Width
9 ft 0 in (2.74 m)8 ft 8 3⁄4 in (2.66 m)
Height 13 ft 0 1⁄2 in (3.98 m)13 ft 0 1⁄2 in (3.98 m)
Axle Load 22.00 long tons (22.35 t)20.50 long tons (20.83 t)
Weight on Driver Wheels 66.00 long tons (67.06 t)61.50 long tons (62.49 t)
Locomotive Weight 101.25 long tons (102.87 t)94.00 long tons (95.51 t)
Tender Weight BR1E: 55.50 long tons (56.39 t)
49.15 long tons (49.94 t)
BR1J: 53.70 long tons (54.56 t)
Tender Type 1954–1958: BR1E
BR1
1958–1962: BR1J
Fuel TypeCoalCoal
Fuel Capacity 10 long tons (10 t)7.0 long tons (7.1 t)
Water Capacity BR1E: 4725 imp gal (21480 l; 5674 US gal)
4,250 imp gal (19,300 l; 5,100 US gal)
BR1J: 4325 imp gal (19660 l; 5194 US gal)
Boiler BR13BR1
Boiler Pressure250 psi (1.72 MPa)250 psi (1.72 MPa)
Firegrate Area Heating Surface48.6 sq ft (4.52 m2)42 sq ft (3.9 m2)
Tubes and Flues 2264 sq ft (210.3 m2)2,264 sq ft (210.3 m2)
Firebox 226 sq ft (21.0 m2)210 sq ft (20 m2)
Superheater Area 677 sq ft (62.9 m2)718 sq ft (66.7 m2)
Number of Cylinders Three, two outside + one insideTwo, outside
Cylinder Size 18 in × 28 in (457 mm × 711 mm)20 in × 28 in (508 mm × 711 mm)
Valve GearCaprottiWalschaerts
Chimney TypeDoubleSingle

Caprotti Valve Gear

Caprotti rotary valve gear had, in the years immediately after World War Two, been brought to a state of much improved efficiency by the British company Associated Locomotive Equipment and indeed had been successfully fitted to several LMS Black 5 locomotives built after WW2 the last 2 numbers 44686 and 44687 were constructed by British Railways at Horwich Works as late as 1951. Interestingly, they were also fitted with raised running plates without splashers, a double chimney and SKF roller bearings on all axles – something of a forerunner to the BR Standards.

Caprotti valve gear had previously been fitted to a batch of twenty Black Fives, nos. 44738-57, built in 1948. The valve gear on these was driven by one drive-line between the frames, driven from the leading coupled axle. Although these locomotives developed a great deal of power at high speeds and were free in coasting, acceleration at low speeds was poor. 44686 and 44687 were fitted with a modified form of valve gear, with an external shaft on each side, driven by a worm gear mounted on a flycrank attached to the driving axle.

Thus with these principles laid down, Derby drawing office set to work on the detailed design of a Class 8P, once Riddles had received approval for his plan from the British Railways Board. They indicated that what they envisaged was an enlarged Britannia Class Pacific, using as many common parts as possible, and essentially that is what Riddles delivered. Although Derby was responsible for the main design work, Swindon drawing office was asked to design the exhaust system.

The representative from the Associated Locomotive Equipment Company, Mr Tom Daniels, had enjoyed close contact with the noted French steam locomotive engineer Andre Chapelon, as a result of which the company was the agent for the patented Kylala-Chapelon double blastpipe exhaust system. Tom Daniels felt that this Kylchap system was what was needed for optimum draughting in conjunction with the rotary Caprotti valve gear. However, possibly in the light of patent costs, this advice was ignored and Swindon produced a plain, bifurcated, blastpipe with double chimney. It has been suggested that the dimensions were simply a double version of that found on the Great Western Dean goods locomotive and, perhaps not surprisingly, Tom Daniels was disappointed at this outcome. The Duke was built with the Swindon designed double blastpipe and chimney.

Riddles (an ex-LMS man) elected to fit his prototype Class 8 with British Caprotti rotary valve gear and, moreover, to fit his prototype with three cylinders. Riddles himself said, some years later, that the opportunity to build a “one-off” with Caprotti valve gear, eliminating or overcoming all the faults of reciprocating valve gear, giving constant valve openings at all times coupled with free exhaust, was too good a chance to miss.

The Duke Appears

The livery of The Duke was a continuation of the BR standard practice. The Class was given the power classification 8P. Following on from the Britannias, The Duke was numbered under the BR standard numbering system in the 71xxx series with The Duke being given the number 71000 and nameplates having a black background, located on the smoke deflectors.

The locomotive was outshopped from Crewe Works on Saturday, 22 May 1954 and was named Duke of Gloucester prior to entering revenue-earning service. Had further locomotives been constructed, they would have belonged to the Duke Class, standing alongside the sister locomotives of the Britannia and Clan Classes.

The Duke was allocated to Crewe North Motive Power Depot code 5A.