The LNER Encyclopedia

After realising that his 11B (LNER D9) locomotives were too small for the Great Central Railway's (GCR) growing requirements, Robinson built his B1 4-6-0 and C4 4-4-2 locomotives as a comparative test. The C4 proved successful and was built in larger numbers. When further engines were required, Robinson reverted back to the 4-6-0 design with his B2 'Sir Sam Fay' locomotives. Although the 'Sir Sam Fay' locomotives looked powerful, the design was a disappointment and Robinson quickly produced his Class 11E 'Director' design (LNER D10). The 4-4-0 design allowed a larger space for the firebox between the driving axles (10ft) compared to the rear axles of the B2 (8ft 3in). The D10's firebox had a steep back so that it extended over the rear axle slightly. With a shorter boiler and smaller diameter cylinders (20in), the new D10 design represented a good balance between steam generating capacity, and ability to use this steam.
The D10s were built with 10in diameter piston valves with the unusual feature of outside admission. The exact reason for this unknown, but it could have been a combination of economy, and the need for a quick replacement for the B2s.
A total of ten D10s were built in 1913, and quickly proved to be a great success. A second order was place in 1916, but this was postponed until after World War 1. When the order was re-issued in 1919 it included a number of alterations. The alterations were deemed sufficient for a new class, and they became the Class 11F (LNER D11) 'Improved Directors'.

First part of this collection features 4 locomotives in Great Central Livery
https://railway-photography.smugmug.com ... /i-3mt3r9W

Neil

I have added the rest of the photos of the Robinson Class D10 (GCR Class 11E) 'Directors' 4-4-0 Locomotives
Featuring LNER numbered locos
https://railway-photography.smugmug.com ... /i-P7XMXSw
and B.R. numbered locos
https://railway-photography.smugmug.com ... /i-jkwww9J

Neil

The Directors' outside admission PVs were not particularly unusual at the time they were built, and they were used elsewhere - they were the norm on the NER for instance. Slide valves, pressed against the valve-chest face by steam pressure, inevitably had outside admission, and if PVs were driven in the same way they inherited this. The arrangement had the disadvantage of putting live-steam pressure on the valve-spindle packings, and the Improved Directors were given what was effectively the valve-gear of the inside cylinders of the Faringdons, whose PVs were driven through rocking levers to give inside admission, and could be set parallel to the cylinders.

Outside admission did give a direct path for exhaust steam and it was Bulleid's choice for his Pacifics.