He chose two 15in diameter outside cylinders but even with only the low expansion ratio of 2:1 that meant the single low-pressure cylinder was a massive 30in in diameter, impossible to fit anywhere else but between the frames . A further 170 4-cylinder compound 0-8-0s (nicknamed 'Swamis' ) and 36 2-8-0s followed, but the 2:1 ratio had been far too low. However, with more cylinders and valve gear, a compound was inevitably more expensive to build and maintain.

Mr. Webb anticipated a 19-20% improvement through compounding but history did not deal his compounds a favourable hand. His successor regarded them as failures and converted compunds back to simples. However, they had been the mainstay of heavy freight haulage for nearly a decade.

Superheating

Of more certain benefit was super heating: a reduction in coal consumption of between 15 and 25% could be measured. Steam was 'saturated' when it left the boiler, but cooling on its way to the cylinders resulted in condensation. If it could be 'superheated' , by passing it through pipes set into the tubes carrying hot fire gases through the boiler, more power could be extracted and no condensation would occur.

In the early years there were no lubricants that would still function at the higher temperatures, and it was the late 1890s before practical, robust superheaters could be fitted. When fitted on the 'G1' and 'G2' Classes the superheaters resulted in economical, powerful and reliable engines, which worked right up to the 1960s.

Enginemen called these engines 'Super Ds' , being a superheated 'D' Class.

Long Boiler

Mr. F.W. Webb introduced 'long boilers' on his 'A' Class 0-8-0s of 1893 in an attempt to create more steam by increasing the length of the tubes, so increasing the heating surface. Modern thought is that it was hardly worth the effort as the tubes at the front, away from the firebox, were never hot enough, and greater length made locomotives more difficult on sharp curves; changing any feature on the railway always impacts something else.

Wheels and Axles

In the early days axles were prone to break, sometimes with disastrous results. The 'Crewe type' with outside cylinders and slide bars firmly mounted in an outside frame was a successful attempt to eliminate cranked axles . The drive could be via a pin on the outside of the wheels, although they were prone to an uncomfortable shuffling movement. Later, as materials got better this problem went away and inside cylinders could be contemplated again.

As long as wheels were sturdy and bearings were large they would meet the unexceptional demands of goods work. Mr. Webb designed robust cast iron wheels with 'H' section spokes and steel tyres for goods work. The steam locomotive was an inherently robust animal as long as care was taken over design and all possibilities of nuts, cotters and pins working loose were eliminated. If it could come loose, it would.