I was once asked 'What do you think characterises an English made Locomotive?" and I had to say it was the cylinders and frames that did it for me! English designers have always liked internal cylinders and internal frames -thus all you would see externally would be the wheels and conrods. A classic example of the English style would be the GCR 'Butler Henderson' only if you climbed into the gap between the frames would see any of the motions...

Cylinders

By and large most steam locomotives are of the 'simple expansion' type. The other method of using steam is called 'compounding' in which the used steam (still with heat energy in it) is used again (and sometimes a third time). In a simple expansion type the steam is used by the cylinders and then blasted out of the blast pipe under the smoke stack. In a compound engine the steam goes from the cylinder into a receiver vessel and thence to the second set of cylinders to be used a second time and thence to the blast pipe. To start a compound engine live steam from the boiler is admitted to the receiver vessel to 'prime' the secondary system. In some French designs (notably NORD) there was a system of running the locomotive in one of five manners depending on what sort of working was required....

It was found that a vessel that was TWICE the volume of the HP cylinder was the best for performance of the LP cylinder -thus the popularity of von Borres 3 cylinder compounds in which 1 cylinder was HP and 2 LP. The other way around was only practiced by the LNWR under Webb. The practice of having 1 HP cylinder and 1 LP cylinder was more popular on French and German made locos than English -although the NER did have a few designed by Sir Vincent Raven.

Update:

I have since found out that at least 2 NORD de Glehn type compounds found their way to the american PRR along with 1 Webb compound. The British govt forbade the LNWR from selling to the americans so Messrs Beyer Peacock made one for export. (It was not liked).

Other designers have tried to make their mark with compounding. The Vauclain system had the HP and LP cylinders mounted on top of each other and both cylinders acted on the same wheel. The other notable system was used by Johnestone. This had co-axial cylinders i.e. the HP cylinder was in the centre of the LP cylinder.

Plumbing

For reasons I have yet to discover one of the easiest ways of looking at a mystery photo of a loco and trying to decide where and when it was made -is to to look at the plumbing. As a guide, most English locos are devoid of external plumbing -with the exception of 'The Standards' designed by Riddle, (who used a very heavy US influence in the 9F especially). You may find such things as steam heating pipes and brake hoses -but bar the hand rails on an English Loco that is it... If you were to look at a typical German loco of the 1900's you would find sand boxes with delivery pipes, Westinghouse pumps, air tanks and pipes seemingly just bolted on ad hoc. I have a picture of a Royal Saxony Meyer loco in which the top of the loco is piled so high with clutter that I doubt the driver could even see the end of the loco -let alone the signals...

The Westinghouse Air pump is perhaps one of the most easily missed pieces in modelling and even then -people get it wrong. The pump uses steam to compress the air. This means that the vanes are at the TOP of the pump to cool the air compressor side of the pump -and normally in position to get a goodly draught as the loco moves. On German made locos the air tanks are normally on top of the water tanks, with the pump on the LEFT side of the loco. Oh, don't put a Westinghouse pump on a european loco made before 1880 -unless it is a retro fit!

American locos seem almost to be buried under their plumbing. Stylistically the design of a typical US loco will have exposed steam, sand, water, and air plumbing with no attempt to disguise what it is. This made for easier maintaining in low tech outposts -not all US stations had skilled fitters. Most US railways bought their locos from supply companies (Baldwins, Lima -etc) rather than manufacture them themselves, although there were some very notable exceptions, such as 'The Norfolk and Western'. This may have lead to more utilitarian style than grace...

The ultimate in US style plumbing can only really be seen on a Challenger locomotive. It doesn't look like a locomotive, rather more like some form of chemical works that moves. I am a great admirer of this locomotive and consider it to be the epitomy of US steam power and design philosophy

Frames

English designers also liked plate frames -rather than the bar frames that are classicly US, French, or German. This does make a UK designed loco far easier to model than say a Henshel und Sohn design. Most UK narrow gauge locomotive manufacturers used external plate frames i.e. the wheels were on the inside with the conrods connecting to flycranks. This made it very easy for manufacturers to have a variable gauge locomotive from one set of plans.

When I build a locomotive I have designed my own adaptable system which is based on a sturdy baseplate to which I attach everything. Thus what appears to be plate frames with a walkway around it is actually a sheet with the plate frames split in two and then affixed top and bottom.

The following pictures show the construction of the Dispatch 12 wheeler model. The sheet of ply has been cut and is edged with quadrant.

See Picture2.

The next picture shows the cab front and boiler have been made as have the two wing tanks. The wood slat flooring is made from spatulers trimmed to size with a pair of wire cutters.

See Picture 3.

When it comes to the bogies for the carriages and wagons -here I have to admit that I find the bar type to be more attractive than the english plate type. Although if I were to build my own bogies I suspect they would be of the plate type -for ease of manufacture...