CYLINDER (STEAM LOCOMOTIVE)

'Steam locomotive cylinders' may be arranged in several different ways. On early locomotives (e.g. Puffing Billy) they were often set vertical and the motion was transmitted through beams, as in a beam engine.

Contents

Direct drive

Inside or outside cylinders

Three or four cylinders

Valves

Inside cylinders

Outside cylinders

Valve gear

Inside cylinders

Outside cylinders

Three cylinders

Four cylinders

Other variations

See also

Sources

Direct drive

The next stage (e.g. Stephenson's Rocket) was to drive the wheels directly from steeply inclined cylinders placed at the back of the locomotive. Direct drive became the standard arrangement but the cylinders were moved to the front and placed either horizontal or nearly horizontal.

Inside or outside cylinders

The front-mounted cylinders could be placed either inside (between the frames) or outside. Examples:

★ Inside cylinders, Planet locomotive

★ Outside cylinders, GNR Stirling 4-2-2
In the 19th and early 20th centuries, inside cylinders were widely used in the UK but outside cylinders were more common in Continental Europe and the USA. The reason for this difference is unclear. From about 1920, outside cylinders became more common in the UK but many inside-cylinder engines continued to be built.

Three or four cylinders

The demand for more power led to the development of engines with three cylinders (two outside and one inside) or four cylinders (two outside and two inside). Examples:

★ Three cylinders, SR Class V

★ Four Cylinders, LMS Princess Royal Class

Valves

The 'valve chests' or 'steam chests' which contain the slide valves or piston valves may be located in various positions.

Inside cylinders

If the cylinders are small, the valve chests may be located between the cylinders. For larger cylinders the valve chests will be on top of the cylinders.

Outside cylinders

The valve chests are usually on top of the cylinders but, in older locomotives, the valve chests were sometimes located alongside the cylinders and inserted through slots in the frames. This meant that, while the cylinders were outside, the valves were inside and could be driven by inside valve gear.

Valve gear

There are many variations in the location of the valve gear. In British practice, inside valve gear is usually of the Stephenson type while outside valve gear is usually of the Walschaerts type. However, this is not a rigid rule and most types of valve gear are capable of being used either inside or outside. Joy valve gear was once popular, e.g. on the LNWR G Class.

Inside cylinders

On inside cylinder engines the valve gear is nearly always inside (between the frames), e.g. LMS Fowler Class 3F.

Outside cylinders

On engines with outside cylinders there are three possible variations:

★ Inside valve gear driving inside valves, e.g. NER Class T2

★ Inside valve gear driving outside valves through rocking shafts, e.g. GWR 4900 Class

★ Outside valve gear driving outside valves, e.g. LSWR N15 Class

Three cylinders

There are three common variations:

★ Three sets of valve gear (two outside, one inside), e.g. LNER Peppercorn Class A2

★ Outside valve gear driving the outside valves. Inside valve driven by Gresley conjugated valve gear, e.g. LNER Class A1/A3

★ Three sets of inside valve gear (all valves inside), e.g. NER Class T3

Four cylinders

There are three common variations:

★ Four sets of valve gear (two outside, two inside), e.g. SR Lord Nelson Class

★ Inside valve gear driving the inside valves directly and the outside valves via rocking shafts, e.g. GWR 4073 Class

★ Outside valve gear driving the outside valves directly and the inside valves via rocking shafts, e.g. LMS Princess Coronation Class

Other variations

There are many other variations, e.g. geared steam locomotives which may have only one cylinder.

See also

★ Steam locomotive components

★ Hydrolock

Sources

★ Linked Wikipedia articles