BEGINNING TO BUILD A “PACIFIC” EXPRESS LOCOMOTIVE AT DONCASTER WORKS. The main frames in position.
AS a house is built upon a foundation, so with a locomotive engine. The locomotive “foundation” consists of the two “main frames”, running parallel to each other throughout the whole length of the engine. In British locomotives the frames are of steel plate, about 1¼ inches thick, and from 2 to 3 feet deep; they are set up on edge and very strongly connected together by cross-
In the course of erecting the engine at the works where it is built, the first operation is that of laying down the main frames. To them the cylinders are bolted, together with all the details of the “motion”, which controls the entrance of steam into the cylinders and its exit from them, and also transforms the straight-
BUILDING AN ENGINE AT SWINDON WORKS: main frames, showing cylinders and saddle for smoke-
The problem of “bearings”— that is, the points where two metallic surfaces rub together when the engine is in motion — is vastly different in a full-
The same applies, of course, to cylinders and motion, and nowadays the oil is usually fed to the moving parts by some means of “forced” lubrication, under pressure. A mechanical lubricator numbered (8) appears in one of the photographs on this page; it has fourteen “feeds” to different moving parts of the engine. Very often now this lubrication is carried on by an apparatus inside the driver’s cab, so that he can see all the time whether the various vital parts of the motion are getting their proper supply of oil. In the old days this meant a walk round the front of the engine while it was in motion, but all such perilous practices have long since been done away with. Even with all these precautions, however, engines will sometimes “run hot”, by small grit getting into the bearings, or from other causes; and running hot means a temporary withdrawal from service, until the defect has been remedied.
PORTABLE APPARATUS for Measuring Wheel-
Between the main frames of the engine and the axle-
Next in order for our consideration come the cylinders. Every locomotive has at least two cylinders, and sometimes there are three, or even four. In a two-
DRIVING AXLE of a “Castle” class engine, Great Western Railway, showing balanced cranks.
But the disadvantage of inside cylinders is that the driving-
The locomotive designer in this country works under considerable difficulties, owing to the narrow limits of space into which his engine must fit in order not to foul any of the structures over or at the side of the line. These considerations seriously affect the size of cylinders in our bigger engines. The biggest outside cylinders which a British locomotive can carry without fouling the platforms are of 22 inches internal diameter; they may be seen, for example, on the big 4-
But the boilers of to-
The two “cranks” of a two-
But a three cylinder simple engine can always be distinguished by its rapid puffing; in this case there are only three cranks to divide up the circle, into three angles of 120 degrees each, and there are therefore six independent puffs to each revolution of the driving wheels. The home of the three cylinder simple is the London and North Eastern Railway, which has large numbers of such engines ; there are the big “Pacifics” of the “Flying Scotsman” type, the three-
A NEAR VIEW OF THE VALVE-
You will notice in this photograph the end of the “piston-
At this stage it is well to say something about the valve-
At each end of the cylinder there are openings in its walls known as ports; they are for the admission and exit of the steam. Flat slide-
We will assume that the port at one end of the cylinder is open to steam, which flows in and pushes the piston from that end of the cylinder to the other; the complete travel is known as the “stroke”. The piston pushes the piston-
The moment that the wheel has turned beyond the point at which the crank-
The valve has another very important function. Steam is not admitted to the cylinder during the whole time that the piston is travelling from one end to the other; the boiler of the engine could never supply steam rapidly enough for that. At the moment of starting, steam is admitted for about three-
This is known as “expansive working”, because so much use is made of the expansive properties of the steam; and in general, the more the use made of expansion—that is, the earlier the rate of cut-
Before closing this chapter, a word of explanation is needed in regard to compound locomotives. The idea behind compounding is to divide the expansion of the steam into two stages. Two sets of cylinders are provided, therefore: “high-
In compound locomotives arrangements are generally made whereby, on starting, the driver can admit boiler steam straight down to the low-
In America, also, nothing much has been done in the way of locomotive compounding, but when we turn to the Continent of Europe, it is safe to say that the majority of the larger locomotives in its various countries are of compound types. France and Germany, in particular, are the home of compound engines, and those of you who have travelled over the Northern Railway of France between Calais and Paris will have had, no doubt, all the demonstration you need as to what can be done by their big compound “Pacifics” in the way of fast travelling. On the Calais and Boulogne boat expresses, which are only allowed one hundred and ten minutes in which to cover the 109 miles from Paris to Abbeville, they think nothing of gaining time with huge trains of 500 tons’ weight. But it is probable that we shall see a further development of locomotive compounding in this country ere long.