The Three-Cylinder Compound Locomotives

By A. Oliver

First published in 1928, this is a classic guide to a the Three-Cylinder Compound Locomotive, a type of steam-powered engine used in trains. The first example of such an engine was built for the old Midland Railway in January, 1902. With detailed explanations and simple diagrams, this volume provides a complete overview of the engine and its inner workings. Highly recommended for vintage locomotive enthusiasts. Contents include: “Air Valves”, “Action in the Cylinders”, “Arithmetic”, “Bye-Pass Valves”, “Compound Expansion of Steam”, “Compound System Adopted”, “Compound Regulator Valve”, “Carbonation”, “Failures and Remedies”, “Handling the Engine”, “Horse Power”, “Leading the Engine”, “Horse Power”, “Leading Dimensions and Rations”, “Lubrication”, “Non-Return Valves”, etc. Many vintage books such as this are increasingly scarce and expensive. It is with this in mind that we are republishing this volume now in an affordable, modern, high-quality edition complete with a the original text and artwork.

• Language: English
• Publisher: Home Farm Books
• Release date: Feb 22, 2018
• ISBN: 9781528784900

Book preview

THE THREE-CYLINDER COMPOUND LOCOMOTIVES

(MIDLAND SECTION), L. M. S. R.

Compound Expansion of Steam.

The high boiler pressures used in modern locomotive practice make it necessary to work with a large number of expansions of steam in the cylinders; that is, if the most economical use is to be made of the fuel and water. Several disadvantages attend excessive expansion of steam in a single cylinder. In the first place, a very early cut-off would be required, whereby to obtain the lowest possible release pressure, and to secure that in the most efficient way, the volume of the cylinder would have to be large enough to accommodate the large volume occupied by the steam at this attenuated pressure. The wide temperature range, too, as between that on admission and that at release, would be excessively large, giving rise to considerable losses due to initial condensation. Also since the mean (average) effective pressure on the piston would be only a small fraction of the high initial steam pressure, the diameter of the cylinder would have to be very large to develop the power required; and, further, all the working parts would require to be robust in design to withstand the high initial pressure. The combined effect of these disadvantages—ruling out the advantages incidental to the use of super-heated steam—would result in a locomotive of excessive size and weight, which would be uneconomical in working for two main reasons, namely, the high steam consumption entailed by excessively large initial condensation, and the comparatively low mechanical efficiency resulting from the large frictional resistance unavoidable from heavy moving parts. The expansions of steam in the cylinder of a saturated simple locomotive are limited to about four, as indicated in Fig. 1, and where a higher grade expansion of steam than that is required compound expansion is employed. This carried out in one high-pressure and two low-pressure cylinders of such volume as to secure that the work done by the two low-pressure cylinders is the equivalent of that done by the single high-pressure cylinder reduces the initial condensation (therefore the steam consumption), .diminishes the range of stress on the working parts, and secures a more uniform turning effort at the crank shaft.

FIG. 1.

Principle of Compounding.

This will be readily understood by a reference to Fig. 2. At A is a cylinder enclosing two pistons arranged on the rod P R. Steam is allowed to enter the cylinder at S S, and since the piston heads are of equal diameter and therefore balanced, no movement of the pistons take place. The pistons may, however, be made to move provided steam is also admitted at P., this steam balancing the piston at P. but unbalancing the one near P.R. Both pistons will, therefore, move as indicated by the arrow at P, and with a force equal to that acting at the piston near P.R.

FIG. 2.

At B, Fig. (2), are arranged two cylinders, one twice the diameter of the other. Since the square of one is one and the square of two is four, it follows that the large cylinder will be as four is to one in the small cylinder. If steam be admitted at S.S. the steam will act at the two pistons in opposite directions, but, since the small piston is but one-fourth that of the large piston, it follows that both pistons will move in the direction of p.p., and with a force proportional to the difference in the square inch area of the two pistons.

Now assume that live steam is cut off at S.S. and, instead, admitted at P. where it will move the piston in the direction of the arrow. The piston having completed its stroke, the steam will then be exhausted into a low pressure receiver which communicates alternately to the two sides of the large piston. Since this exhaust steam will act on the small piston in a direction opposite to its motion, it follows that the amount of retardation experienced by the small piston will be as the difference between the live steam pressure at one side and the exhaust steam pressure at the other. If the live steam pressure is 180lb. per sq. in. and the exhaust steam pressure 60lb. per sq. in., the effective steam pressure on the small piston will be 120lb. per sq. in.

Next assume that exhaust steam from the small cylinder enters at S.S. with a pressure of 60lb. per sq. in. Since the large piston is four times the area of the small piston, it follows that the large piston will move with a force ratio of 240 as to 120 acting effectively at the small piston. If two L.P. cylinders of equivalent diameter to the H.P. cylinder were used, with 180lb. at the H.P. and 60lb. at the L.P., then, in that case, the two L.P. cylinders would be equal to the one H.P., since the effective pressure at the H.P. would be 120lb. In such a three cylinder compound engine the H.P. cylinder would do one-half the work, and the two L.P. cylinders combined the other half.

Three Cylinder Compound Locomotives (Midland Section) L. M. S. R.

LEADING DIMENSIONS AND RATIOS.