Spark Losses. From the diagram shown in Fig. 57, it is evident that one of the principal heat losses is that of sparks. By the term sparks is meant the small particles of partially burned coal which are drawn through the flues and ejected through the stack by the action of the exhaust. In the operation of a locomotive, it has been demonstrated that the weight of sparks or cinders increases with the rate of combustion and may reach a value of from 10 to 15 per cent of the total weight of coal fired. Damage suits frequently arise, due to fires started by cinders thrown from the stack of the locomotive. Experiments have shown, however, that sparks from a locomotive will not be likely to start fires beyond the right of way.

High Steam Pressures. With the development of high-power locomotives came the use of high steam pressures. At first, only very low pressures were carried but soon 200 pounds pressure per square inch became very common and 220 and 225 not unusual. But with the increase of pressure there came an increase in trouble due to bad water, leaky flues, and an increase in incidental leaks in the boiler. All of these factors affected the performance of the locomotive. To determine to what extent the economic performance of the boiler was affected by an increase of steam pressure and also the most economical steam pressure to use, a series of tests were carried out at Purdue University. The following are the conclusive results as read before the Western Railway Club by Dean W. F. M. Goss:

THE EFFECT OF DIFFERENT PRESSURES UPON BOILER PERFORMANCE

1. The evaporative efficiency of a locomotive boiler is but slightly affected by changes in pressure between the limits of 120 pounds and 240 pounds.

2. Changes in steam pressure between the limits of 120 pounds and 240 pounds will produce an effect upon the efficiency of the boiler which will be less than one-half pound of water per pound of coal.

3. It is safe to conclude that changes of no more than 40 or 50 pounds in pressure will produce no measurable effect upon the evaporative efficiency of the modern locomotive boiler.

Table of Contents; Page 58; Page 62; Index

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