If an engine, of the class represented as pulling our train, passes over the top of the grade with half an inch of water in the glass, there will be about 700 gallons in the boiler. Now, suppose it runs down the hill without using steam, and keeps pumping till the water rises six inches in the glass, there will be about 200 gallons more water in the boiler. It is no unusual thing to do this with a mild fire, and yet have no diminished tension of steam shown by the gauge, although 200 gallons of water of about 60 degrees have been injected amongst 700 gallons at 361 degrees, the temperature due to a steam-pressure of 140 pounds. This ought to reduce the mean temperature below 300 degrees, yet the pointer of the steam-gauge keeps indicating 140. That the pressure of steam and the temperature of the water do not accord, is shown directly the throttle is opened to perform work. The brisk circulation due to the rush of steam through the dry pipe now brings the temperature of water and steam to equilibrium, and backward the index of the steam-gauge travels. The steam-pressure goes back faster than is due to the supply drawn for the cylinders; because the latent heat of the steam passes into the water, helping to bring the whole contents of the boiler to an even temperature.
SOME EFFECTS OF INJUDICIOUS BOILER-FEEDING.
Meanwhile, with an engine operated in this fashion, the train will probably stand for fifteen minutes, till sufficient steam is raised to proceed with.
The fact that newly injected water does not immediately rise in temperature to the heat indicated by the pressure-gauge, can also be tested by filling up a boiler with an injector while the engine is at rest on a side-track. Working an injector causes greater circulation than feeding with a pump, and the water goes into the boiler at a higher temperature. For this reason the injector is superior to the pump as a feeding-medium. But, if the engineer pulls out directly after filling up the boiler with an injector, the steam will go down a few pounds, no matter how good a fire may be on the grates.
On level roads, the pump or injector should be set to supply the needs of the boiler; and a skillful engineer can regulate this so well, that the foot-cock has seldom to be moved. The best results in getting trains over the road, and in preserving boilers, are obtained in this way. The runner who adopts the intermittent system of feeding is always in trouble, or, as the boys say, “he is always nowhere.”
CAREFUL FEEDING AND FIRING PRESERVE BOILERS.
A case where the conservative effect of careful firing and feeding was strikingly illustrated, came under the author’s notice a year or two ago. During the busiest part of the season, the fire-box of a freight engine belonging to a Western road became so leaky that the engine was really unfit for service. Engines, like individuals, soon lose their reputation if they fail to perform their required duties for any length of time. This engine, “29,” soon became the aversion of train-men. The loquacious brakeman, who can instruct every railroad-man how to conduct his business, but is lame respecting his own work, got presently to making big stories out of the amazing quantity of water and coal that “29” could get away with, and how many trains she would hold in the course of a trip. The road was suffering from a plethora of freight, and extreme scarcity of engines; and on this account the management was reluctant to take this weakling into the shop. So the master mechanic turned “29” over to Engineer Macleay, who was running on a branch where delays were not likely to hold many trains. Mac deliberated about taking his “time” in preference to the engine, which others had rejected, but finally concluded to give the bad one a fair trial. The first trip convinced the somewhat observant engineer that the tender fire-box was peculiarly susceptible to the free use of the pump, and to sudden changes of the fire’s intensity of heat. So he directed the fireman to fire as evenly as possible, never to let the grates get bare enough to let cold air pass through, to keep the door closed except when firing, to avoid violent shaking of the grates, and never to throw more than three or four shovelfuls of coal into the fire-box at one time. His own method was, to feed with persistent regularity, to go twice over heavy parts of the division in preference to distressing the engine by letting the water get low, and then filling up rapidly. This system soon began to tell on the improved condition of the fire-box. The result was, that, within a month after taking the engine, Mac was pulling full trains on time; and this he continued to do for five months, till it was found convenient to take the engine in for rebuilding.
OPERATING THE DAMPERS.
According to the mechanical dictionary, a damper is a device for regulating the admission of air to a furnace, with which the fire can be stimulated, or the draught cut off, when necessary. Some runners regard locomotive dampers in a very different light. They seem to think the openings to the ash-pan are merely holes made to let air in, and ashes out; that doors are placed upon them, which troublesome rules require to be closed at certain points of the road to prevent causing fires. Those who have made their business a study, however, understand that locomotive dampers are as useful, when properly managed, as are the dampers of the base-burner which cheers their homes in winter weather. To effect perfect combustion in the fire-box, a certain quantity of oxygen, one of the constituents of common air, is required to mix with the carbon and carbureted hydrogen of the coal. The combination takes place in certain fixed quantities. If the quantity of air admitted be deficient, a gas of inferior calorific power will be generated. On the other hand, when the air-supply is in excess of that needed for combustion, the surplus affects the steam-producing capabilities of the fire injuriously; since it increases the speed of the gases, lessening the time they are in contact with the water-surface, and a violent rush of air reduces the temperature of portions of the fire-box below the heat at which carbureted hydrogen burns.