PRESERVATION OF BOILERS.
The preservation of a boiler depends very much upon the care and attention bestowed upon it by the engineer, and no other person is so much interested in its safety. To prevent undue strains from being put upon the boiler, the engineer should see that the safety-valves and the steam-gauge are kept in proper order. To secure this, the steam-gauge should be tested at least once a month. The rule established on well-conducted roads, prohibiting engineers from interfering with safety-valves, is a very judicious one; and no persons are more interested in its strict observance than the engineers themselves.
CAUSING INJURY TO BOILERS.
Some men are idiotic enough to habitually screw down safety-valves, that the engine may be able to overcome heavy grades without doubling. This is criminal recklessness, and all train men are interested in its suppression. Low water has often been blamed falsely as the cause of disaster to boilers; a theory having prevailed, that permitting the water to become low led to the generation of an explosive gas which no sheet could withstand. That theory was exploded long ago; but, nevertheless, it is certain that low water paves the way for explosions by deteriorating the fire-box sheets, and destroying stay-bolts. A careful engineer watches to prevent his engine from getting “scorched” even slightly; for the smallest scorching may yield a harvest of trouble, even after many days. The danger of scorching is most imminent when an engine is foaming badly from the effects of impurities in the feed-water or in the boiler. At such a time the water rises so lavishly with the steam, that the gauges are no indication of the true water-level. The steam must be shut off to find the true level of the water. Where this trouble is experienced, the engineer should err on the safe side, even though untold patience is needed to work the engine along with the boiler full of water.
DANGERS OF MUD AND SCALE.
Mud within the boiler, and scales adhering to the heating surface, are dangerous enemies to the preservation of boilers; and engineers should strive to prevent their evil effects by rooting them out so far as practicable. Much can be banished by washing out frequently; and scales can, to some extent, be prevented by selecting the softest water on the road. If water in a tank is so hard that it makes soap curdle instead of lather when a man attempts to wash with it, that tank should be avoided as far as possible.
BLOWING OFF BOILERS.
The sudden cooling down of boilers, by blowing them off while hot, is a most pernicious practice, which is responsible for many cracked sheets and broken stay-bolts. It also tends to make a boiler scale the heating surfaces rapidly. Every time a boiler is blown out hot, if the water contains calcareous solution, a coat of mud is left on the heating surfaces, which dries hard while the steel is hot. If a piece of scale taken from a boiler periodically subjected to this blowing-out process be closely examined, it will be found to consist of thin layers, every one representing a period of blowing off, just as plainly as the laminæ of our rocks indicate the method of their formation. When a boiler must be cooled down quickly for washing out or other purposes, the steam should be blown off, and the boiler gradually filled up with water. Then open the blow-off cock, and keep water running in about as fast as it runs out until the temperature gets even with the atmosphere. The boiler may now be emptied without injury. Or another good plan is to blow off about two gauges of water under a pressure of forty or fifty pounds of steam, then cool down the boiler gradually, to prepare for washing.
Although the dangers of blowing off hot boilers, and then rushing in cold water to wash out, are well known and acknowledged, yet the practice is still followed on many roads where more intelligent action might be expected.