gauge-cocks should be tried and the water level determined. After it has been found that the water is not too low, the banked fires may be pulled down and spread over the grates and allowed to burn up slowly, the damper regulator, if one is fitted, in the meantime having been connected.

Blowing Down.-While the fires are burning up and before the pressure begins to rise, the blow-off cock or valve should be opened and the boiler blown down; that is, a small quantity of the water should be blown out. This should be done every morning, so that any impurities in mechanical suspension in the water that settled during the night may be removed. Great care should be exercised while doing this so that too much water is not blown out; from 3 to 4 in. as shown by the gauge glass, is sufficient. Under no circumstances should the attendant leave the blow-off while it is open. Disaster to the boiler is liable to follow a disregard of this injunction. Next, all the valves, except the stop-valve, which were shut the night before should be opened and tried to see that they are free and in good working order.

CARE OF BOILERS

Safety Valves. Great care should be exercised to see that the safety valves are ample in size and in working order. Overloading or neglect frequently lead to the most disastrous results. Safety valves should be tried at least once every day, to see that they act freely.

Pressure Gauge. The steam gauge should stand at zero when the pressure is off, and it should show the same pressure as that at which the safety valve is set when that is blowing off. If the pressures do not agree, the gauge should be compared with one known to be correct.

Water Level. The first duty of an engineer before starting, or at the beginning of his watch, is to see that the water is at the proper height. He should not rely on glass gauges, floats, or water alarms, but try the gauge-cocks. If they do not agree with the water gauge, the cause should be learned and the fault corrected.

Gauge-Cocks and Water Gauges. All gauge-cocks and water gauges must be kept clean. Water gauges should be blown out frequently, and the glasses and passages to them kept clean. The Manchester, England, Boiler Association attributes more accidents to inattention to water gauges than to all other causes put together.

Feed-Pump or Injector.-The feed-pump or injector should be kept in perfect order, and be of ample size. No make of pump can be expected to be continuously reliable without regular and careful attention. It is always safe to have two means of feeding a boiler. Check-valves and selfacting feed-valves should be frequently examined and cleaned. The attendant should satisfy himself frequently that the valve is acting when the feed-pump is at work.

Low Water.-In case of low water, immediately cover the fire with ashes (wet if possible) or any earth that may be at hand. If nothing else is handy, use fresh coal. Draw fire as soon as it can be done without increasing the heat. Neither turn on the feed, start nor stop engine, nor lift safety valve until fires are out and the boiler cooled down.

Blisters and Cracks.-Blisters and cracks are liable to occur in the best plate iron. When the first indication appears, there must be no delay in having the fault carefully examined and properly cared for.

Fusible Plugs.-When used, fusible plugs must be examined when the boiler is cleaned, and carefully scraped clean on both the water and fire sides, or they are liable not to act.

Firing. Fire evenly and regularly, a little at a time. Moderately thick fires are most economical, but thin firing must be used where the draft is poor. Take care to keep grates evenly covered, and allow no air holes in the fire. Do not clean fires oftener than necessary. With bituminous coal, a coking fire, i. e., firing in front and shoving back when coked, gives best results, if properly managed.

Cleaning.-All heating surfaces must be kept clean outside and in, or there will be a serious waste of fuel. The frequency of cleaning will depend on the nature of fuel and water. When a new feedwater supply is introduced, its effect on the boiler should be closely observed, as this new supply may be either an advantage or a detriment as compared with the working of the boiler previous to its introduction. As a rule, never allow overin. of scale or soot to collect on surfaces between cleanings. Handholes should be frequently removed and surfaces examined, particularly in the case of a new boiler, until proper intervals have been established by experience.

The exterior of tubes can be kept clean by the use of blowing pipe and hose through openings provided for that purpose. When using smoky fuel, it is best to occasionally brush the surfaces when steam is off.

Hot Feedwater.-Cold water should never be fed into any boiler when it can be avoided, but when necessary it should be caused to mix with the heated water before coming in contact with any portion of the boiler.

Foaming. When foaming occurs in a boiler, checking the outflow of steam will usually stop it. If caused by dirty water, blowing down and pumping up will generally cure it. In cases of violent foaming, the draft and fires should be checked.

Air Leaks. Be sure that all openings for admission of air to boiler or flues, except through the fire, are carefully stopped; this is frequently an unsuspected cause of serious waste of fuel.

Blowing Off.-If feedwater is muddy or salt, blow off a portion frequently, according to condition of water. Empty the boiler every week or two, and fill up afresh. When surface blow cocks are used, they should be often opened for a few minutes at a time. Make sure no water is escaping from the blow-off cock when it is supposed to be closed. Blow-off cocks and check-valves should be examined every time the boiler is cleaned. Never empty the boiler while the brickwork is hot.

Leaks. When leaks are discovered, they should be repaired as soon as possible.

Filling Up.-Never pump cold water into a hot boiler. Many times leaks, and, in shell boilers, serious weaknesses, and sometimes explosions are the result of such an action.

Dampness. Take care that no water comes in contact with the exterior of the boiler, as it tends to corrode and weaken it. Beware of all dampness in seatings and coverings.

Galvanic Action.-Examine frequently parts in contact with copper or brass, where water is present, for signs of corrosion. If water is salt or acid, some metallic zinc placed in the boiler will usually prevent corrosion, but it will need attention and renewal from time to time.

Rapid Firing. In boilers with thick plates or seams exposed to the fire, steam should be raised slowly, and rapid or intense firing avoided. With thin water tubes, however, and adequate water circulation, no damage can come from that cause.

Standing Unused. If a boiler is not required for some time, empty and dry it thoroughly. If this is impracticable, fill it quite full of water, and put in a quantity of common washing soda. External parts exposed to dampness should receive a coating of linseed oil.

Repair of Coverings.-All coverings should be looked after at least once a year, given necessary repairs, refitted to the pipe, and the spaces due to shrinkage taken up. Little can be expected from the best non-conductors if they are allowed to become saturated with water, or if air-currents are permitted to circulate between them and the pipe.

General Cleanliness.-All things about the boiler room should be kept clean and in good order; negligence tends to waste and decay.

BOILER INSPECTION

NATURE OF INSPECTION

The inspection of a boiler usually consists in an external examination of the complete structure, and of the setting if the boiler is externally fired, and an internal inspection. The examination of the boiler consists of an ocular inspection for visible defects, and a hammer test or sounding for hidden defects of plates, stays, braces, and other boiler parts. The hammer test is made by tapping the suspected parts with a light hammer and judging the existence and extent of defects from the sound produced by the blow. If the examination discloses marked wear and tear, a series of calculations is often required to find the safe pressure that may be allowed on the worn parts, using such formulas or rules as laws, ordinances, and regulations may prescribe. In the absence of officially prescribed formulas and rules, the inspector should use such rules as he deems in best accordance with good practice. The inspection is usually, but not always, completed by a so-called hydrostatic test, which is generally prescribed by official regulations.

EXTERNAL INSPECTION

Preparation. Before a boiler that has been in use can be inspected, it must be blown out and must be allowed to cool off. As soon as the water has been removed, the manhole covers, handhole covers, and washout plugs should be taken out and all loose mud and scale washed out with a hose. If the boiler is externally fired, the tubes must be swept and the furnace, the ash-pit, the smokebox, and the space back of the bridge wall must be cleaned out. Any removable insulating covering that prevents the inspector from having free access to the exterior of the boiler must be removed to the extent deemed necessary by him; it may even be necessary to take down some of the bricks of the setting.

Inspection of Externally Fired Boilers. In the inspection of an externally fired fire-tube or flue boiler, the exterior is first examined. The seams are gone over inch by inch; the rivet heads and calking edges of the plates are carefully scrutinized for evidence of leaks; and possible cracks are looked for between the rivet heads, especially in the girth seams and on the under side of the boiler. The plates must also be examined for corrosion, bulges, blisters, and cracks. The heads are inspected for cracks between the tubes or flues, cracks in the flanges, leaky tubes, and leaks in the seams. The condition of the firebrick lining of the furnace and bridge and the top of the rear combustion chamber is noted while making the exterior examination of the underside of the boiler. Every defect that is found should be clearly marked. Attention must also be paid to the condition of the grate bars and their supports.

Inspection of Internally Fired Boilers.-The inspection of the shell and heads must be followed by examination of the fire-box or furnace tubes or flues, and of the combustion chambers if these are fitted inside the boiler. In fire-boxes, special attention must be paid to the crown sheet. The ends of the staybolts require close examination; if such ends are provided with nuts, these must be examined, as they are liable to loosen and are also liable to be burned off in time. Each staybolt should be tested for breakage, which is done by holding a sledge against the outside end of the staybolt and striking the inner, or fire-box, end with a light hammer; in making this test on the boilers of locomotives it is customary, when practical, to subject the boiler to an internal air pressure of from 40 to 50 lb. per sq. in. The internal pressure, by bulging the sheets, separates the ends of a broken staybolt, which renders it comparatively easy to find them by the hammer test.

Inspection of New Boilers.-As made in boiler shops, the external inspection of new boilers, whether they are internally or externally fired, and whether they are of the water-tube or the fire-tube type, usually consists in a thorough examination for visible defects and testing under water pressure to locate leaks. If a new boiler subject to official inspection during construction successfully passes such a hydrostatic test as the regulations prescribe, it will usually be permitted the working pressure it was designed for, the design having been approved officially before construction. The working pressure will be reduced, however, if the inspection discloses poor workmanship.

In the external inspection of water-tube boilers that have been in use, the tubes that are exposed directly to the heat of the fire must be particularly well examined for evidence of overheating. The plugs or handholes placed in headers to permit the insertion of the tubes and the cleaning of them are inspected for leakage, and the headers are inspected for cracks. Steam drums and mud-drums should be examined as carefully and for the same defects as the shells of externally fired fire-tube boilers. The fire-brick lining of the furnace, and the interior of the brick setting in general, as well as the baffle plates controlling the direction of flow of the gases of combustion, must be examined for cracks and any other defects. The external inspection of the setting can usually be made very rapidly, as everything is in plain sight.

INTERNAL INSPECTION

Preparation. Before the internal inspection is begun all loose mud should be washed out with a hose. In a horizontal return-tubular boiler and flue boiler, the shell plates and heads should be examined for corrosion and pitting; if the boiler has longitudinal lap seams, these should be inspected at the inside calking edge for incipient grooving and cracks. All seams should be examined for cracks between the rivet holes. Obviously, if the boiler is scaled to an appreciable degree, the scale must be removed before inspection. The tubes or flues should be examined for pitting, as well as for uniform corrosion. All braces should be inspected by sounding them with a hammer, and if they are attached by cotter pins, it should be seen to that these are firmly in place.

All defects found should be marked; it is good practice to make a memorandum of them as well. If any of the bracing seems to have worn considerably, it should be measured at the smallest part in order that the safe working pressure thereon may be calculated afterwards. To determine to what thickness a plate attacked by uniform corrosion has been reduced the inspector will have one or more holes drilled through the plate in the worn part to enable him to measure the thickness. These holes are afterwards plugged, generally by tapping out and then screwing in a plug.

Inspection of Locomotive-Type Boilers.-In internally fired boilers of the fire-box and locomotive type, particular attention must be paid to the crown bars, crown bolts, and sling stays; in boilers having the crown sheet stayed by radial staybolts, special attention is also paid to these. As a general rule, the inspector can make only an ocular inspection of most of them, as they are beyond his reach; where the outer sheets of the firebox contain inspection or washout holes above the level of the crown sheet, a lighted candle tied or otherwise fastened to a stick can usually be introduced through these holes from the outside by a helper. In inspecting above the crown sheet, the inspector should look for mud between the crown sheet and crown bars and sight over the top of the bars to see if any have been bent. As the inspector can reach from the inside of the boiler only a few of the staybolts staying the sides of the firebox, he must rely on the hammer test applied from the inside of the furnace for finding broken staybolts.

Flues and Combustion Chambers.-In boilers having circular furnace flues and internal combustion chambers, the top of the furnace flues must be carefully inspected for deposits of grease and scale, which are especially liable to be found if the feedwater is obtained from a surface condenser. Even a light deposit of grease on the furnace flue is liable to lead to overheating and subsequent collapse of the top. The tops of the combustion chambers, together with their supports, are usually casily inspected, there being ample space to reach every part.

Inspection of Vertical Boilers.-Vertical boilers as a general rule, except in the largest sizes, have no manhole to admit a person to the inside, and such internal inspection as is possible must be made through the handholes. Defects to be looked for are pitting and uniform corrosion of the shell and tubes near the usual water-line, and cracks in the heads between the tubes, the lower head being especially liable to show this injury.

INSPECTION OF FITTINGS

Inspection of Safety Valve.-The safety valve requires very careful inspection. If this valve is known to leak, it should be reseated and reground before the hydrostatic test is made. After a boiler passes the hydrostatic test, the clamp locking the safety valve is removed, and by running the pressure up once more, the point at which the safety valve opens can be noted by watching the steam gauge, which is supposed to have been tested and corrected. If the safety valve does not open at the working pressure allowed or opens too soon, it is readjusted. If the safety valve is locked by a seal, as is often required by official regulations, the seal is applied after adjustment of the valve.

Testing of Steam Gauge.-The steam gauge should be tested before the hydrostatic test and at each inspection with a so-called boiler inspector's testing outfit. If the gauge under test is more than 5% incorrect most inspectors will condemn it although some will condemn gauges showing a much smaller In most cases the gauge can be repaired at small expense by the makers. Inspection of Water Gauge and Blow-off.-The connections of water column and water-gauge glasses require examination in order to see that they are clear throughout their whole length. The blow-off pipe also requires examination in order to see that it is clear.

error.

SELECTION OF BOILERS

General Requirements.-When choosing a boiler, the facts to be kept in mind are:

1. The grate surface must be sufficient to burn the maximum quantity of coal expected to be used at any time, taking into consideration the available draft, the quality of coal, its percentage of ash, whether or not the ash tends to run into clinker, and the facilities, such as shaking grates, for getting rid of the ash or clinker.

2.

The furnace must be adapted to burn the particular kind of coal used.

3. The heating surface must be sufficient to absorb so much of the heat generated that the gases escaping into the chimney will be not over 450° F. with anthracite, and 550° F. with bituminous coal.

4. The gas passages must be so designed and arranged as to compel the gas to traverse at a uniform rate the whole of the heating surface, being not so large at any point as to allow the gas to find a path of least resistance, or shortcircuiting, or, on the other hand, so contracted at any point as to cause an obstruction to the draft.

When these elements are found in any boiler-and they may be found in boilers of many of the common types-the relative merits of the different types may be considered with reference to their danger of explosion; their probable durability; the character and extent of repairs that may be needed from time to time, and the difficulty, delay, and expense that these may entail; the accessibility of every part of the boiler to inspection, internal and external; the facility for removal of mud and scale from every portion of the inner surface, and of dust and soot from the exterior; the water and steam capacity; the steadiness of water level; and the arrangements for securing dry

steam.

Liability to Explosion.-All boilers may be exploded by overpressure, such as might be caused by the combination of an inattentive fireman and an inoperative safety valve, or by corrosion weakening the boiler to such an extent as to make it unable to resist the regular working pressure; but some boilers are much more liable to explosion than others. When selecting a boiler, it is well to see whether or not it has any of the features that are known to be dangerous. The plain cylinder boiler is liable to explosion from strains induced by its method of suspension, and by changes of temperature. Alternate expansion and contraction may produce a line of weakness in one of the rings, which may finally cause an explosion. A boiler should be so suspended that all its parts are free to change their position under changes of temperature without straining any part. The circulation of water in the boiler should be sufficient to keep all parts at nearly the same temperature. Cold feedwater should not come in contact with the shell, as this will cause contraction and strain.

The horizontal tubular boiler, and all externally fired shell boilers, are liable to explosion from overheating of the shell, due to accumulation of mud, scale, or grease, on the portion of the shell lying directly over the fire, to a double thickness of iron with rivets, together with some scale, over the fire, or to low water uncovering and exposing an unriveted part of the shell directly to the hot gases.

Vertical tubular boilers are liable to explosion from deposit of mud, scale, or grease, upon the lower tube-sheet, and from low water allowing the upper part of the tubes to get hot and cease to act as stays to the upper tube-sheet. Locomotive boilers may explode from deposits on the crown sheet, from low water exposing the dry crown sheet to the hot gases, and from corrosion of the staybolts.

Double-cylinder boilers, such as the French elephant boiler, and the boilers used at some American blast furnaces, have exploded on account of the formation of a steam pocket on the upper portion of the lower drum, the steam being prevented from escaping from out of the rings of the drum by the lap joint of the adjoining ring, thus making a layer of steam about in. thick against the shell, which was directly exposed to the hot gases. In the case of vertical or inclined tubes acting as stays to an upper sheet, the upper part of the tubes may become overheated in case of low water; also, when there are stayed sheets, the stays are liable to become corroded.

In addition to these features of design, all boilers are liable to explosion due to corrosion. Internal corrosion is usually due to acid feedwater, and all boilers are equally liable to it. External corrosion, however, is more liable to take place in some designs of boilers than others, and in some locations rather than others. If any portion of a boiler is in a cold and damp place, it is liable to rust out. For this reason the mud-drums of many modern forms of boilers are made of cast iron, which resists rusting better than either wrought iron or steel. If any part of a boiler, other than a part made of cast iron, is liable to be exposed to a cold and damp atmosphere, or covered with damp soot or ashes, or exposed to drip from rain or from leaky pipes, and especially if such part is hidden by brickwork or otherwise so that it cannot be seen, that part is an element of danger.

The causes of boiler explosions may be summarized as follows: (1) Bad materials; (2) bad workmanship; (3) bad water, which eats away the plates by internal corrosion; (4) water lying upon plates, bringing about external