EXAMPLE 2.-What is the factor of evaporation when the feedwater temperature is 122° F. and the gauge pressure 72?

SOLUTION. In the table, under the column headed 70 and opposite 120 in the left-hand column is found 1.128; in column headed 80 and opposite 120 is found 1.131; difference is .003. In the same vertical columns and opposite 130 are found 1.117 and 1.120; difference is .003, same as before. Hence, for an increase of 10 lb. in gauge reading, there is an increase of .003 in the factor of evaporation, or an increase of .0003 for 1 lb. and of .0003X2=.0006 for 2 lb. Therefore, for a feedwater temperature of 120° and 72 lb. pressure, the factor of evaporation is 1.128+.0006=1.1286. The difference between the numbers opposite 120 and 130 in the two columns headed 70 and 80, respectively, is 1.128-1.117.011, and 1.31-1.120.011, showing that, for an increase of temperature in the feedwater of 10°, there is a decrease in the factor of .011 and for 1° a decrease of .0011, or for 2° of .0022. Hence, the value of the factor for a temperature of 122° and a gauge pressure of 72 lb. is 1.1286-.0022 = 1.126.

Boiler Efficiency.-The efficiency of a boiler may be defined as the ratio of the heat utilized in evaporating water to the total heat supplied by the fuel. The efficiency thus calculated is really the combined efficiency of the furnace and boiler, as it is not easily possible to determine separately the efficiency of each. The amount of heat supplied is determined by first accurately weighing the fuel used during the test and deducting all the ash and unconsumed portions. This weight, in pounds, is multiplied by the total heat of combustion of 1 lb. of the fuel, as determined by an analysis, the product being the total number of heat units supplied during the test under the assumption that combustion was perfect. The heat usefully expended in evaporating water is obtained by first weighing the feedwater and correcting this weight according to the quality of the steam; the corrected weight is then multiplied by the number of heat units required to change water at the temperature of the feed into steam at the observed pressure. The efficiency of the boiler, expressed as a per cent., may be found by the formula

in which

E=

A
B'

A heat utilized in evaporating water;

B=total heat supplied by fuel.

EXAMPLE.-A boiler trial shows a useful expenditure of 186,429,030 B. T. U. and a total supply of 270,187,000 B. T. U. What is the efficiency of the boiler?

Standard Code. For elaborate boiler trials, the standard code recommended by the American Society of Mechanical Engineers should be used.

BOILER MANAGEMENT

FILLING BOILERS

Preparation for Filling Boiler. Before starting the flow of water into the boiler, the manhole plates or handhole plates that were removed preparatory to cleaning and overhauling must be replaced, and the blow-off valve must be closed. The gaskets, and also the surfaces with which they come in contact, should be examined to see that they are in good condition. It is customary to place a mixture of cylinder oil and graphite on the outer surface of each gasket, so that it may be removed without tearing. It is important that the manhole plates and handhole plates be properly replaced and secured in order to prevent leakage.

Height of Water.-In some cases the water can flow in and fill the boiler to the required height by means of the pressure that exists in the main supply pipe. In other cases, it may be necessary to use a hose or to fill the boiler with a steam pump or a hand pump. The boiler should be filled until the water shows half way up in the gauge glass.

Escape of Air.-While filling a boiler it is necessary to make provision for the escape of the contained air, as otherwise the pressure caused by the compression of the air may prevent the boiler from being filled to the proper height.

Some

Most boilers have some valve that can be used for this purpose; a gauge-cock may be left open until water issues therefrom, when it may be closed. times the manhole plate, if the manhole is on top, is left off while filling a boiler.

MANAGEMENT OF FIRES WHEN STARTING

Precautions in Starting. After the boiler has been filled and before starting the fire, the attendant should see that the water column and connections are perfectly clear and free, that is, that the valves in the connections and the gauge-glass valves are open so that the water level may show in the glass; he should also see that the gauge-cocks are in good working order and should open the top cock or the safety valve; he should take care that the stress on the stop-valve spindle is relieved by just unscrewing the valve from the seat without actually opening it. He should make sure that the pump, or injector, or whatever device is used to feed the boiler, is in good working order, and ready to start when required.

Starting the Fires. It is customary to cover the grates with a layer of coal first, and then to add the wood, among which may be thrown oily waste or other combustible material that may be at hand. To start the fire, light the waste or other easily ignited material and open the damper and ashpit doors to produce draft. Then close the furnace door. After the wood has started to burn well, spread it evenly over the grate and add a fine sprinkling of coal, until this in turn begins to glow, when more coal may be added and the fire occasionally leveled until the proper thickness of fuel has been obtained. Should the chimney refuse to draw, the draft can generally be started by building a small fire in the base of the chimney.

Value of Slow Fires.-When getting up steam, the fire should not be forced but, instead, should be allowed to burn up gradually. By forcing the fire, the plates or tubes that are nearest the fire suffer extreme expansion, while those parts that are remote from the fire are still cold; under such conditions the seams and rivets, and also the tube ends, which are expanded into the tube plates, are liable to be severely strained, and, possibly, permanently injured. It is not desirable to raise steam in any boiler, except in steam fire-engines, in less than from 2 to 4 hr., according to the size, from the time the fire is first started. When steam begins to issue from the opened top gauge-cock or the raised safety valve, as the case may be, the cock or the valve may be closed and the pressure still allowed to rise slowly until the desired pressure has been reached.

Trying the Fittings.-After the pressure at which the boiler is to run has been reached, and before cutting it into service, all the valves and cocks should be tried. The safety valve should be raised and its action noted; the water column should be blown out and the gauge-cocks tested; the feeding apparatus should be tried; and it should be noted particularly whether the check-valves seat properly and the valve in the feedpipe is open. All the accessible parts should be examined for leaks.

CONNECTING BOILERS

Cutting Boiler Into Service.-Cutting a boiler into service is accomplished by opening the stop-valve, thus permitting the steam to flow to the engine or other destination. The stop-valve should be opened very slowly to prevent a too sudden change in the temperature and consequent expansion of the piping through which the steam flows, and also to prevent water hammer. The steampipe drain should be kept open until the pipe is thoroughly warmed up. large plants with many boilers and long steam mains, it takes several hours to warm these pipes thoroughly by the slow circulation of the steam, but the main stop-valve should not be fully opened until these pipes are warm.

In

Connecting Boilers to Main.-Before connecting the different boilers of a battery to the same steam main, the precaution of equalizing the pressures in the different boilers must be observed in order to prevent a sudden rush of steam from one boiler to another. All the pressures should be within about 2 lb. before an attempt is made to connect the boilers.

Changing Over.-In plants where there are duplicate sets of boilers, one set being in operation while the other is undergoing repairs, overhauling, and cleaning, the method of changing over, or connecting, is as follows: Start the fires and raise steam in the boilers that are to be cut into service. Allow the pressure to rise in all to within 5 lb. of that which is in the boilers in operation. All arrangements before changing over should be made with a view of getting all the heat that can be obtained from the fires in the boilers that are to be cut

out. This can be accomplished by running until the fires have given up all their available heat for making steam, as indicated by the gradual fall in pressure when the dampers are wide open, and then making the change. While the fires in one set of boilers are burning low and the pressure is falling, the pressure in the boilers to be cut in is gradually rising and meeting, so to speak, the falling pressure of the set in operation. When the difference of 5 lb. is reached, change over. A man should be stationed at each stop-valve, and while one is being opened the other should be closed; the engine will continue running uninterruptedly while the change is being made.

EQUALIZING THE FEED

When the boilers of a battery have been cut into service and hence are all connected together through the steam main, the regulation and equalization of the feed water becomes an important factor. Each boiler has its own checkvalve and feed stop-valve, and generally all the boilers are supplied from one pump, which is running constantly. The quantity of water admitted to each boiler is regulated by its feed stop-valve. When the water gets low in any boiler the feed stop-valve should be opened wider, while at the same time the feed stop-valves on one or more of the other boilers in operation may be closed partly and thus divert the feedwater to the one most requiring it. Some boiler plants have check-valves with an adjustable lift; in that case the feed is equalized by adjusting the lifts of the check-valves, the stop-valves being left wide open while running. It will be understood from the foregoing that the object in view is the maintaining of an equal water level in all the boilers through the manipulation of the feed stop-valves or check-valves. A boiler that is not doing its legitimate share in generating steam may be known by the fact that the feed stop-valve or check-valve on that boiler will be nearly, if not entirely, closed most of the time.

FIRING WITH SOLID FUEL

The safe and economical operation of steam boilers calls for careful and intelligent management. The fires should be kept in such condition as to maintain the desired pressure and to burn the fuel with economy. Different fuels require different handling and hence only general rules can be given; much will depend on the skill and judgment of the attendant, who must himself discover in each case by actual trial the best method to pursue. The fires must be cleaned at intervals; the time and method of cleaning depend on the nature of the fuel and the rapidity with which it is being consumed, the style of grate in use, and the construction of the furnace.

Cleaning of Fires.-There are two methods employed in cleaning the fires: first, that of cleaning the front half and then the rear half; second, that of cleaning one side of the fire and then the other side. In the first method, previous to cleaning, green fuel is thrown on and allowed to burn partly until it glows over the entire surface. The new and glowing fuel is then pushed to the back of the furnace with a hoe, leaving nothing on the front half of the grate but the ashes and clinkers, which are then pulled out, leaving the front end of the grate entirely bare. The new fire, which was pushed back, is drawn forwards and spread over the bare half of the grate. The ashes and clinkers that are on the rear half of the grate are then pulled over the top of the front half of the fire and out through the furnace door; this leaves the rear half of the grate bare, which must be covered by pushing back some of the new front fire. The clean fire having been spread evenly, some new fuel must be spread over the entire surface.

The second method is substantially the same in principle, but the fire is pushed to one side instead of to one end of the furnace. The condition of the fires themselves and the nature of the service of the plant will determine just how often and at what time the cleaning of fires should take place. In general, the fires in stationary boilers require cleaning at intervals of from 8 to 12 hr. Fires require cleaning more often when forced draft is used than when working with natural draft.

Rapidity in cleaning fires is of great importance, as during the operation a large volume of cold air enters the furnace and chills the metallic surfaces with which it comes in contact; consequently, the boiler is damaged, however slightly. It is the greatest advantage of shaking grates that they allow the fire to be cleaned without opening the furnace door; the inrush of cold air and consequent chilling of the plates, etc. is thus avoided.

Before starting to clean fires, the steam pressure and the water level should be run up as high as is safe and the feed should be shut off in order to reduce

the loss in pressure while cleaning. The condition of the fire during cleaning and the opening of the furnace doors cause the pressure to drop quite rapidly, but the rapidity and the amount of drop will be reduced by taking the precautions mentioned and cleaning quickly.

The amount of drop in pressure while cleaning fires depends on several conditions. For example, with a boiler that has a small steam space and, in addition, is too small for the work required of it without forcing, it is to be expected that the drop in pressure will be much more than if the reverse conditions exist. Furthermore, it may be necessary to clean fires while steam is being drawn from the boiler, instead of being able to clean at a time when the engine is stopped. In that case a greater drop must be expected than when cleaning while no steam is being drawn from the boiler. It is advisable when possible to do the cleaning at a time when no steam is being drawn from the boiler or when the demand for steam is light.

UNIFORM STEAM PRESSURE

Desirability of Uniform Pressure.-The attendant should aim to carry the pressure in the boiler as uniform as possible. A steady steam pressure and a steady water level are conducive to economy in the use of a fuel because, with these conditions, in a properly designed plant there will be a fairly steady temperature in the furnace, which, under normal conditions, is sufficiently high to insure a thorough ignition of the volatile matter in the coal. With a constant demand for steam, a fluctuation in the steam pressure is caused by a change in the furnace temperature, assuming the feedwater supply to be constant, and whenever the steam pressure is down, the furnace temperature is low at the same time. In consequence of this, large quantities of the volatile matter in the coal often escape unconsumed and cause a serious loss of heat. Furthermore, with a steady steam pressure the stresses on the boiler are constant, and hence the life of the boiler will be increased and repair bills will be smaller than otherwise.

Maintenance of Uniform Pressure. During the period of time between the cleaning of the fires, the pressure may be carried nearly uniform by manipulating the feed apparatus so that just the necessary amount of water constantly enters the boiler. Intermittent feeding is practiced under certain local conditions, as, for example, where there is an injector or a pump that is so large that it is impossible to run it continuously without increasing the height of the water level. In such a case, the feeding must be stopped just before firing, and is not resumed until the new fire begins to make steam, as indicated by the rise of pressure on the gauge. If the pressure tends to rise above the standard or normal the dampers must be partly closed and the quantity of feed increased, assuming in this case that no damper regulator is fitted and that, hence, the damper is regulated by hand. A damper regulator, systematic firing, and proper feeding are essential for carrying a practically uniform pressure. Should the pressure continue to rise, more green fuel must be thrown on, the damper closed, the feed increased, and only as a last resort should the furnace door be opened.

A uniform steam pressure cannot be kept without proper firing. To maintain such a pressure the following directions should be observed: Keep the fire uniformly thick; allow no air holes in the bed of fuel; fire evenly and regularly; be careful not to fire too much at a time; keep the fire free from ashes and clinkers; and do not neglect the sides and corners while keeping the center clean. Do not, however, clean the fires oftener than is necessary. Keep the ash-pit clear.

Keeping Water Level Constant.-In connection with the maintenance of a constant water level, the following instructions should be followed: On starting to work, remember that the first duty of the fireman is to examine the water level. Try the gauge-cocks, as the gauge glass is not always reliable. If there is a battery of boilers, try the gauge-cocks on each boiler.

PRIMING AND FOAMING

Priming. The phenomenon called priming is analogous to boiling over; the water is carried into the steam pipes and thence to the engine, where considerable damage is liable to take place if the trouble is not checked in time. There are several causes for priming, the most common ones of which are: insufficient boiler power, defective design of boiler, water level carried too high, irregular firing, and sudden opening of stop-valves.

When the boiler power is insufficient, the best remedy is to increase the boiler plant; the next best thing to do is to put in a separator, which, obviously,

will only prevent the entrained water from reaching the engine, and will not stop the priming.

Defective design of a boiler generally consists of a steam space that is too small or a bad arrangement of the tubes, which may be spaced so close in an effort to obtain a large heating surface as to interfere seriously with the circulation. In horizontal return-tubular boilers, a sufficiently large steam space can be obtained by the addition of a steam drum; sometimes the top row of tubes can be taken out to advantage, which permits a lower water level. Defective circulation in horizontal fire-tube boilers is difficult to detect and to remedy; if it is due to a too close spacing of the tubes, a marked betterment may be effected by the removal of one or two vertical rows of tubes. The remedy for a water level that is too high is to carry the water at a lower level.

Evidences of Priming.-Priming manifests itself first by a peculiar clicking sound in the cylinder of the engine, due to water thrown against the heads. In cases of very violent priming, the water will suddenly rise several inches in the gauge glass, thus showing more water in the boiler than there really is. When priming takes place, it can be checked temporarily as follows: Close the damper, and thereby check the fires until the water is quiet; the engine stop-valve should also be partly closed to check the inrush of water. Observe whether the water drops in the gauge glass, and then, if more feed is needed, increase the feed. To prevent damage to the engine, open the cylinder drains. Regular and even firing tends to prevent priming.

Foaming.-The phenomenon called foaming is not the same as priming, though frequently considered so. Foaming is the result of dirty or greasy water in the boiler; the water foams and froths at the surface, but does not lift. A boiler may prime and foam simultaneously, but a foaming boiler does not always prime. Foaming while taking place is visible in the gauge glass and is best remedied by using the surface blow-off. If no surface blow-off is fitted, the bottom blow-off may be used in order to get rid of the dirty water. Like priming, foaming will cause a wrong level to be shown, and hence the first thing to do in case of foaming is to quiet the water by checking the outrush of steam, either by slowing the engine down or by checking the fire, or by both.

SHUTTING DOWN AND STARTING UP

Preparations for Shutting Down. Before shutting down for the night it is advisable to fill the boiler to the top of the glass, so as to be sure to have sufficient water to start with in the morning. The presence of possible leaks through the valves, tube ends, or seams necessitates this course of action. Even if no leaks exist, it is good practice to do this, if for no other reason than to admit of blowing out a portion before raising steam in the morning. All the gauge-cocks should be tried and the water column should be blown out to insure their being free and clear.

Banking of Fires.-The fires may be banked at such a time that there will be about enough steam to finish the day's run, thus shutting down under a reduced pressure with only a remote possibility of its rising again through the night. If the fires are properly banked and the steam worked off while the feed is on, it will be remotely possible for the pressure to rise during the night to a dangerous extent. To bank the fires they should be shoved to the back of the grate and well covered with green fuel, leaving the front part of the grate bare, thus preventing any possibility of the banked fire burning up through the night.

Closing Valves and Damper. The steam stop-valve, feed stop-valve, whistle valve, and other steam valves should be closed; the valves at the top and bottom of the gauge glass also should be shut off to prevent loss of water, etc. in case the glass should break during the night. If there is a damper regulator, it should be so arranged that the damper may be left closed, but not quite tight, because a small opening must be left to permit the collecting gases from the banked fire to escape up the chimney; otherwise, there is danger that the gas will ignite and cause an explosion. It is very important to take this precaution and also to make a mark by means of which the distance the damper is open can be ascertained at a glance. In fact, a damper should be so made that when shut to the full extent of its travel there will be still sufficient space around it to allow the gas to escape. The damper regulator should be rendered positively inoperative in any manner permitted by its design so that when closed it will remain in that position until connected properly by the attendant in the morning.

Starting the Fires.-On entering the boiler room in the morning, the quantity of water in the boiler should first be noted. The gauge glass and the