the number of boilers in service is held at that which will most efficiently carry the load. (Refer to schedule for boiler operation.) He must make frequent visits to the boiler room and at such times always observe the condition of the fires and examine the records of the various recording gauges in the fireroom (steam-pressure gauge, flow meters, feed-water thermometers, and CO, recorders), with a view to determining conditions of operation since the previous round, making such corrections as may be necessary. He must further be present whenever a boiler is blown down, and must see that all banking, cutting in, and cutting out of boilers is done without unnecessary waste of fuel and in accordance with instructions prescribed. Except as required in emergency, any boiler which it is desired to cut out for overhaul, repair, or cleaning must be cut out at a time when the load on the plant falls sufficiently to permit of sparing the services of that boiler. Correspondingly, boilers which it is desired to cut in must, except in cases of emergency, be fired up during the night and cut in as they are required in the morning.

21-51. Flue gas content. Bolier-room operatives must at all times give especial attention to the per cent CO, as indicated by the gauges in the fireroom, and should use every effort to maintain this as nearly at 14 per cent as possible. The cause of any fluctuations from this point must be investigated at once and remedied as promptly as possible, either by a more careful stoking (see instructions on operation of stokers in another part of this chapter), or by an adjustment of the dampers on the individual boilers.

21-52. Damper position. The movement of the damper position indicator, except as affected by a sudden marked fluctuation in load, affords a most reliable and sensitive guide to the condition of fires. With boilers operated in accordance with schedule prescribed, there is a correct range for damper position. This range must be determined by the engineer in charge, and instructions shall be issued to the firemen that movement of the position indicator beyond the range established indicates improper condition of the fires, which must be ascertained and remedied at once.

21-53. Fireroom cleaning. The operatives employed for coal and ash handling are to be responsible for the general cleanliness of boiler room, boiler tops and settings, and economizer tops and settings. The work in connection with coal and ash handling should be completed at as early an hour as possible in order to allow time.

for other duties. Whenever practicable, coal bunkers should be filled first each day, after which ashes should be removed and other duties in connection with coal and ash handling plant maintenance performed.

21-54. Ash removal. Where ash hoppers are not provided it should be the duty of the firemen to draw the ashes from the ash pits as soon as dumped, to prevent reduction of draft and warping of grate bars. During evening and night watches the refuse ashes should be handled entirely by the firemen on watch.

21-55. Cleaning of boilers. All boilers must be shut down for external cleaning and inspection of furnace and grates after not more than 720 hours of steaming as a maximum, exclusive of time fires are banked, and at this time must receive thorough cleaning of fire side of tubes, etc.; removal of soot from combustion chamber; cleaning out and repair of furnace and grate; repair of setting and baffles; examination and overhaul of blow-off valves, as required; and overhaul of water columns. Under the personal supervision of the engineer in charge, observation shall be made to determine the rate of deposit of scale. As the result of these observations a schedule shall be prepared to govern the frequency of internal cleaning. Such cleaning should be done only at such intervals as will insure efficient operation. Ordinarily the cleaning will be required more frequently for the lower rows of tubes than for the remainder of the boiler. The character and extent of the scale formation must be under constant observation in order that the schedule may be modified to meet the changing requirements due to variation in the quality of the feed water. The periodical internal cleaning must be thorough and complete in every particular.

21-56. All boilers out of service for internal cleaning should receive thorough internal and external cleaning and careful examination for deterioration; overhaul of stop valves, feed valves, blow-off valves, and of safety valves; adjustment of steam gauge and inspection of safety fusible plugs, if provided; and, upon returning to service, adjustment of safety valve. Whenever a boiler or any other piece of important apparatus is taken out of service for any cause, the effort should be made to complete promptly any work which may be required upon it.

21-57. All boilers shall be inspected quarterly, and reports submitted on Y&D form 91 to the Chief of the Bureau of Yards and

Docks, as required by article 1532-6, Navy Regulations. Intermediate periodical inspection should be made as frequently as practicable, and necessary action taken to insure that the boilers are in best practicable operating condition. The heating surfaces must be free from soot, scale, dust, and oil. In water-tube boilers straight tubes shall be tested with straight edge to detect blisters, bulging, or excessive deflection. Blistered or bulged tubes and tubes exhibiting a deflection exceeding three-fourths inch should be renewed. Steam tube cleaners, where installed, shall always be operated before a fire is permitted to die out. All auxiliary and minor equipment must also be in good condition.

21-58. When a boiler is taken out of service, all ashes and soot should be removed from boiler and setting. If the boiler is not to be returned to service within a month, precautions shall be taken to prevent corrosion, preferably by spraying fire side of tubes with fuel. oil, or by providing small fires in pans or stoves inside the boiler settings to dry up moisture in the atmosphere; the latter requirement is particularly desirable in wet weather. The water space of the boiler should be drained, a pan of liberal size half full of dehydrated lime inserted, and the boiler effectively sealed. The lime should be inspected, and renewed if necessary, at least once a month during the first three months, and quarterly thereafter.

21-59. Hydrostatic test. At least once annually, or more frequently if necessary, boilers shall be subjected to a hydrostatic test pressure of one and one-half times the working pressure. The hydrostatic test pressure should be maintained in the boiler for a sufficient length of time to permit inspection for leaks. During the hydrostatic test the safety valve or valves shall be removed and the opening blanked off; or each valve disk shall be held to its seat by means of a testing clamp (and not by screwing down the compression screw upon the spring).

21-60. Dusting tubes. In order that the boilers may be operated most efficiently, it is essential that the heating surfaces be kept thoroughly cleaned. The engineer must see that the tubes on every boiler, either in service or banked, are thoroughly dusted daily-this work being done by the fireman on watch. Whenever possible this work is to be done with compressed air, but steam should be used in case air connections are not conveniently obtainable. If compressed air is used for dusting, it should be discharged of all water or water

vapor from the supply line before operating the soot blowers. Where automatic steam soot-blower equipment is installed on the boilers, tubes should be dusted every watch; and care must be taken that all parts operate effectively to remove the soot thoroughly, and that the valves and connections do not leak steam. In connecting steam pipe care must also be exercised to avoid a pocket for the accumulation of condensed steam, which when discharged against dirty boiler tubes does more damage than the soot it is intended to remove.

21-61. Boiler feed water; danger from contained oil. Waters containing carbonates and sulphates of magnesia and lime, soluble salts of silica, iron and alumina and suspended matter tend to form scale in the boiler and reduce steam generating capacity and economy. Waters containing acids, organic matter, and magnesium chloride and magnesium sulphate tend to corrode the boiler. Those containing sodium carbonate, organic matter, and alkalies induce priming. The two most common modes of chemical treatment for water are by use of boiler compounds and purifying plants. In the former the chemical action takes place inside the boiler; in the latter the water is purified before it enters the boiler. The object of treatment with compounds is to neutralize the evil effect of the impurities or to change them into others which are less objectionable and are easily removed. Oil in the feed water is a source of danger which should be habitually guarded against. Examination of the feed water should be made at intervals sufficiently frequent to insure that oil is not contained therein.

21-62. Compounds for boiler feed water shall not be used except by specific authority from the Chief of the Bureau of Yards and Docks, and then only in the quantities authorized. In many cases these preparations are of benefit, but when improperly used they may produce more deleterious effects than the impurities they are intended to eliminate. Compounds may be divided into three classes, as follows: (a) Those converting scale-forming elements into new substances easily removed; (b) those enveloping the precipitated scale-forming crystals, and preventing them from cementing together; (c) those preventing, by a physical action, the formation of a hard scale. The use of boiler compounds does not necessarily prevent scale from forming, it being intended merely to reduce the evil and facilitate removal of scale when deposited. Boiler compounds should be introduced continuously or intermittently at short intervals.

21-63. Continuous feeding of solution may be accomplished by connecting the suction side of the feed pump with a solution reservoir, its action being similar to an ordinary cylinder-oil lubricator. Intermittent feeding may be obtained by connecting the suction pipe leading to feed pump with a solution reservoir and controlling the solution fed by means of valve.

21-64. Analysis of feed water desirable. Where observation indicates the deposit of objectionable scale, an analysis of the feed water should be obtained, if practicable, and forwarded to the bureau for consideration. If impracticable to obtain an analysis, a sample of feed water, approximately 3 gallons, should be forwarded to the bureau.

21-65. Where there is a corrosive action in the boilers because of the presence of acid in the water or of oil containing fatty acids, which will decompose and cause pitting wherever the sludge can find a resting place, such action may be overcome by the neutralization of the water by means of carbonate of soda. Such neutralization should be carried to the point where the water, as extracted from the water column, will just turn red litmus paper blue. Entrained air in feed water is very corrosive. Where feed-water heaters of the open type are used, little trouble should be experienced from this source; with the closed type, however, automatic air vents should be installed to relieve the feed-water system of air.

21-66. Silt-bearing feed water. Where feed water is of a siltbearing character, sand and gravel filters are installed to remove the suspended impurities. The filters contain a bed of special washed and graded silica sand of high purity, superimposed upon layers of carefully washed and graded gravel. The water enters the filter at the top and passes down through the sand and gravel filter bed and out at the bottom. The sediment or suspended matter which is removed from the water collects on the top of the filter bed, which should be periodically cleaned by washing with a reverse flow of water. The washed water in this case enters the filter at the bottom and is distributed evenly to all parts of the filter bed through the collector system in the bottom. It passes up through the filter bed and discharges through openings on the top, carrying the sediment or suspended matter out through the waste valve.

21-67. Blowing down water-tube boilers. The mud drums of all boilers in service or banked should be blown down in the