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4s 32 M A R | N Ee Re eB oOM ol om ow ly MAINTENANCE OF MACHINERY IN MERCHANT SHIPS In the Marine Review of Jan. 5 the paper which Mr. Robert Haig, Lloyds' surveyor at Philadelphia, read before the an- nual meeting, was brought up to the point at» which he began the discussion of forced draft. From that point on he stated: "Horced draft--Forced draft has certainly been a most valuable development in engineering, the proof of which need not be presented here; the main question arising in this paper being the effect that forced or accelerated draft has had upon the life and maintenance of boilers. "The two systems to be found in merchant ships are How- den's forced draft and Ellis & Eaves induced draft each of which in competent hands is capable of working the boilers at a very high efficiency. The closed stokehold system has confined itself largely to warships and will not be consid- ered here. "The effect of forced draft upon some boilers has been very marked indeed, and the question is of far-reaching im- portance as to what is the best air pressure to be carried in the ash-pits. In some vessels one-half inch is considered suffi- cient, and is then really an assisted draft, while in others pressures up to about three inches are carried in the ash-pits. It would almost seem as if somewhere between those two ex- tremes would be found the desirable mean, but after close observation I am firmly of opinion that in shell boilers at all events the pressure in the ash-pits should not exceed one inch of water at any time. I have examined many boilers where high air pressures have been in use, and the results have been always the same--buckled and cracked plating, stay nuts - burned off, caulking started, and leaky tubes, whereas, when the air pressure was not allowed to exceed one inch the con- dition of the boilers was as good as those working under nat- ural draft. "The maintenance of boilers under the higher air pressures 'is altogether out of proportion to the extra work got out of them, with the further result that a continuance of these higher pressures will cut out not less than 30 per cent of the useful life of the boiler. The further objection to high air pressures, and it is a potent one, is that there can be no attempt at coal economy with excessive pressures, as experi- ments and trials without number have fully demonstrated. The temptation is keen, to use higher air pressure when mak- ing up time, when coal is bad, or in the endeavor to get a power out of the boilers that their size does not warrant. "These remarks can be applied to water-tube boilers also, although their physical condition is not so seriously affected as the shell boiler; but experience will show that even there a moderate air pressure in point of maintenance and coal con- sumption will be found more than desirable. "Oil fuel--The maintenance of boilers working with oil fuel is, at the present time, of decided interest in view of the possible development in this direction. It is not proposed to deal with the question of oil as a fuel, but rather to con- sider its adaptability and its effect upon boilers. The use of oil fuel has been with a few exceptions confined to oil-carry- ing steamers, but there is not any structural reason to debar its use in ordinary cargo or passenger ships as the fuel can be carried in the double bottom and in tanks fitted in the usual coal bunker spaces. With proper precautions taken the risk of explosion is very remote, as the flash point of the fuel is usually not less than 150° F, "When the fuel is carried in the double bottom a heavy layer of cement three inches thick, properly sectioned off to keep it in place, has proved to be a good insulator for the tank. "The two systems most widely applied to burning oil fuel are compressed air or spraying by steam. "The former requires a small air compressor, or other suitable means for obtaining the required pressure which is usually about one inch; the other method, spraying by steam, requires the installation of extra evaporators to make up the loss of water used in spraying the oil, which is found to be about 3 per cent of the total steam evaporated. With the com- pressed air a certain amount of steam is, of course, required to drive the air compressor, but there is no doubt that with the air heated to a high temperature this process will be found to show a high efficiency, especially in long voyages, as under oil fuel conditions the combustion and the steam are steady, which always means economy. "The condition of the boilers after using oil fuel is found, when the necessary safeguards have been taken to protect the surfaces of the combustion chamber from direct impact with the flame, not to differ to any material extent from that of boilers burning coal. "The combustion chamber backs and sides require to be protected with brickwork carried up above the level of the furnace crown, and in most cases the furnaces are bricked over also, and arrangements of brick arches erected in the furnace to baffle or break up the torch-shaped flame within the length of the furnace. When these conditions are prop- erly carried out, the boilers show not the slightest sign of dis- tress, but if the brickwork is allowed to come down it means that the flame strikes straight through into the chamber; the furnace does comparatively little work, intense heat is local- ized in the combustion chamber back and tube plates, causing serious distortion and leakage. | "I have examined boilers that were less than twelve months in use, where the combustion chambers were seriously dam- aged from neglect to keep the brickwork in good condition. The burning of oil fuel is supposed to be a simple operation, and so it is when we know how to 'do it. "There is every reason why boilers should work well under oil fuel. The temperature of the gases of combustion varies but little; there is no opening of furnace doors, and cleaning fires; the men readily handle it intelligently, and the mainte- nance of boilers working under oil fuel should, in capable hands, be less than under coal conditions. The drawbacks at present to its wider use seems to be more commercial than mechanical. "Superheating--The interest now being taken in the ques- tion of superheat seems to indicate that we have arrived at another period in the cycle of development in engineering. "When steam presstres ranged from 40-lb. to 8o- Ib. superheaters of many types were in general use, and were considered almost indispensable, and at these low pres- sures they certainly were of value; but with the advent of the triple and later the quadruple expansion engines, superheaters went out of use. "The whole aim of engineers for some considerable time past has been to seek for the improved economy in higher steam pressures the quadruple following the triple when pres- sures rose above 180 lbs. per square inch, and later, in the case of the Inchdune and other ships for the same firm, the five-crank engine was developed with Scotch boilers working at a pressure of 267 lbs. per square inch. IMPROVED ECONOMY IN HIGHER STEAM PRESSURES. "Engineers are now convinced that if any further economy is to be reached by higher pressures, a very radical departure will require to be made from the present type of engine and boiler. The times would seem to be propitious for this change, as shadowed forth in the development of the steam turbine and the more general use of water-tube boilers, but even in the turbine it is recognized more fully than in the reciprocating engine that there are great possibilities for. 4 higher efficiency and economy by the use of superheated steam. Dealing with the present reciprocating engine, it is