Railway and Locomotive Engineering . he poten-tial energy of the boiler at a time wlien thelocomotive cylinders cannot develop thefull boiler output, that is at starting andat a comparatively slow speed. It will beseen, therefore, that the economy of thefeed water heater is based not on the satu-rated engine, but on the increased volumeof steam produced by the arch and theaugmented temperature of the steam,which is the product of superheating. Be-low a speed of 25 miles per hour, theincreased capacity shown by Curve D isnot all attributable to the feed waterheater, but is due to the greater po
Railway and Locomotive Engineering . he poten-tial energy of the boiler at a time wlien thelocomotive cylinders cannot develop thefull boiler output, that is at starting andat a comparatively slow speed. It will beseen, therefore, that the economy of thefeed water heater is based not on the satu-rated engine, but on the increased volumeof steam produced by the arch and theaugmented temperature of the steam,which is the product of superheating. Be-low a speed of 25 miles per hour, theincreased capacity shown by Curve D isnot all attributable to the feed waterheater, but is due to the greater potentialcapacity of the boiler, which can only beutilized when a larger cylinder is from this curve there were ob- 25 30 iricreasing factors. The second is afurther development showing the poundsof coal used per indicated horsepowerhour at a wide range of speeds. It illus- foot of grate per hour. Better fuel rateshave been obtained on testing plants wherethe fuel consumption per square foot ofgrate area per hour was trates the relative coal consumption perhorsepower hour of a plain saturated lo-comotive and the same engine equippedwith available power increasing factors. These curves are based on the locomo-tive consuming the same weight of fuelper hour under all conditions of equip-ment and illustrates the fact that the great- June, 1921 RAILWAY AND LOCOMOTIVE ENGINEERING 159 est conservation of fuel can only be ob-tained when advantage is taken of capacityincreasing factors which derive theirpower from a more efficient utilization- ofthe heat units jn the fuel. These curvesrepresent the same engine the UnitedStates Railwav Administration Hght 2-8-2 versed when 45 miles per hour is other words, at all speeds where theengines are likely to damage the track theheavy Mikados with Ught parts are saferengines than the light Mikados with heavyparts. In this comparison, it should beborne in mind that the heavy Mikado has
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