The figures that have been given refer to the possible saving through the use 

 of superheated steam in the prime movers alone. Where the auxiliaries are of a 

 design that can properly handle superheated steam there will be a larger percent- 

 age of gain than in the prime movers. This is due to the fact that it is the 

 auxiliaries in a plant that ordinarily show the lowest economy and the lower 

 the efficiency of the steam apparatus, the greater the saving possible. 



An example from actual practice will perhaps best illustrate and emphasize 

 the foregoing facts. In October, 1909, a series of comparable tests were 

 conducted by The Babcock & Wilcox Co. on the steam yacht " Idalia " to 

 determine the steam consumption both with saturated and superheated steam of 

 the main engine on that yacht, including as well the feed pump, circulating pump 

 and air pump. These tests are more representative than are most tests of like 

 character in that the saving in the steam consumption of the auxiliaries, which 

 were much more wasteful than the main engine, formed an important factor. A 

 resume of these tests was published in the Journal of the Society of Naval 

 Engineers, November, 1909. 



The main engine of the " Idalia " is four cylinder, triple expansion 

 11^x19x22^x18 inches stroke. Steam is supplied by a Babcock & Wilcox 

 marine boiler having 2500 square feet of boiler heating surface, 340 square feet 

 of superheating surface and 65 square feet of grate surface. 



The auxiliaries consist of a feed pump 6x4x6 inches, an independent air 

 pump 6x12x8 inches, and a centrifugal pump driven by a reciprocating engine 

 5/3 x 5 inches. Under ordinary operating conditions the superheat existing is 

 about TOO degrees Fahrenheit. 



Tests were made with various degrees of superheat, the amount being 

 varied by by -passing the gases, and in the tests with the lower amounts of 

 superheat by passing a portion of the steam from the boiler to the steam main 

 without passing it through the superheater. Steam temperature readings were 

 taken at the engine throttle. In the tests with saturated steam, the superheater 

 was completely cut out of the system. Careful calorimeter measurements 

 were taken, showing that the saturated steam delivered to the superheater 

 was dry. 



The weight of steam used was determined from the weight of the condensed 

 steam discharged from the surface condenser, the water being pumped from the 

 hot well into a tank mounted on platform scales. The same indicators, ther- 

 mometers and gauges were used in all the tests so that the results are directly 

 comparable. The indicators used were of the outside spring type so that there 

 was no effect of the temperature of the steam. All tests were of sufficient 

 duration to show a uniformity of results by hours. A summary of the results 

 secured is given in Table 2, which shows the water rate per indicated horse 

 power and the heat consumption. The latter figures are computed on the basis 

 of the heat imparted to the steam above the actual temperature of the feed water, 

 and, as stated, these are the figures that are directly comparable. 



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