28 BULLETIN 747, U. S. DEPARTMENT OF AGEICULffTJEE. 



the inside and outside of pipe. Suppose there is an equivalent of 50 



square feet of steam piping in the average creamery and the steam 



pressure carried in the piping is 70 pounds' gauge, and the average 



room temperature is 70° F. (The temperature of the steam inside 



the pipe when at a pressure of 70 pounds' gauge is 316° F.) ; then the 



loss per hour is 50X3(316— 70) =36,900 B. t.. u. If the plant is 



operated 8 hours a day for 300 daj^s in a year the loss will be 36,900 X 



8X300=88,560,000 B. t. u. With a boiler and furnace efficiency of 



50 per cent and coal containing' 12,500 B. t. u. per pound it would 



• ,, i p 88,560,000 



require the burning of i o 500 y 50 =14,009 pounds, or about 7 short 



tons, which at $5 a ton would amount to $35* annually. Good insula- 

 tion will reduce this loss about 85 per cent, in which case the loss 

 would be only $5.25, which would mean an annual saving of $29.75. 

 The cost of the insulation put on the pipes should not exceed 50 cents 

 a square foot, making the cost of insulating the piping* 50X-50=$25. 

 The insulation, therefore, will more than pay for itself through the 

 saving of fuel in one year. 



SELECTION OF POWER. 



The accepted boiler horsepower is the" evaporating of 34.5 pounds 

 of water an hour from- a feed-water temperature of 212° F. into 

 steam at the same temperature, corresponding to atmospheric pres- 

 sure. This is equivalent to the absorption of 34.5X970.4=33,478.8 

 B. t. u. There is, therefore, no direct connection between the horse- 

 power rating of a boiler and that of a steam engine or other steam- 

 driven machine. For instance, the latest and most improved triple- 

 expansion engines condensing with high-pressure steam have pro- 

 duced a horsepower hour on about 9 pounds of steam, whereas the 

 ordinary small slide-valve engine commonly employed in the smaller 

 dairy establishments will use anywhere from 40 to 80 pounds of steam 

 per horsepower hour. One boiler horsepower when used in connec- 

 tion with the most improved engines will furnish sufficient steam to 

 produce nearly four horsepower hours, but if used in the smaller 

 engines may produce only about one-half of a horsepower hour. 

 Consequently, in estimating the size of boiler necessary the steam 

 consumption of the engine and auxiliaries must be taken into consid- 

 eration. For example, a 12-horsepower engine of the type generally 

 used in the smaller creameries requires at full load about 60 pounds 

 of steam per horsepower per hour at a gauge pressure of 70 pounds, 

 or 12X60=720 pounds. The horsepower capacity of the boiler to 



720 

 supply steam will be 2k =20.8. But this is assuming that the feed 



water is fed to the boiler at a temperature of 212° F., or at the boil- 



