30 BULLETIN 1i% U. S. DEPARTMENT OF AGRICULTURE. 



live steam from the boiler and the boiler capacity can be reduced 

 practically one-half with a corresponding reduction in fuel, to say 

 nothing of the lessened strain placed on the- boiler -through forcing 

 and the extra labor required in firing. By feeding the boiler with 

 water heated by exhaust steam, expansion and contraction strains are 

 greatly lessened, the fuel consumption is reduced as well as the work 

 of firing, and the capacity of the boiler is increased in proportion to 

 the temperature to which the feed water is heated. Where there is 

 use for the heat in the exhaust steam from the engine, pumps, and 

 other steam-driven machinery the power developed becomes' a by- 

 product of the heating system, and hence costs but little. In a milk 

 plant or creamery in which pasteurization is practiced steam power 

 is, generally speaking, "the cheapest, for it is necessary to provide a 

 boiler to furnish steam for the pasteurizing* and as there is about 85 

 per cent of the heat in live steam at 70 pounds 7 gauge pressure remain- 

 ing in the exhaust steam from the engine, it is economy to use the 

 steam first in the engine to produce the required power for oper- 

 ating the machinery and then for the purpose of pasteurizing, heat- 

 ing water, and heating the building. 



The size of boiler will be approximately the same whether it is 

 used for pasteurizing onty or for furnishing steam first to the engine 

 and then employing the exhaust steam in the pasteurizer. Especially 

 is this true if the engine is operated only a few hours daily, as it is 

 necessary to raise steam for pasteurizing and after the boiler is once 

 fired up but little additional fuel is required to furnish steam for 

 power purposes for, say, three or four hours. 



There are certain conditions, however, in which it is more eco- 

 nomical to install a boiler for heating and a gas engine or electric 

 motor for power. For instance, in nonpasteurizing plants where 

 only a comparatively small quantity of heat is required for heating 

 the wash water, a small boiler may be used for generating low-pres- 

 sure steam for heating, and a gas engine or electric motor for run- 

 ning the machinery. The advantages in employing a gas engine or 

 electric motor are that it is ready for instant use and that power 

 costs cease with the stopping of the machine. With a steam-engine, 

 however, time is required to raise steam in the boiler and firing must 

 be continued while the engine is in use. Furthermore, it requires 

 about 10 pounds of coal per horsepower capacity of the boiler for 

 raising steam. That is, a 20-horsepower boiler requires about 200 

 pounds of coal for heating the walls of the setting and raising steam 

 to a pressure of 70 pounds' gauge pressure. In some oases the appa- 

 ratus requiring power is operated intermittently throughout the 

 day, in which case it may not be advisable to use a steam engine, as 



