CREAMERY MECHANICS 285 



1. Impure water in the boiler. 



2. Too much water in the boiler. 



3. Too little evaporating surface for the amount of 

 steam used. This is one of the chief objections to upright 

 and too small boilers. 



4. Violent agitation of the water in the boiler caused 

 by too rapid a generation of steam. 



Wet steam causes "priming" and is wasteful of heat. 



Dry Steam. This is saturated steam holding no water 

 mechanically in suspension. High steam pressure and a 

 large steam space above the water level are conducive 

 to dry steam. 



PIORSE POWER OF BOILERS. 



A horse power of a steam boiler is thirty pounds of feed 

 water at a temperature of 100 F. converted into steam 

 in one hour at 76 pounds gauge pressure. 



The horse power of a boiler may be approximately 

 calculated by dividing the total square feet of heating 

 surface in the shell, heads, and tubes, by fifteen. 



SMOKE STACK. 



It is difficult to state the exact size of a smoke stack 

 for a given boiler because conditions vary so much. It 

 is evident that it must be longer for a boiler placed at the 

 foot of a hill than for the same boiler placed on top of 

 the hill. 



A smoke stack for a 25 H. P. boiler should be about 

 one foot square inside and from 30 to 40 feet high and 

 built of brick. A small smoke stack which affords in- 

 adequate draught is wasteful of fuel and gives rise to 

 much trouble in firing. 



