AIR COMPRESSORS 101 



and dried. It is then dipped in warm enamel to coat both 

 inside and outside surfaces, and baked at a high temperature, 

 the dipping and baking operations being repeated to give a 

 second coat. The mark )0(f just above the pipe tap in the 

 head of a reservoir indicates enamel reservoir. The mark )@( 

 indicates plain reservoir. 



Location of Reservoirs. It is strongly recommended that 

 the main-reservoir capacity be divided into two reservoirs of 

 suitable dimensions, so located and so connected by piping, 

 as to give the greatest possible radiating surface to cool 

 the air to atmospheric temperature, and cause the precipi- 

 tation of as much moisture as possible before the air is 

 drawn out of the reservoir. Main reservoirs should be located 

 in as cool a position as possible and never at the side of the 

 firebox. 



The standard sizes of main reservoirs are designed for a 

 maximum pressure of 140 lb.; special reservoirs built to carry 

 more than 140 lb. can be obtained on special specifications. 



Calculating Main-Reservoir Capacity. To find the capacity 

 of a main reservoir, apply the following rule: 



Rule. To calculate the approximate capacity of a reservoir, 

 in cubic inches, multiply its cross-sectional area, in square 

 inches, by the inside length, in inches. 



EXAMPLE 1. What is the capacity of a reservoir 18 in. in 

 diameter and 100 in. in length (inside measurements)? 



SOLUTION. The cross-sectional area of the reservoir is 

 20 X 20 X. 7854 = 314. 16 sq. in. The length is 100 in. There- 

 fore, the capacity is 314.16X100 = 31,416 cu. in. 



To calculate approximately the capacity of a main reservoir 

 from its outside dimensions, subtract \ in. from its diameter 

 and 3 in. from its length, so as to reduce the outside measure- 

 ments to inside measurements; then proceed as before. The 

 J in. from the diameter allows for the thicknesses of metal in 

 the walls, while the 3 in. from the length allows for the thick- 

 ness of metal of the ends and for the way the ends are secured 

 in place. 



EXAMPLE 2. What is the capacity of a main reservoir 

 26i in. in diameter by 96 in. long? 



