100 STEAM 



weight of the entering steam per cubic foot, different values 

 of d may be assumed, until a value is found that will give the 

 necessary discharge W. This is the required pipe diameter. 



The approximate weights of steam delivered per minute 

 through 100 ft. of pipe of various diameters, with a drop of 

 pressure of 1 lb., are given in the accompanying table. On 

 the whole, these values are slightly higher than those which 

 would be obtained by the foregoing formula for the same con- 

 ditions. If the drop of pressure is more or less than 1 lb., the 

 value in the table must be multiplied by the square root of the 

 drop, to obtain the discharge. Also, if the length of the pipe is 

 more or less than 100 ft., divide 100 by the length, in feet, and 

 multiply the square root of this quotient by the value given 

 in the table. The following example illustrates this point. 



EXAMPLE. How many pounds of steam will be discharged 

 per minute, with an initial gauge pressure of 120 lb. per sq. in., 

 through a pipe 3 in. in diameter and 400 ft. long, with a drop of 

 pressure of 2 lb. ? 



SOLUTION. From the table, the amount discharged through 

 100 ft. of 3-in. pipe with a drop of 1 lb. and an initial pressure 

 of 120 lb. per sq. in., is 53.6 lb. per min. But as the drop 

 is 2 lb., the table value must be multiplied by ^2 and as the 

 length is 400 ft., it must also be multiplied by "V^. Hence, 

 the discharge for the given conditions will be 53.6 X "V2X \igg 

 = 37.9 lb. per min. 



Resistance of Elbows and Valves. The presence of elbows, 

 bends, and valves in a steam pipe increases the resistance to 

 the flow of steam and thus increases the drop of pressure 

 between the inlet and outlet ends. It has been found that the 

 resistance caused by an elbow or a sharp bend is approxi- 

 mately the same as the resistance of a length of pipe equal to 

 60 times the diameter, and that a stop-valve has a resistance 

 equal to that of a length of pipe of 40 diameters. In using 

 the foregoing formula for the weight of steam discharged, 

 therefore, the value of L should be the equivalent length of pipe, 

 taking into account the bends and valves. The method of 

 doing this is illustrated by the following example: 



EXAMPLE. What is the equivalent length of 300 ft. of 3-in. 

 pipe containing four elbows and six stop-valves? 



