SCIENCE OF THRESHING. 4! 



through the straw pipe exceeds that of the straw, 

 that is, there are more pounds of air than pounds of 

 straw set in motion by the fan. So, in determining 

 the work performed by the fan, the item of air can 

 be figured, as the more straw there is, the less air 

 there is, and consequently the less weight. The 

 actual foot pounds or horse power expended is 

 determined as follows: Multiply the area of the 

 straw pipe by the number of feet the air travels per 

 minute; multiply this by the pressure required to 

 produce this speed; the result, which gives the 

 number of foot pounds, divided by 33,000 is the 

 horse power. Thus, the area of the usual 15 in. 

 stacker pipe is 176 sq. in. A pressure of one ounce 

 per sq. in. gives a velocity of 5.161 feet per second to 

 the air.- 176X5.161=908,336 ounces, which, di- 

 vided by 1 6, the number of ounces in a pound, equals 

 56,271 foot pounds. Dividing this by 33,000, the 

 number of foot pounds in a horse power, equals I J4 

 horse power approximately. At this velocity and 

 pressure about 14 tons of air and straw per hour 

 pass through a 15 inch pipe (of which about ten 

 tons of air and four tons of straw represent a fair 

 average.) There is of course more dry straw blown 

 through in a given time than wet straw. 



Some power is lost by leakage around the fan and 

 at its center; also cutting and chopping the straw. 

 A slow moving fan moving a large amount of air 

 steadily is better . than a fast turning one, as the 

 increased friction of the more rapid current absorbs 

 a great deal of energy. Some experiments along this 



