138 Bulletin 86 



three quarts at a time, were still coming out of the pipe line at inter- 

 vals of about a minute, and this was an hour and forty minutes after 

 the gates had been adjusted. On the east side of the railroad this 

 effect was not encountered. On that side the line has an ascend- 

 ing grade and the entering water doubtless carries all the air out 

 promptly. 



The important bearing of these observations is that, as in many 

 other lines of design, a factor of safety is necessary in designing 

 pipe lines on descending grades, and, furthermore, there should be 

 many air vents or open standpipes on descending grades. In com- 

 puting capacities, pipe lines are assumed to be running full of water, 

 but no recognition is made of possible unfavorable conditions. It 

 is interesting to note from Table XIX that the friction loss between 

 Lateral No. 3 and the railroad was 43 percent greater in one test 

 made 18 minutes after adjusting the gates than in another test made 

 3 hours and 20 minutes after adjusting the gates. Also, in the 

 same line, on October 8, with a discharge of 2.08 second-feet, the 

 loss of head decreased from 8.65 feet Z7 minutes after adjusting the 

 gates for this test to 8.22 feet one hour after adjusting the gates, 

 and 8.00 feet 1 hour and 24 minutes after adjusting the gates. 



From all the above tests it may be concluded that the friction 

 factor, "n," for hand-tamped and washed pipe is .013 and for ma- 

 chine-made pipe the factor is a little less than .013. This assumes 

 that the joints are well made by careful workmen. If it is assumed 

 that the joints will be left rough and projecting on the inside, then 

 the designers should use a friction factor of .014 or .015. 



CAPACITY TABLES 



As a basis for determining the proper sizes of pipe required in the 

 design of any particular project. Table XX has been prepared. This 

 table is computed from Kutter's formula, using a friction factor of 

 .013. This is a conservative basis for straight lines without risers, 

 and well executed machine-made cement pipe lines may have some- 

 what greater capacities than those given. 



In the case of lines with tee risers of the same size it will be 

 about right to assume an increase of friction loss of 12^ per cent 

 for each riser in 100 feet of pipe*. Thus, if the risers are spaced 50 

 feet apart, increase the allowance for friction 25 per cent ; if they 

 are spaced Z2i feet apart, increase the allowance about 38 per cent. 

 Sometimes tee risers of smaller size than the pipe line are used. In 



*See page 136. 



