WOOD PIPE FOR CONVEYING IRRIGATION WATER. 31 



circulation of air and the consequent drying of the wood during the 

 winter. 



In the operation of pipe lines, especially irrigation " siphons," 

 conditions frequently favor the admission of air, which may very 

 materially reduce the carrying capacity, and sometimes it is suf- 

 ficient to cause pulsations or vibrations so violent as to be a menace 

 to the life of the pipe. This difficulty is usually remedied by the 

 introduction of air vents at the top of the pipe near the intake, 

 carrying them back up along the pipe itself, or perhaps to one side 

 of the line to a point above the hydraulic gradient. 



The cost of maintenance in the operation of wood pipe lines varies 

 greatly. In many instances where there has been a careful selection 

 of materials, good construction, and favorable conditions of service, 

 the expense of maintenance may be for many years an almost neg- 

 ligible amount, while again, where the above conditions do not ob- 

 tain, the cost for repairs and upkeep may be considerable. It is 

 usually less during the first few years than it is later on in the life 

 of a pipe. 



A. P. Merrill, manager of the Utah Power Co., in connection with 

 his experience in operating a number of pipe lines aggregating 10 

 miles or so in length, writes as follows : 



The maintenance of pipe lines depends, of course, on the manner in which 

 they are constructed. At this time I have no definite maintenance costs which 

 can be given to support any statements that I might make. In general, how- 

 ever, I should say that a wood pipe line properly constructed with Kelsey joints 

 and laid under sufficient pressure requires practically no maintenance, at least 

 during the first 10 years. We have had comparatively new lines, however, 

 where the construction was somewhat faulty in some respects, and where the 

 butt joints were not used, which require more or less maintenance work during 

 each year. 



Eugene Carroll, manager of the Butte Water Co., in writing con- 

 cerning the pipes built at Butte in 1892, 1899, and 1900, makes the 

 following statement : x 



The pipe connects our reservoirs, one 13 miles and the other 22 miles out, 

 with our reservoirs in town. The watchman, which we have to keep at each 

 reservoir, makes a trip over the pipe line once a week. Occasionally in making 

 these trips it is necessary to dig out the pipe for small leaks, such as worm 

 holes on butt joints, but with two exceptions we have never had to use more 

 than two men in repairing leaks, and have never had to shut off the water. 

 Our two exceptions are, first, during the winter of 1S93 ice formed inside of 

 our pipe line, being caused from the fact that our reservoir was not completed, 

 and a jam was caused inside the pipe, bursting it, requiring the shutting off: of 

 the water and about 12 hours to repair it. Last spring on our new pipe line 

 a leak developed near one of our valve chambers, and before it was discovered 

 and the water shut off a bad washout took place, which washed the supports 

 away from the pipe line for about 1,000 feet, necessitating the rebuilding of the 

 line, taking about four days to do it. 



1 Trans. Amer. Soc. Civ. Engin., 58 (1907), p. 73. 



