46 



3rd. They do not interfere with traffic and cultivation. 



4th. They do not collect the seeds of weeds and distribute them on the* 

 irrigated land. 



5th. They minimize the cost of maintenance. 



Where cement pipes have been found deficient it has almost always been 

 due to defects in the process of manufacturing. The use of cement pipes, 

 during the last few years has been extended to other states and there are 

 now many miles of pipe on some of the irrigation systems of eastern. 

 Oregon, eastern Washington, and Idaho. During the past two years several 

 miles of pipes have been manufactured by the Pruitlands Irrigation and 

 Power Company, near Kamloops, for use on the distribution lines of the 

 system. 



The cement pipe so extensively used in southern California is made in: 

 sections two feet long. One end of the pipe tapers in and the other end 

 tapers out so that when two pipes are joined together they form a bevelled 

 lap joint. This form of joint is preferred to bell joint used for sewer pipes 

 because the outside of the pipe is straight and the pipe is easier to lay; it 

 also requires less material to manufacture. The pipe is made by means of 

 metal moulds in which a moist mixture of cement and sand or cement and 

 gravel is very carefully tamped. The mixture is comparatively dry in order 

 that the moulds may be removed to be used again immediately after the- 

 tamping is finished. This is necessary to obtain a large output with one set 

 of moulds and as much as 100 feet a day of 30 inch pipe and 500 to 400 

 feet of 6 to 8 inch pipe are made by experienced pipe men with one set. 

 After the pipe is made it is carefully cured by being kept moist for at least 

 one week and allowed to harden. At the end of a month it is ready to be- 

 laid and joined in the trench with cement mortar. 



The sizes -commonly used are 6, 8 and 10 inches inside diameter for 

 private distributing line and 10 to 30 or even 36 and 48 inches for the- 

 main lines of the irrigation system. The sizes to use in any case depend 

 on the desired carrying capacity and the grade or fall obtainable. 



The cement pipe, as manufactured by this dry process, has not the same 

 strength nor is it as impermeable as a pipe made with a wet concrete and 

 can only be used to cross shallow depressions or where the pressure is 

 very moderate. The pressure head which it will safely stand depends on 

 the efficiency of the manufacturer, the mixture used and the diameter of" 

 the pipe. The writer recommends the following maximum values as safe 

 for pipes manufactured with care: 



By using unusual care, experienced pipe men can make pipe which will 

 stand safely 30 per cent, greater heads than those given in the above table. 



The use of hand tamped non-reinforced pipe is therefore limited to low 

 pressures and great care must be used in planning and constructing pipe 



