USE OF CONCRETE PIPE IN IRRIGATION. 



9 



under heavy pressure. In other respects the pipe is made as de- 

 scribed under hand-tamped methods. 



Troweling machines make use of iron vanes that force the con- 

 crete down and against the outside form. The vane or packerheacl 

 apparatus is revolved by machinery and at the same time is lifted 

 from bottom to top of a length of pipe while it is being made. There 

 are a number of different types of this class of machine, many of 

 which make pipe very rapidly. The troweling process usually makes 

 a pipe of smooth interior finish. 



Fig. 3. — Concrete-pipe yard showing forms and cast-iron rings. 



It is probable that other types of concrete pipe machines will 

 come into the market in the near future. A machine that both tamps 

 and trowels pipe is used now. Another machine has been recently 

 invented that compresses the concrete in the molds by squeezing in 

 the outside form. Many other possibilities are talked of which may 

 soon become realities. 



QUALITY OF CONCRETE PIPE. 



Both hand-tamped and machine-made concrete pipes are often of 

 very inferior quality, but it is encouraging to know that the quality is 

 constantly improving. Most pipe makers will agree to deliver a 

 high-grade pipe if the purchaser is willing to pay for it, but as long 

 as the latter insists on getting the cheapest pipe he is apt to get the 

 poorest quality. Some reputable firms, however, will not make an 

 inferior grade and do not try to compete with pipe makers who sell 

 3445°— 21 3 



