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 packerhead 
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. 
f mm 
&JL 
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 2 
