8 BULLETIX 906, U. S. DEPARTMENT OF AGRICULTURE. 
The cost of laying is estimated at about 1 cent per foot for each 
inch of diameter of pipe, but conditions may arise where it may be 
much more, especially if siphons are installed. 
MANUFACTURE OF PLAIN CONCRETE PIPE. 
Plain concrete pipe may be divided into two general classes — 
hand-tamped and machine-made pipe. Hand-tamped pipe is made by 
tamping concrete between inside and outside collapsible forms. The 
forms usually run from 6 inches to 36 inches inside diameter. The 
pipe is made for the most part in 2-foot lengths, although some is 
made 30 inches in length. In making hand-tamped pipe, the forms 
are set up vertically on the ground or on a platform. Concrete is 
then poured between the forms by one man while another tamps. 
When the pipe is finished it is reamed off on top with a special 
reamer. The inside form is first removed by collapsing it and the 
pipe carried to the proper place in the yard, where the outside form 
is removed and the pipe allowed to set. Pipe should always be 
kept thoroughly moist for at least 10 days before it is cured. If 
the concrete is moist enough when the pipe is tamped the outside 
form may be stripped, i. e., pulled off vertically, without loosening 
the jacket. If so-called dry pipe is made, the forms can not be 
stripped, but the outside form must be loosened before lifting it off. 
The tongue and groove ends of the pipe are made to assist in lay- 
ing. The groove end, which is usually a simple inside taper on the 
bottom of the pipe, is made by dropping a cast-iron ring between 
the forms. This ring is beveled to conform to the groove of the 
pipe, and is allowed to remain on the bottom of the pipe until the 
concrete has set sufficiently to move the pipe. (Fig. 3.) The tongue 
end of the pipe is made when the pipe is finished, and is accom- 
plished by whirling the reamer over the top before the forms are 
removed. Some hand-tamped pipe is made with bell and spigot 
ends similar to the ordinary clay sewer pipe. When pipe is made in 
this way, the outside form is split so that the forms can be removed 
laterally. 
Pipe machines 2 are roughly classified as tamping machines and 
troweling machines. Some tamping machines tamp the pipe very 
similarly to the hand-tamping process. The mechanism of most of 
these machines causes the pipe to revolve under the tamper while 
the concrete is poured in between the forms. A pneumatic air tamper 
may be used to tamp the pipe. The apparatus operating the air 
tamper is suspended over the forms, the air tamper being guided 
around the shell of the pipe by one man, while another feeds the 
concrete. The pneumatic hammer delivers about 700 blows a minute 
2 Arizona State Experiment Station Bulletin No. S6, by G. E. r. Smith. 
