USE OF CONCRETE PIPE IN IRRIGATION". 13 
pressure pipe. Pipes of 8 to 12 inches in diameter are made in stock 
of double thickness, which will stand heads of 150 feet and over, but 
the prices are about three times as high as stock pipe. Stock pipe 
should be safe under pressures of from 20 to 35 feet. 
In connection with the above-quoted prices, it may be stated that 
many pipe manufacturers who operate small plants sell pipe much 
cheaper than the figures given. 
LAYING CONCRETE PIPE. 
Concrete pipe should be laid deep enough in the trench so as to 
reduce the range of temperature and to be safe from injury against 
plows, subsoilers or other farm implements. There should be at least 
12 inches of earth over the top of all kinds of pipe, and high 
pressure pipe should have a top covering of at least 18 inches. Tem- 
perature changes in the shell of the pipe are greatly reduced when the 
pipe is buried deeply, and less trouble is experienced from expansion 
and contraction. The moisture content within the shell of the pipe 
is likewise kept more uniform than where the upper half is laid near 
the surface of the ground. 
The trench should be wide enough to allow room for a man's feet 
when he is straddling the pipe in the act of laying the pipe. It 
is a mistake to make the trench too narrow, especially when large- 
sized pipe is laid, as there must be room to finish off the joints. 
Excavation in soil that is not too hard or rocky may be done with a 
plow and V scraper. Koad scrapers and ditchers are sometimes used 
to start large excavations, but trenches so made are too wide as a rule. 
There are several makes of tile trenching machines that are used for 
large installations, and where there are no obstructions to interfere 
with the machine it may pay to use one. These may be operated over 
the same trench twice, thus making it of nearly double width. For 
the most part trenching is done with pick and shovel — handwork 
being necessary where pipe is laid among full-grown trees in an 
orchard. 
Some contractors lay pipe by force account, charging a commission 
of 10 to 15 per cent for tools and supervision, for the reason that it 
is difficult to make an estimate of the cost of excavation, as trenching 
in hardpan, adobe, or soil full of boulders may cost several times as 
much as a trench in loose loam or sand. Some trenching in favorable 
soil has been done for 3 to 7 cents per foot for 12-inch pipe, while 
the actual cost of a trench for 24-inch pipe near Azusa, Calif., where 
bowlders were encountered, was about 35 cents per foot. Trenching 
for 12-inch pipe in adobe soil near Santa Ana, Calif., with a trench- 
ing machine w T as done for 5 cents per foot. Handwork for heavy soil 
often costs 15 to 20 cents per foot for 12-inch pipe. 
