30 
BULLETIN 462, U. S. DEPARTMENT OF AGRICULTURE. 
The size of main needed depends on the number of laterals it is 
required to operate at once, or, in other words, the acreage that is to 
be watered at one time. 
Table 2 gives sizes of mains needed for different quantities of 
water, according to the acreage to be watered. The data in this table 
are of a general nature and may be modified to suit the specific condi- 
tions. By following the sizes of the pipe as indicated below there 
will be ample capacity for the successful operation of the system 
under all conditions encountered. 
Table 2. — Size of pipe for main supply line. 
Discharge in gallons per 
Length of line in feet. 
minute. 
50 
100 
200 
300 
400 
500 
600 
700 
30 
Inches. 
? 
31 
4 
4 
Inches. 
2 
2| 
2\ 
3 
3^ 
3j 
4 
5 
Inches. 
2 
21 
3 
3 
31 
4 
4 
5 
Inches. 
2 
3 
3J 
4 
4 
5 
5 
Inches. 
2-1 
3 
3 
31 
4 
4 
5 
6 
Inches. 
21 
3 
31 
31 
4 
4 
5 
6 
Inches. 
21 
3 
31 
4 
4 
5 
5 
6 
Inches. 
21 
3 
100 
31 
4 
150 
200 . 
4 
300 
400 
6 
500 
6 
The above system is in operation on about 150 acres within a few 
miles of Williston, in the north-central part of the State. The plants 
are mostly small, usually irrigating not more than 10 acres, one plant 
which irrigates 55 acres being an exception. The water supply for 
this plant is obtained from a bored well about 100 feet in depth, and 
is pumped from the well into the main by a steam duplex pump with 
rated capacity of 700 gallons per minute, operated by a 70-horsepower 
steam engine. The plant is designed to irrigate about 20 acres at 
one time, which requires a 7-inch main at the start. This is reduced 
to a 5-inch main at the end of the field, and might be reduced still 
more but for the fact that this pipe supplies water also to about 60 
acres of surface-irrigated land. Much of the pipe is second-hand, and 
there is no record of its cost, but it is estimated that to replace it 
with new galvanized pipe would cost about $100 per acre for the field 
laterals and an additional $150 per acre for the pump, engine, and the 
main. This would mean a total cost of $250 per acre, or approxi- 
mately $13,750 for the system, complete. The owner burns wood, 
which is plentiful in this section. He estimates that with wood 
he can operate his plant for 24 hours, the wood costing only $1.25 
per cord. This is exceedingly low for operating expenses. The 
plant is run day and night continuously when it is in operation 
at all, owing to the difficulty of getting up steam every day ; also be- 
cause irrigation at night is found to have a number of advantages, 
such as smaller loss by evaporation and prevention of scald. 
