19 BULLETIN 495, U. S. DEPARTMENT OF AGRICULTURE. 

Fic. 6.—Deep-well pump in casing to per- 
mit installation of pump below ground- 
water level. 
~a pressure tank, where the veloc- 

bearing stratum is intercepted. 
Care should be exercised to case 
off strata having a weak flow if 
strata having stronger flow are 
encountered in the same well,. 
because water may be forced out 
of the well into the weak strata 
so that they will be a source of 
loss rather than gain. Each 
water-bearing stratum should be 
tested before the final casing is 
sunk, so that the well screens can 
be properly located and propor- 
tioned in size and mesh. : 
SCREENING WATER. | | 
A difficult factor to control in 
many water supplies for spray 
irrigation is the clogging of noz- 
zles and pipe lines by sediment, 
moss, lime, or other matter. This 
is true especially with the over- 
head system, where many small 
nozzles must be kept clean. The 
most desirable place to remove 
clogging matter is before the 
water enters the suction pipe of 
the pumping plant. Screens of 
different forms are placed inthe 
“turning unions” at the feed 
end of each lateral, but these 
screens can remove only a small 
amount of material before they _ 
in turn must be cleaned. Sands 4 
from wells or other sources may 
be collected to a certain extent 
by placing in the main pipe line 
an enlarged chamber similar to 














ity is checked and the sand © 
grains settle out. Underextreme ~ 
conditions it may be necessary to 
reservoir well waters and re-— 
pump after settling. Bucket- 
type screens for installation in 
