MIL-HDBK-1164
Caution: When starting backblowing operations, do not start at maximum
rates. Keep the gravel chamber full at all times to replace sand loss.
(8)
For this operation, provide excess air. The desirable
amounts of excess air, with 50 percent submergence, are shown in Table 5.
Table 5
Air Requirements for Backwashing Well Screen with Air-Lift
Lift
Air Required
feet
(m)
cfm/gallon pumped
(Lps)
100
(30)
0.5
(0.2)
200
(60)
0.7
(0.3)
400
(120)
1.0
(0.5)
500
(150)
1.5
(0.7)
4.5.3.2 Repairing Well Screens. It is sometimes desirable to pull a heavily encrusted
screen for cleaning. Likewise, a screen suspected of being damaged by corrosion can
be pulled and inspected. On screens that have been pulled for any reason, check the
wire windings, bail plug, and packer. If the screen has corroded away or been
damaged, replace it with a new screen or return it to the factory for repair. Generally,
field repair of well screens is neither practical nor effective.
4.5.3.3
Maintaining Specific Well Types. In addition to the general maintenance
items common to all wells, different types of wells require special care because of their
particular construction or operation. Groundwater supply maintenance procedures are
summarized in Table 6.
a)
Bored Wells. Casing failures and screen clogging are the primary
causes of failure in bored wells. High turbidity in the water may indicate that the screen
needs cleaning or replacement.
b)
Dug Wells. The masonry or concrete casings are subject to cracks
and joint failure that can allow surface water into the well. Well bottoms can fill with silt
and sand, which will require periodic removal.
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