MIL-HDBK-1164
(2)
Repeat the process of starting and stopping the pump at 3-
to 5-minute intervals until the discharge runs clear. Water running back down the
pump column just after the pump is stopped may cause the motor and impeller to turn
in a reverse direction. Do not attempt to start pump during this reverse rotation.
h)
Backwashing and Surging. When surging alone is not sufficient,
backwashing may be used. This procedure consists of allowing a large volume of
water to rush down the casing. Follow these steps:
(1)
Where bypass pump connections or wash-water lines are
not included in the installation, remove the flap in the check valve.
(2)
Open the pump discharge valve and allow a full head of
water from the storage tank to rush down the well casing. If the casing fills rapidly, it is
because the screen is badly clogged.
Caution: Before starting the backwash operation, be sure the pump and
motor turn freely. Otherwise, the downrush of water may rotate the pump in the wrong
direction and unscrew the pump shaft.
(3)
Allow the backwashing to continue for approximately 5
minutes. Then close the backwash valve, open the pump discharge valve, and start the
pump. Run the discharge to waste until the water is clear. Repeat the operation.
Check the results by measuring the water level and yield.
i)
Backwashing and Backblowing. A combination of backwashing
with water and backblowing with air may be used, if the well pump has been pulled.
The compressed air increases the surging action and provides air-lift pumping that
removes dislodged sand. Use experienced personnel for this operation, and follow this
procedure:
(1)
Remove the well pump and insert a 4-inch eductor pipe to a
depth according to Table 4. The arrangement of eductor pipe and air line is shown in
Figure 4.
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