When the pump fails to build up pressure and the
greater weight or is exerting a greater static pressure
discharge valve is open and the pump speed is
than the column containing air. Thus the air-water
increased, the procedure to use consists of four steps as
column is forced upward until it discharges over the
top of the U-shaped pipe.
Secure the pump.
Prime the pump and ensure that all the air is
expelled through the air cocks on the pump
3. Open all valves on the pump suction line.
4. Start the pump again. If the pump is electric-
driven, be sure the pump is rotating in the correct
direction. If the discharge pressure is not normal when
the pump is up to its proper speed, the suction line may
be clogged or an impeller broken. It is also possible that
air is being drawn into the suction line or into the casing.
If any of these conditions exist, stop the pump, try to
find the source of the trouble, and correct it, if possible.
Air-lift pumps are used entirely in well pumping.
Unlike the pumps studied earlier, the air-lift pump
needs no moving or rotating mechanism to produce
liquid movement. Instead, the pump uses compressed
air to move or lift the liquid.
The air-lift pump operates on the principle that
water mixed with air has less weight, or is more
buoyant, than water without air. When compressed air
is introduced, a mixture of water and air is formed in
one leg of the U-shaped pipe, as shown in figure 6-25.
The solid column of water in the other leg now has
In practice, of course, wells are not dug in a U-
shape. Figure 6-26 shows a CENTRAL AIR-LIFT
PUMP. Compressed air is led down an air pipe to a
nozzle or foot piece submerged well below the water
Figure 6-25.Principles of an air-lift pump.
Figure 6-26.Central air-lift pump.