Environmental Engineering Reference
In-Depth Information
Vent
Pump
1
Pump
2
Pump
3
Compressor
figure 3.10 Pneumatic system for pump motor control.
air pressure necessary to just release a bubble from the bottom of the
tube (see Figure 3.10)—hence, the name
bubbler tube
. The air pressure
required to force a bubble out of the tube is determined by the liquid
pressure, which is directly related to the depth of the liquid (1 psi = 2.31
ft). By installing a pressure switch on the airline to activate the pump
starter at a given pressure, the level of the water can be controlled by
activating one or more pumps.
Installation of additional pressure switches with slightly different
pressure settings allows several pumps to be activated in sequence. As
an example, the first pressure switch can be adjusted to activate a pump
when the level in the well or tank is 3.8 ft (1.6 psi) and shut off at 1.7 ft
(0.74 psi). If the flow into the pump well or tank varies greatly, and addi-
tional pumps are available to ensure that the level in the well or tank
does not exceed the design capacity, additional pressure switches may
be installed. These additional pressure switches are set to activate a
second pump when the level in the well or tank reaches a preset level
(e.g., 4.5 ft/1.95 psi) and cut off when the well or tank level is reduced to
a preset level (e.g., 2.7 ft/1.2 psi).
If the capacity of the first pump is less than the rate of flow into the
well or tank, the level of the well or tank continues to rise. When the
preset level (e.g., 4 ft) is reached, the second pump will be activated. If
necessary, a third pump can be added to the system that will activate at
a third preset well or tank depth (e.g., 4.6 ft/1.99 psi) and cut off a preset
depth (e.g., 3.0 ft/1.3 psi).
The pneumatic control system is relatively simple and has minimal
operation and maintenance requirements. The major operational prob-
lem involved with this control system is clogging of the bubbler tube. If,
for some reason, the tube becomes clogged, the pressure on the system
can increase and may activate all pumps to run even when the well or
tank is low. This can result in excessive power consumption, which, in
turn, may damage the pumps.
