Pneumatic Control System

The pneumatic control system (also called a bubbler tube control system) is a relatively simple system that can be used to control one or more pumps. The system consists of an air compressor; a tube extending into the well, clear well, or storage tank/basin; and pressure-sensitive switches with varying on/off set points and a pressure relief valve (see Figure 10.10). The system works on the basic principle of measuring the depth of the water in the well or tank by determining the air pressure

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Compressor i-y>

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Pump Pump Pump

Figure 10.10 Pneumatic system for pump motor control.

necessary to just release a bubble from the bottom of the tube (see Figure 10.10)—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 air line 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 additional 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 set to activate at a third preset well or tank depth (e.g., 4.6 ft or 1.99 psi) and to cut off a preset depth (e.g., 3.0 ft or 1.3 psi).

The pneumatic control system is relatively simple and has minimal operation and maintenance requirements. The major operational problem 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.

To pump controls

Figure 10.11 Electrode system for pump motor control.
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