FSA100 Rev1206
20
THEORY OF OPERATION
The operation of the AutoFoam system is controlled by a microprocessor housed
in the control module. The programming enables the AutoFoam system to operate in
three different modes.
Automatic Mode
This is the normal mode of operation. In this mode of operation the flow rate of
foam concentrate is determined by the percent selected on the control module and
inputs from the flow sensors. The microprocessor controls the opening or closing of
the metering valve to provide the correct foam solution at the pump discharge.
When in the automatic mode the flow sensors provide constant feedback of flow
rate information. Dual flow sensors mounted on the metering valve assembly monitor
foam concentrate flow rate. The discharge flow sensor measures the solution (foam
concentrate and water mixture) flow rate at the discharge side of the pump. This flow
rate information allows the system to maintain the selected foam proportioning regardless
of discharge fluctuations.
The metering valve controls the amount of foam concentrate that flows into the
eductor. The eductor injects the foam concentrate into the suction side of the pump.
The flow rates of the foam concentrate and the foam solution is processed. The flow
rates are displayed and the metering valve is adjusted to produce the selected foam
proportion.
If input data from one of the dual foam concentrate flow sensors is lost the program
will automatically use the information from the one that is operating properly. There is
no loss in performance or accuracy of the system. If input data from both foam flow
sensors is lost, the AutoFoam system will switch over to the fixed program mode.
Fixed Program Mode
The system will enter this mode when there is no input data from both foam
concentrate flow sensors. In this mode of operation the flow rate of foam concentrate
is determined by information stored in the AutoFoam program. When the system is in
this mode an F will be shown in the upper display. The AutoFoam system will exit the
fixed program mode automatically when input data from a foam concentrate flow
sensor is detected.
The foam concentrate flow rate is determined by the percent selected on the control
module and water flow at the discharge. It is an important factor in determining if there
is a failure in the AutoFoam system when there is no input data from the foam concentrate
flow sensors.
When in the fixed program mode stored precalibrated valve position data is used
to adjust the metering valve. There is a transducer in the valve assembly that provides
feedback on the valve position. The valve position is directly related to how much
foam concentrate flows. The program uses the selected foam proportion percent and
the discharge water flow rate to position the valve for the correct foam concentrate rate
of flow.
