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Instrumentation and control systems for reliable, monitored operation.
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The ModFlow System is a control system developed by AQUAZUR® using a programmable logic controller. The PLC actuates a control valve mounted on the filter water discharge pipe, creating a secondary head loss that compensates for filter fouling.
Ultrasonic level → ModFlow controller → modulating outlet valve, with position feedback closing the loop.
ModFlow uses a slow, incremental, timed adjustment strategy rather than classic PID control. At each cycle the valve is moved by a single small step — and only after a set interval — so the process is never hit with rapid swings that would upset filtration.
PID loops tend to struggle in water treatment because of long process dead times, non-linear valve characteristics, variable process gain, slow actuators and sensor noise — conditions that easily push a tightly-tuned controller into hunting and instability.
The incremental method instead mirrors the way a plant operator trims a valve by hand — nudge, wait, observe — which keeps the controller predictable, forgiving, and easy for operators to trust.
In automatic mode the controller steps the filter through a clear sequence of states, each with its own operator status message:
Valve closed at 0%. The block sits idle, waiting for a filtration-start command.
Valve held at the start position while the filter level rises up into the deadband.
Once the water level reaches the min setpoint level, the outlet valve ramps to a preset position and waits for position feedback to confirm it has arrived. Then the valve will start modulating.
Normal running. Each cycle the valve is nudged one small step open or closed to hold the level inside the deadband.
On a clogged-filter detection or a fault, the valve is driven back to 0% and filtration stops.
The ModFlow controller regulates valve movements according to the signals delivered by the ultrasonic level sensor situated inside the filter bed, measuring the water height and valve positioner so that:
Under stabilised operating conditions, the level of water in the filter remains close to its set point, irrespective of the flow rate.
During restarts after a wash, or in the event of a change to the flow rate, the filter gradually comes up to speed, without any surges, in order to minimise outlet turbidity peaks.
Each filter is equipped with a ModFlow Controller. The battery of filters are usually connected through a network (Profinet). Each system is controlled individually by each controller, but the battery can be viewed remotely.
Equipment specific to each filter (valves, sensors …) is connected to the relevant ModFlow Controller that transmits data delivered by the sensors to which it is connected. Valves and sensors on washing equipment and on auxiliary equipment common to the filter battery are connected to the main programmable logic controller.
The main programmable logic controller is responsible for managing the operation and the washing of the entire filter battery. It actuates the control mechanism and the valves for each filter by transmitting its signals via the ModFlow Controller, which in turn controls the controller valve setting.
The ModFlow Controller combines all the principles that are characteristic of good filter control:
Stable instantaneous output and slow flow-rate fluctuations whenever plant operating conditions change, giving consistent filtered-water quality.
Constant-level, upstream control. Stable water depth over the bed avoids the danger of occasional vacuums forming within the filter bed.
Reliability through a few simple, robust sensors and networked, proven-technology programmable logic controllers.
Optimised battery management, incorporating backwash management and control across the whole filter battery.