Dosing accuracy is maintained, despite fluctuating system pressure

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Grundfos Alldos has enhanced the Flow Monitor for its diaphragm dosing pumps in the DIGITAL DOSING™ range. With the new AutoCal function, users now not only have problematic chemicals under control but also demanding processes. The new generation Flow Monitor makes the time-consuming manual pump recalibration procedure for fluctuating system pressures a thing of the past. Digital pumps equipped with this technology are calibrated at the factory and now compensate for all pressure fluctuations by automatically recalibrating themselves.

Rising and falling pressure and the constant need to manually recalibrate the dosing pump to ensure the flow rate can be maintained at a constant level and at the setpoint is a nightmare for all users who have to handle demanding processes and take into account fluctuating system pressures. With conventional diaphragm dosing pumps, every change in system pressure, and thus in the pressurised line, leads to a change in the pump’s stroke volume, with the effect that the medium is no longer added to the process in the correct quantity. This inevitably produces results that reduce quality and are not cost-effective. In conventional dosing pumps, this problem can only be avoided by constant recalibration or by adding costly flow measurement and control technology.

Fortunately, DIGITAL DOSING™ technology from Grundfos Alldos has long since made setting the dosing pump using the stroke length a thing of the past. Instead, using stepper and EC motors with a multi-sensor control circuit enables optimum control of suction and pressure strokes with a constant stroke length. The decisive advantage here is that suction is always performed with the full stroke volume. This ensures digital dosing runs particularly smoothly, with low pulsation and without any problems – a key factor when dosing difficult media.

But Grundfos Alldos can now do more than just offer the optimum solution for problematic dosing media. With the Flow Monitor specially enhanced for type DDI 222 digital dosing pumps and its AutoCal function, users finally also have system pressure fluctuations under control. The new AutoCal function therefore brings to an end time-consuming manual and repeated recalibration of pumps in response to fluctuating system pressures. Pumps equipped with this technology are calibrated only once at the factory for media with a viscosity similar to that of water. Provided the medium to be dosed has a comparable consistency, further calibration becomes completely unnecessary. One on-site recalibration is sufficient for pumping media of a different viscosity. Users can then sit back and relax as the DDI 222 itself now compensates for all pressure fluctuations by automatically and continuously adjusting to changing conditions.

The pump receives information on changing pressure conditions via a pressure sensor integrated into the dosing head, i.e. directly where dosing takes place. The integrated microprocessor also recognises at any point in time the exact position of the EC pump motor and thus also the diaphragm. These two pieces of information combined are sufficient, and the pump can immediately adapt its input speed automatically as required. Rising system pressure lowers the stroke volume, enabling the volumetric flow to be kept constant by increasing the stroke frequency. If the system pressure falls, the stroke volume rises and the stroke frequency is lowered in accordance with the pressure differential. This ensures the DDI 222 can always continue dosing exactly in accordance with the setpoint with consistently high precision.

This elegant and reliable solution from Grundfos Alldos is an instant hit with users when it comes to running costs. As well as the time saved on recalibration, the much improved process quality ensures fewer worries and more budgetary freedom. This solution delivers not a droplet too much or too little, even with difficult media and discontinuous processes.

Grundfos Alldos also demonstrated a keen awareness of the growing demands of cutting-edge dosing applications when launching the Flow Monitor. The method of flow control using intelligent pressure monitoring in the dosing head combined with a constant flow of information on the diaphragm position was unique and this continues to be the case today. Now with AutoCal comes system pressure compensation – another outstanding boost to reliability and dosing quality.

A further highlight of the DDI 222 is the full-PTFE multi-layer diaphragm supplied as standard. If there is a defect in the working diaphragm, the pump continues to dose with an equally robust second diaphragm without any interruption to the process. If a diaphragm sensor is integrated into the dosing head as an additional option, it immediately issues an error message in the event of leakage involving the first diaphragm. However, replacing the diaphragm can wait until a more suitable opportunity presents itself. A further bonus of the full-PTFE diaphragm over coated diaphragms is the increased service life and resistance to chemicals.

The DDI 222 with the new Flow Monitor is therefore the number one choice in dosing pumps for managing the most common faults in difficult processes:
  • Fluctuating system pressure
  • Leakage in the suction and pressure valves
  • Air and gas bubbles in the dosing head
  • Cavitation
  • Inadmissibly high operating pressure
Thanks to its optimum reliability, the DDI 222 thus meets the needs of users like no other dosing pump on the market in the following areas:
  • Dosing antiscalants and antifouling agents in diaphragm filtration and reverse osmosis
  • Dosing a wide variety of chemicals in areas such as paper production
  • Dosing cleaning agents and disinfectants
  • CIP applications for the food and beverages industry
  • Dosing highly concentrated acids and lyes in treatment and neutralisation processes for industrial and process water
  • Dosing viscous media
  • etc.

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