Digital DosingTM Unique Solutions for Challenging Dosing Processes - Matthias Ulmer

Disinfection, neutralisation, precipitation and flocculation are essential physical and chemical processes of water treatment and wastewater recycling. Modern, highly efficient chemicals have to be used economically and with minimal impact on the environment. Some of these chemicals are very difficult to handle, and this overstrains conventional dosing pumps. These challenges can be met by digital dosing pumps with modern drive technology and control software.

The chemistry in water treatment, water and wastewater recycling has experienced a huge development during the last 15 years, and this poses a challenge for today’s dosing technology.

Additionally, more and more complex applications require intelligent dosing pumps with new drives or new control and adjustment mechanisms to simplify the operators’ job. This in turn ensures reliable, cost-effective, and high-precision processes.

Grundfos Alldos have accepted and met these challenges with their digital dosing pumps. These offer state-of-the-art drive technology and new dimensions of user-comfort, energy efficiency and dosing characteristics.

Higher requirements in control tasks and process reliability
With conventional dosing pumps, the dosing quantity can be adjusted by changing some parameters such as stroke length and frequency. These factors have to be combined in the right way in order to get the right dosing performance. Furthermore, the adjustment range is usually limited. As a consequence, the correct pump type has to be selected for each single application. Increased control requirements, such as dosing in proportion to the volume via 0/4-20 mA or dosing control feedback to a central control system, can only be realised with supplementary installations and accessories.

The new digital dosing pumps put an end to complex adjustments via stroke length and frequency. Stepper motors and EC drives with multi-sensor control circuits optimally fulfil the requirements due to variable, adjustable suction and dosing stroke speed. This unique feature ensures an optimal dosing characteristic and high precision even at a turndown ratio up to 1:1000, e.g. the DME 940-4 easily achieves a flow range from 1.2 to 940 l/h.

Further integrated standard features of digital dosing are: direct adjustment of the required capacity in ml/h, l/h, or gph, volume-proportional dosing via ml/pulse or 0/4-20 mA scalable analogue control, and time- or pulse-controlled batch dosing.

Thanks to the wide flow range and flexible control options one single pump type can be used flexibly within one application. This keeps investment and maintenance costs at a low level.

The FlowMonitor and the Dosing Monitor detect – without any mechanically actuated parts – problems such as air-bubbles or system overpressure, and automatically display an error message. The latest development in this area is the AutoCal function, also based on pressure sensor technology. Now, even system pressure fluctuations have no influence on the dosing accuracy, as the motor speed is adjusted accordingly. This cost-effective solution increases the process reliability.

Precise dosing of highly concentrated chemicals to reduce both costs and environmental impact.

The higher the concentration of the chemical, the more important is the dosing precision in order to reduce costs and environmental impact. Conventional dosing pumps fail through lacking precision. This can lead to over- or underdosing and to suction problems when dosing minimum volumes.

The very high precision is a result of a combination of factors: digital input of the dosing capacity without stroke adjustment, a calibration function to adjust the pump according to the properties of the dosing liquid, a positive crank drive of the diaphragm as well as an optimised dosing head and valve geometry. These are the key factors for environmentally friendly and cost-efficient dosing of chemicals.