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'Deragging' software now available on the Danfoss VLT AQUA drive

29 September 2011

Waste water from households and industry contains particles and fibres that are not removed by screen filters. These fibres (particles) will build up on the impeller vanes of wastewater pumps, leading to poor efficiency and extensive pump wear. The maintenance of these pumps can be expensive and time consuming, often requiring special lifting equipment. So-called ‘ragging’ is a serious ongoing issue.

Now, thanks to new technology from Danfoss, ‘Deragging’ software is featured as standard on the VLT AQUA drive, which ensures that highest pump efficiency is maintained and impeller wear is minimised, while allowing for programmable ramps and time delays. This feature optimises the efficiency of the pump by constantly monitoring the motor shaft power consumption relative to flow and reacts with a reverse spinning cleaning cycle when a deviation from the power consumption of the system design is recorded.

Proactive cleaning:  This intelligent system is fully flexible and can be optimised to meet the individual needs of applications. Using the Danfoss ‘Deragging’ feature you can perform proactive cleaning. During the simple commissioning sequence, the user can determine when the system should react – at start command, stop command, timer based via a digital input (every morning at 8.00 for example), via serial communications or using a number of logic rules that can be programmed. All parameters are grouped together so programming is easy.

Reactive cleaning:  During operation, a power monitoring system will ensure that a cleaning cycle starts when the pump takes more energy from the drive than it normally should. In this situation the pump is already starting to clog. We should prevent clogging by adopting proactive cleaning. In the Danfoss VLT® AQUA Drive, reactive and proactive cleaning can be combined.

Danfoss recommends that proactive cleaning is programmed by the user and that automatic reactive cleaning takes place as and when necessary between the proactive cleaning cycles.

Cleaning pattern
The impeller is cleaned by running the pump quickly in the opposite direction. The user can define how many times the drive should spin the impeller in reverse, at what speed and for how long. However, users should be aware that not every pump can be run in reverse and that checks with the pump manufacturer must be made before specifying this type of control.

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