Beating ragging – without hassle

Clearing out blocked pumps can be a costly and time-consuming business. But an innovative, hi-tech solution is proving to be a great success.

An automated solution is addressing the long-running and costly problem of ragging in sewage pumping stations and wastewater treatment plants across the UK.

Intelligent Pump Control (IPC), developed by variable-speed drives manufacturer Control Techniques, features a powerful Exor UniOP HMI touchscreen control panel supplied by sole UK distributor Scattergood & Johnson.

Ragging, the fouling of pump impellers, accounts for thousands of hours of maintenance time.

As well as being a dirty and unpleasant task, the process of clearing a blocked pump can easily cost hundreds of pounds – and can be required on a frequent basis.

Downtime may last several days, putting back-up systems under additional pressure and running the risk of total system failure. This can result in effluent leakage with implications for the environment, human health, clean-up costs and breaches of legislation.

However, the innovative high-tech solution, first applied successfully by Northumbrian Water at Seaton Sluice, is now proving its worth with other water companies.

It tackles the problem automatically – without the need for human intervention.


The system’s key feature is the detection of ragging at a very early stage, before it becomes a problem.

Control Techniques’ Unidrive IPC software is loaded into a PLC on-board module within the Unidrive SP (or Affinity) AC drive, which is capable of monitoring true load torque in real time.

The torque is user-definable via the UniOP HMI panel to accommodate specific pump characteristics.

Changes as small as 1-2%, indicative of potential ragging, are detected and, because the PLC is mounted within the drive, the application has a reaction time measured in microseconds.

Different pump operating routines are automatically applied to free the impeller as soon as any load change is detected within the pump system, preventing potential blockages.

Procedures to clear the impeller are multi-programmable and are tailored to suit client specification and individual pumping station operation requirements.

If these procedures fail to clear the problem, an alarm is triggered. An engineer can then remotely access the drive via the UniOP Ethernet connection, using Control Techniques software tools to assess the situation and perform manual operations.

The UniOP TFT panel, which includes Ethernet and USB connections, provides the ideal interface to the drive, providing monitoring, simple adjustments to drive parameters and remote access for data collection and diagnostics.

The UniOP, working together with the Control Techniques drive and IPC software, avoids the need for more traditional technology requiring expensive programming.

“We particularly like the UniOP HMI,” comments Control Techniques’ UK general manager, Dave Baston. “It has proved to be the ideal interface with IPC systems. The UniOP HMI range gives us ease of communications, has all of the macros to allow us to link to the drive structure and very user-friendly programming.

“With the new wide-screen models we have been able to incorporate graphics for four pumps for instance – which makes it easier for customers – and the graphics are very clear and easy to read. The user can access diagnostic data on individual pumps; how efficient they are, how many cleanses have been carried out and much more.

“We are now encouraging users to fit flow meters so that this information can be incorporated into the display too. There’s plenty of scope for future development.”

The IPC software takes into account static and dynamic heads in the pump installation and factors in pump characteristics, water condition and other parameters.

Further features include trend analysis of changes over a long period, indicative of small build-ups and early diagnosis of drive or pump problems, all accessible via the UniOP HMI.

The programming is applicable to any pump up to 1.9MW.

It has proved to be particularly effective at critical unmanned pumping stations, typically eliminating any need for call-out resulting from a complete pump jam, significantly reducing maintenance costs.

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