Better predictive maintenance in water pumping

Monitran has helped many water companies to ensure optimum performance and longevity of their pumping systems, through effective vibration monitoring, as Chris Hansford explains

The key criteria for any pump or pumping system in the water and waste treatment industry, either above or below ground, are reliability and longevity.

As submersible pumps and pumping stations are often installed in remote or difficult to access locations, one of the most effective ways of achieving constant optimal performance is through the effective implementation of predictive/preventative maintenance procedures.

The continual drive for increased throughput, be it in water supply or waste treatment, coupled with reduced manpower across the industry, means that the old adage of 'run until failure' is now virtually extinct, as this philosophy, unlike ten years ago, is totally impractical in the modern supply environment.

Most organisations, be it main stream water companies or equipment suppliers, are now firm advocates of predictive/preventative maintenance procedures, with vibration monitoring and analysis being one of the most commonly used methods of assessing pump performance.

This data on pump condition enables the most time and cost efficient decisions to be taken regarding both production schedules and maintenance activity.

Planning budgets and justifications can be supported with factual data and resources can be concentrated accordingly.

As an established supplier of vibration sensors and associated technology to the water industry, with numerous installations on above and below ground pumps and pumping stations, Monitran either directly or though OEM's has helped many water companies to ensure optimum performance and longevity of their pumping systems, through effective vibration monitoring.

In a recent project, for example, a number of its MTN1150W submersible piezo-electric accelerometers were fitted to submersible pumps at depths of up to 100m below the ground.

Typically mounted on the impeller housing, the accelerometers are hardwired back to the surface, to an MTN 3000 switch box, that is situated in an easily accessible location.

The MTN 3000 switch box is capable of accepting input from up to 128 accelerometers, is sealed to IP65 standard and each box is supplied with a custom label indicating plant location and measurement point reference.

A simple data collector can be connected to the switch box, to harvest data for off-line review and analysis.

As with any submersible application, the key criteria for effective performance are a rugged construction and stability below the ground.

A good accelerometer for this type of application, should have a high grade stainless steel casing for corrosion resistance and be fully sealed to IP68 standard.

In installation it is advisable to connect the accelerometer cable to the power cable of the submersible pump, for ease of installation and retrieval should it be required.

In larger or less remote water or waste treatment plants, where higher level SCADA or PLC telemetry systems are in use and typically with a combination of above and below ground pumps and pumping stations, sensors such as the MTN 1186W accelerometer, with 4-20mA output are available, for direct connection into the process control loop.

This enables on-line broad band velocity readings to be taken and trended either locally or remotely.

In addition to vibration monitoring as an effective predictive maintenance tool, the technology also has applications in areas such as impeller balancing to ensure optimum performance, both at installation and at intervals throughout the operational life of the pump.

In essence, balancing is the procedure by which the mass distribution of the pump rotor is checked and, if necessary, adjusted to ensure that the vibration signature of the pump, at a frequency corresponding to the service speed, are within specified limits.

Imbalance can be created by a number of factors, including poor installation, impeller damage and the ingress of contaminants in the impeller chamber.

Effective balancing is crucial to effective pump operation.

The forces of imbalance increase as the square of rotational speed; for example, an impeller running at 3600 rpm produces 16 times as much force as an impeller running at 900 rpm.

The ultimate results being rapid bearing wear and frequent maintenance requirements.

Vibration analysis is the most informative, easy and cost effective of the predictive maintenance technologies.

It is capable of monitoring all moving parts associated with the core rotating assembly of an individual pump or pumping station, helping to identify problem conditions before they become serious and enabling both management and plant engineers to adopt a proactive approach to predictive maintenance procedures.

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