The importance of giving off good vibrations
Chris Hansford of Monitran, looks at the role vibration monitoring has to play in reducing the cost of maintaining both pumps and pumping systems, and ensuring that they are able to operate efficiently.
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 reductions in manpower across the industry, mean the old adage 'run until failure' is now virtually never adhered to. Unlike ten years ago, the current industrial climate makes this philosophy almost totally impractical.
Most companies, be they water companies or equipment suppliers, are now advocates of predictive/preventative maintenance procedures, with vibration monitoring and analysis being one of the most commonly used methods of assessing pump performance.
Vibration monitoring data can do a great deal to help those in charge of pumps and pumping systems make time and cost-efficient decisions when looking at both operation schedules and maintenance programmes. Such information can be a useful tool when it comes to planning budgets, allocating human resources.
With numerous installations on above and below ground pumps and pumping stations, Monitran is an established supplier of vibration sensors and associated technology to the water industry. Either directly or though original equipment manufacturers (business which integrate Monitran products with their own or other equipment), the company has helped many water companies to try to attain optimum performance and longevity for their pumping systems through effective vibration monitoring.
In a recent project, for example, a number of Monitran MTN1150W submersible piezo-electric accelerometers were fitted to submersible pumps at depths of up to 100m. Typically mounted on the impeller housing, the accelerometers are hardwired back to a MTN 3000 switch box sited on the surface.
Capable of accepting input from up to 128 accelerometers, the MTN 3000 is sealed to IP65 standard and each box is supplied with a custom label carrying information such as 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 rugged construction and stability below ground. For this type of application a good accelerometer should have a high-grade stainless steel casing for corrosion resistance and be sealed to IP68 standard.
During installation it is advisable to connect the accelerometer cable to the power cable of the submersible pump. This makes installation easier and, should it be required, retrieval.
In larger or less remote WTWs or STWs, where higher level Supervisory Control And Data Acquisition (SCADA) or programmable logic controllers (PLC) telemetry systems are in use, 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 online broad-band velocity readings to be taken and trended either locally or remotely.
As well as being an effective predictive maintenance tool, vibration monitoring has applications in areas such as impeller balancing which helps 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 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. Correct balancing is crucial to efficient pump operation. The forces of imbalance increase as the square of rotational speed; for example, an impeller running at 3,600rpm produces 16 times as much force as an impeller running at 900rpm. Ultimately, imbalance results in rapid bearing wear and the need for more frequent maintenance.
Vibration analysis an informative, easy-to-undertake and cost-effective predictive maintenance technology. It can monitor 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, enabling management and engineers adopt a proactive approach to predictive maintenance.