Plant and maintenance engineers seem to have a sixth sense about conditions which lead to pump failures the ability to correlate a fluctuating pressure gauge reading, a slightly different pump noise, a series of small indicators which can be enough to tell them there is trouble round the corner. But with the days long gone when every engineering scheme would include 100% standby plant, and the results of any failure consequently more serious, this is no longer enough.
Yorkshire Water has more than 2,000 pumping installations to move water, sewage and sludge around the county and over 10,000 installed pumps, many of them critical to its operations. The company needed a system which embodied that sixth sense.
A Malvern-based company, ISA Developments, has come up with just that kind of diagnostic technology in an affordable format suitable for the range of industries which use pumps and compressors, and probably many more.
Called Aim acoustic emission technology for intelligent pump monitoring its origins are in detecting fatigue crack growth in aviation. The founders of the company, Andrew Wilkins and Richard Czaja, developed their techniques for monitoring vibration in helicopters.
Czaja, technical director, explains: ‘To date, condition monitoring has relied primarily on the application of vibration monitoring techniques to identify and quantify faults in machines. But it has relied on expensive fast Fourier transform processing and a high level of operator skill. Acoustic emission monitoring is simpler to carry out and is superior for detecting problems arising in slowly moving or reciprocating machinery such as pumps and compressors.’
The theory is simple. A new healthy pump should produce an acoustic profile that correlates with good performance. This profile is adjusted to incorporate the characteristics of the pump type and the media being pumped. As pump wear becomes apparent, the profile will change.
Aim monitors and logs operational parameters such as power, flow, pressure and speed in combination with acoustic emission sensors used to measure mechanical wear and tear and identify lubrication problems and cavitation.
An algorithm developed by ISA provides an overall indication of pump performance based on the logged information and the pump profile.
This pump performance index is a value between 1 and 10 the higher the number, the closer the pump is performing to its initial value. The plant maintenance engineer just has to look at the LCD on the pump being monitored to see how it is performing.
Aim contains a powerful datalogger which is capable of storing months of measured and calculated pump performance data using a PCMCIA card and providing a range of communication options for transferring historical data to a host computer, Scada or Telemetry system for further offline analysis.
It has already started to save money for Yorkshire Water. It averted a bearing failure on a large screw pump used for pumping raw sewage at its Knostrop sewage treatment works. If the bearing had failed the damage would have led to repair and replacement costs of around £20,000.
But Aim detected a significant change in the pump performance index which led to the top bearing being stripped down. The maintenance team was initially unable to locate any physical evidence of a problem, but a detailed investigation by the National Tribology Laboratory identified serious fatigue damage to the bearing components.
Following the success of the Aim system at Knostrop, Graincliffe water treatment works was selected to extend the system to different pump types and to ensure that it could be fully integrated with Yorkshire Water’s telemetry, IT and report generating systems.
Here the Aim system is installed on critical items of plant such as chlorine dosing pumps, aeration blowers and recirculation pumps. This site is only staffed during normal working hours, so a system that alerts the plant operators and maintenance to impending problems has proved extremely valuable.
Yorkshire Water has installed 10 Aim systems on critical pumps and plans are in hand for a further three to be installed on inaccessible pumps, such as submersibles and those in bore holes.