Roadford Lake is key to South West Water supplying raw water to the region around Exeter and beyond. The reservoir at Roadford is now the largest area of fresh water in the southwest of England covering 730 acres of water (8,140 million gallons of water) and is also the largest and most recent reservoir in the SWW region. Completed in 1989, the reservoir was considered necessary after the droughts of 1976 and 1984, in order to guarantee continuity of supply. Today, 90% of SWW’s supply comes from surface water sources, such as reservoirs and river intakes, and the three large strategic reservoirs, at Colliford and Wimbleball and Roadford form the bulk of that resource.
The importance of Roadford, specfically the continued supply of water from it, is the main reason why Brendon Teague, South West Water’s Condition Monitoring Manager, chose to fit vibration monitoring equipment from ifm electronic. Brendon knows that the risk of not supplying water to North Devon is one that SWW cannot afford to run – it is the very reason for the existence of the facility.
Water drawn from the reservoir is pumped into the delivery system by a set of pumps housed below the dam. In total, five pumps are available at Roadford for this purpose, though at any given time only one or two might be required to be in service. The extra capacity is vital should the demand increase, or should any of the duty pumps become unserviceable. With that in mind, the engineers at South West
Water need to ensure that each pump, and each pump motor, is kept in the best possible condition. So for this reason the ifm electronic vibration monitors are fitted to the motor and pump bearings. The system continuously measures the level of vibrations at each measurement point and monitors these levels for signs of wear. Any damage to the bearing is discovered before it causes a problem. Roadford is not the only significant asset that Brendon is responsible for, and with over 130 VSE systems in place now at the most important SWW sites, it has become part of their standard build.
The majority of these systems are connected to the SWW SCADA WAN, so Brendon can keep an eye on them. Brendon knows that such situations develop over time, so he likes to be able to see the trend. With around 2000 sites overall, SWW cannot physically monitor all of them at once, so use of the monitoring systems is based on risk. That is why Roadford is a key, high risk installation as it provides 50million litres/day and is the only site providing raw water to North Devon – the cost of compensation if it were to fail is enormous. Also key is pump reliability, or rather the cost of failure of a pump. Replacement can run into be tens of thousands of pounds, and there is downtime to consider.
In each case, accelerometers from ifm are fitted in critical locations; these are typically at the non-driven and driven ends of the motor shaft and of each pump, and also in the ‘plummer block’ bearing where there is a longer shaft connecting motor and pump. Four accelerometer signals are initially fed to the local VSE100 monitor where the evaluation takes place. Each local panel housing the monitor has a quick reference explaining the LED’s for operators to see if there is anything amiss. Brendon is particularly pleased with the ifm system, however, because the VSE100 also connects into their SCADA. This means that first thing every working day he can check the signals from his desk in Exeter, about 30 miles distant. Roadford is not the only installation of its kind, so Brendon can keep an eye on all the similar assets from his base, contacting the responsible maintenance engineers or visiting the site in person only when the need arises. The need has arisen on more than one occasion. Not only do the ifm systems monitor the bearings of motors and pumps that are running, they have also detected damage to a bearing that was not in use at the time, and on another occasion picked up an issue with a seal on a centrifuge.
Centrifuges have been used for the dewatering and thickening of sewage sludge in waste water treatment since the 1930’s. Such valuable equipment needs careful monitoring as much as any pump, so accelerometers were fitted to the centrifuge bearings. Over a period of days, it became clear that the vibration trend on the non-drive end bearing of one centrifuge was showing an aberration, which quickly became a big jump in the acceleration, indicating failure. Investigation showed that the seal had failed, allowing sludge to enter the bearing. This was all visible from the central office many miles away. Discovering this in good time saved and estimated £40k in repairs.
The incident with the pump that was not in use is also interesting. As sites like this are not always manned, or are manned by staff who have many duties, so cannot constantly be aware of every shaft or bearing, the usefulness of such a system becomes clear. On one notable occasion the duty aggregate was running and observation of the vibration signals from the pump and motor showed everything as normal. However, the continuous monitoring of all units brought to light a discrepancy. Even though the standby systems were not in operation, the vibration monitoring was still connected. Brendon noticed a change in the pattern from one of these bearings. The unit needed to be checked before being relied on.
Further inspection showed indentations on the internal bearing raceway. Vibration had been transmitted to the non-running machinery, by chance damaging a stationary bearing. This was caused by the phenomenon known as ‘brinelling’ (or rather false brinelling) where a metal component striking another causes surface indentation. [Brinelling is named after the Brinell scale of hardness, in which a small ball is pushed against a hard surface at a preset level of force. The depth and diameter of the mark that is left indicates the brinell hardness of the surface.] As the unit was not running, this might have gone unnoticed, resulting in premature failure of the bearing. ifm electronic offers a variety of vibration monitoring solutions, from simple sensors to the fully networked diagnostic systems employed at South West Water.
According to Brendon, the savings brought about by using the ifm system are not inconsiderable – that is counting his time travelling from site to site to take direct readings in addition to saved downtime. Not to mention the financial savings covering not just hardware and secondary damage, but also potential losses though fines and even compensation claims. This is backed up by the fact that by using the ifm system South West Water have avoided catastrophic issues for some eight years and continue to implement ifm product on new systems.
Belief in the system is also a factor; personnel have grown to trust the ifm system, and it is never accused of ‘crying wolf’. On the contrary, it has been praised by staff for “picking up problems before they could hear it”, and thereby saving the day.
All in all, SWW believe this is a modern approach to managing their assets, for “Providing the information to have a more informed view” as Brendon says. As evidence of their satisfaction, South West Water have not only continued to specify ifm on new installations but have also been happy to share this experience with other companies in the utility sector, and beyond.
Acknowledgements: Thanks to Brendon Teague, Condition Monitoring Manager, South West Water for his assistance in this article.