Keeping the water flowing

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 South West Water’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. 

Brendon Teague, South West Water’s condition monitoring manager, knows that the risk of not supplying water to North Devon is one that South West Water cannot afford to run – it is the very reason for the existence of the facility. 

Raw water drawn from the reservoir is pumped to Northcombe Water Treatment Works for treatment by a set of pumps housed below the dam. Five pumps are available for this purpose, though at any given time only one or two might need to be in service. The extra capacity is vital should demand increase, or should any of the duty pumps become unserviceable. 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 for signs of wear or bearing damage. Any damage to the bearing is discovered before it causes a problem. 

Roadford is not the only significant asset that Teague is responsible for, and with over 130 VSE systems in place now at the most important South West Water sites, it has become part of its standard build.  

Most of these systems are connected to the South West Water SCADA WAN, so Teague can view them remotely and see any trends that are developing.

With about 2000 sites overall, South West Water cannot physically monitor all of them at once, so use of the monitoring systems is based on risk. The pumps at Roadford are critical infrastructure, transferring 50 million litres of raw water a day to North Devon. If the pumping station were to fail, the cost of compensation is unthinkable. Also key is pump reliability, or rather the cost of failure of a pump. Replacement can run into tens of thousands of pounds, and there is downtime to consider. 

In each case, accelerometers from ifm electronic 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 LEDs for operators to see if there is anything amiss.

Teague is pleased with the ifm system because the VSE100 also connects into the SCADA system. 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 Teague can keep an eye on all the similar assets from his base, contacting maintenance engineers or visiting the site in person only when the need arises. 

For example, 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 visible from the central office many miles away. Discovering this in good time saved an estimated £40k in repairs.

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, when a pump set is in operation this does not happen in isolation from everything else around it.  On the occasion in question, as a second pump was brought online to match demand, Brendon noticed a change in the pattern from one of the bearings. Inspection showed indentations on the internal bearing raceway, which had not previously been present.  

Vibration had caused energy transfer to the non-running machinery, by chance damaging a stationary bearing. The damaged consisted of 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; but as soon as it came on line, the ifm system proved its worth by detecting the anomaly.

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 Teague, 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. 

As evidence of its satisfaction with the systems installed, South West Water has not only continued to specify ifm on new installations but has been happy to share its experience with other companies in the utility sector, and beyond.