Water & Wastewater Treatment

POTABLE WATER TREATMENT & SUPPLY 21 March 2014 Water & Wastewater Treatment wwtonline.co.uk R outine checks of a raw water valve at a water treatment works (WTW ) in Wales revealed cavitation causing extensive and potentially fatal wear to a strategic flow control valve. Further investigations of the 'pin holes' by non- destructive testing of the valve at Dŵr Cymru Welsh Water's Pontsticill WTW near Merthyr Tydfil found that in less than five years, cavitation had put the valve in danger of imminent failure. Should the valve have failed completely, the works would have flooded and reinstatement would probably have taken several days, placing 70,000 customers at risk of losing supply. Although there was a replacement plug valve on hand, Dŵr Cymru Welsh Water (DCWW ) sought advice from valve specialist IVL Flow Control as to the suitability of this type of valve in this environment. On studying the available data, it was proved that the pressure differentials present could not be handled by this type of plug valve, and it would inevitably lead to a repeat of the cavitation problems and another potential loss-of-supply situation. IVL recommended a series 300, 600mm EOV control valve as an alternative, along with a technical assessment, which DCWW was happy to accept. Installation The difficult replacement was carried out overnight, and the removal of the existing valve and re-installation of the new valve was achieved within an eight-hour overnight shutdown period between 8pm and 4am, with IVL's engineers on hand to assist. Chris Holloway, production asset engineer at DCWW said, "We had noticed a problem with the old valve when we were carrying out regular checks of the raw water valve. There was water spraying out of very small holes in the valve body. "When it came to changing the valve - and the capital team told us they were going to change the type of valve - I was a bit concerned that that the operation of it would change and we would not be able to restart the works in the way we normally would. "On the night after the new valve was installed and everything was ready to go, we decided to try to bring on the works using the normal method, where we have to bring the flow on very quickly for the first 40ML/d, to make sure the DAFs [wastewater clarifiers] get a decent flow to start with. I was surprised that the flow came on so smoothly and did exactly what I was hoping it would do. All changes following this were much smoother than we were getting with the old valve." IVL says the new 600mm control valve at Pontsticill WTW is already showing that it is resistant to cavitation, performing within an accuracy of ±0.5% and controlling flows up from 'closed' to around 95Ml/d. The supplier says that in this application, the new control valve will have a lifetime of 20-30 years when serviced and maintained regularly. nnn Pin hole cavitation revealed the unsuitability of a valve installed at a treatment works in south Wales. IVL Flow control's director, Craig Stanners, explains how a replacement was selected Valve replacement averts flood risk Perspectives Client "The detailed planning, competent risk assessment and above all, leadership and teamwork to get the job done in such a short space of time overnight is highly commendable. The commitment, proactive approach and long-term solution for this essential work have been first class." Peter Perry, chief operating officer, DCWW Operator "Since the install of the new valve we have noticed that the changes to the flow required by network and the high-lift pumps, which can be as much as 20Ml/d at any one time, have been a lot smoother than before. The control of the chemicals, which are flow-paced from the front-end, has also improved enormously." Chris Holloway, production asset engineer, DCWW Supplier "Thankfully this type of work goes unnoticed by the general public, but when dealing with such large volumes of water from a health and safety and water quality point of view, the planning and effort that goes into ensuring a smooth transition has to be absolutely meticulous. This was a great example of teams working together to protect essential services and an excellent example of a positive intervention that will benefit both customers and the company." Craig Stanners, director, IVL Flow Control The new EOV control valve installed

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