Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/516873
16 WET NEWS JUNE 2015 Carrying out maintenance or inspections on service reservoirs can be a complex process. The challenge: Isolating reservoirs without stemming the flow INSIGHT ValVEs, driVEs & aCtUators Northumbrian Water likes its treatment works, such as Wear Valley WtW, to operate at steady flows to ensure the most efficient results THE CONCEPT • the new rCBV negates the need for a separate reservoir bypass valve and is always clean • No manual entry to the reservoir is required, thus minimising the contamination risk • the bypass can be regularly operated to condition and turn over the bypass main leaving it clean to be used whenever required • the rCBV can be remotely altered to run as a flow control valve or a PrV NEED TO KNOW 1 the reduced visits to site and reduction in materials used saves on fuel and carbon consumption 2 Manual access into a service reservoir can cause safety and water quality issues 3 traditionally a separate bypass valve would be installed and operated when the reservoir needed cleaning. 4 Under the old system the reservoir would have to be isolated and then drained. THE VERDICT "if we hadn't created this type of bypass it would have meant any work on that reservoir could only have been done at certain times of the year, for instance outside of high demand periods. "it gives us the flexibility to carry out future work with minimal impact to operations" Mark Pledger, Northumbrian Water I n the North, Northumbrian Water has in excess of 220 service reservoirs, providing a number of different uses. Some are predominantly used for breaking pressure and/or strategic storage for network resilience, or eliminating variation in demand. Wherever possible the company also likes its treatment works to operate at steady flows. "That's how we achieve the best water quality and most efficient results, when they're running at a stable flow," says Mark Pledger, Northumbrian Water senior technical advisor, strategic networks. So with the control and operation of service reservoirs being a complex procedure, taking the reservoir out of service for inspection and cleaning adds to the dilemma of ensuring minimal impact on customers. Many service reservoirs have ball valves as inlet control mechanisms, and manual access into the reservoir is required for maintenance, causing potential safety and water quality issues. Normally, the reservoir would have to be isolated and then drained. The reservoir would be available for access but this would be considered as a confined space so it would need to be inspected and the suitable safety precautions taken. Scaffolding would be erected to enable direct access to the valve and then maintenance carried out. Once complete, the scaffolding is removed and the reservoir is cleaned and chlorinated. This process can take up to two weeks. Northumbrian had a particular engineering issue with two of its service reservoirs – Frosterley and Brandon. Pledger explains: "Most of our reservoirs are two compartments with an external valve or independent control to each side, but these have three one of which being a combined inlet control. "The inlet flow into the reservoir came through the first compartment where the original control valve was. It was a A solution: A RCBV valve gives flexibility a valve combining the roles of a reservoir inlet valve and bypass valve has potential to fill multi purposes. N orthumbrian Water, in conjunction with IVL, has developed the Reservoir Control and Bypass Valve (RCBV) where the reservoir inlet valve and bypass valve have been combined to create a single control version that serves both purposes. The prototype has been in operation at three sites within NWG for more than a year, and was conceived by placing the control valve far enough upstream of the reservoir inlet to allow the modification to the bypass pipework. Under normal operation, the flow into a service reservoir is controlled by an Electrically Operated Valve (EOV). As this control valve is situated outside the reservoir, maintenance can be conducted without the need for manual entry into the reservoir and, if required, a conditioning flow can be leš on the bypass. During bypass operation, the reservoir bypass is opened and the inlet to the reservoir is closed. The Pressure Reducing Valve (PRV) setting reflects the pressure that would normally be expected on the reservoir outlet. The RCBV is placed outside the reservoir structure and replaces the mechanical ball valve situated on the inside of the reservoir. The RCBV can be remotely altered to run as a flow control valve or a PRV. Whilst the reservoir is in service the RCBV operates as a reservoir inlet valve. The valve can be set to respond to reservoir level, flow set point or telemetry control. When the reservoir is taken out of service for cleaning or maintenance the RCBV will operate as a PRV and provide a source with a pressure equivalent to reservoir head. Using the RCBV, valve maintenance is carried out by one person in two to four hours. With the RCBV now situated outside of the reservoir no manual access into the reservoir is required for maintenance, reducing manpower, working time and accident risk and eliminating water quality issues. The immediate savings are obtained by using only one control valve instead of two. The cost of the control valve installed at Northumbrian Water's Frosterley Break Pressure Tank was £12,500, for instance. Mark Pledger, senior technical advisor, strategic networks, at Northumbrian Water, says: "It's difficult to quantify the payback because it allows us to do work without restricting the timeframe of when we can do it. If we hadn't created this type of bypass it would have meant any work on that reservoir could only have been done at certain times of the year, for instance when we didn't have high demand periods. It gives us the flexibility. "The basic cost saving is through not having an extra control valve and not having to have an operator stood there for the duration while the reservoir is out of supply for cleaning." Pledger concludes: "It also allows us to continue to keep our flows from the treatment works going at a stable flow rate. We don't have to restrict the flow while we're cleaning the reservoir." submerged control valve operating in the inlet chamber. This is potable water so working in this environment is not ideal from a water quality perspective; it's not great from a health and safety perspective because it's a reasonably deep structure; and the valve was coming to the end of its working life so we needed to replace it." The solution was to isolate the reservoir inlet chamber, which meant isolating the whole reservoir. The two reservoirs serve two purposes in that they provide strategic storage, and are also break pressure tanks. "We could have gone with a standard type control valve which would control the reservoir, but we'd then need to bypass the reservoir in order to keep supplies going down downstream whilst we had it isolated. The next question is 'how do we do that?', says Pledger. The answer came in the shape of a Reservoir Control and Bypass Valve (RCBV).