For a reservoir project in Wales, Glenfield Invicta’s team of experts rise to the challenge to find the most optimal valve and flow control solution
The Alwen Reservoir is the largest man-made ‘lake’ in Wales, covering some 900 acres. Located 14 miles south-west of the market town of Denbigh, the reservoir was constructed between 1911 and 1920 to provide water for the town of Birkenhead on The Wirral.
Lewis Civil Engineering, based in Pontyclun, South Wales, is leading a refurbishment project at Alwen Reservoir for Dwr Cymru Welsh Water (DCWW). A vital element of the enabling works was the creation of a duplicate water supply arrangement as the existing mains were to be shut off whilst work was being carried out on the reservoir.
Searching out the optimal valve - how?
Lewis Civil Engineering contacted the team at Glenfield Invicta for guidance on the optimal choice of valve for the temporary supply pipeline. The temporary supply involved an over-pump arrangement at the top of the dam connecting to an existing supply pipeline 30 m below the reservoir level. The operational parameters stipulated by DCWW were challenging; a maximum pressure of 25 m to enter the existing works combined with the ability to achieve a range of flow rates with a maximum of 462 litres/second.
The natural choice for this application would have been a pressure reducing valve. However, due to the small differential pressure requirement of 5 m, the pressure reducing valve (PRV) would have been working close to its limit. As it was critically important that pressures in excess of 25 m were not introduced into the existing infrastructure, an alternative control valve solution was required.
Demonstrating engineering expertise
Glenfield Invicta analysed the application in detail, and considered using eccentric plug valves, needle valves and butterfly valves. The eccentric plug valve - like the pressure reducing valve - would also be operating close to its limit. The needle valve, although it would have been suitable, would have been at risk of becoming clogged due to the raw water passing through it; the needle valve has a smaller internal flow path and, when an anti-cavitation device is added which has additional smaller slots, any twigs, stones or solids may become stuck, and it could ultimately clog over time.
The Glenfield Invicta engineering team therefore considered whether a series 75 concentric butterfly valve would meet the operating criteria. To accommodate the range of specified flow requirements at the available pressures, a series 75 concentric butterfly valve (DN450) would be operating within a range of 35% and 45% open position. This is well within the allowable limits for this valve. Consequently, it was decided to install the series 75 concentric butterfly valve.