Case

Searching out the best flow control solution

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.

How to choose the optimal valve?

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 right, would have been at threat 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 finally 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.

The valve was fixed and, in order to ensure that it was working as expected, the Glenfield Invicta team were on site to commission the valve and ensure it was set to the correct position given the flow conditions. Due to the critical role of the valve, a locking device was fitted to ensure accidental operation was avoided. A locking plate was bolted to the flange of the valve and a stainless steel chain and lock was connected to the gearbox handwheel. If there is a requirement in future to modify the flow rate, the locking device can be removed and the valve opened to the required position.

Important considerations

The commissioning of the valve was successful. It is now fully operational allowing the works on the main reservoir to proceed as planned. The Alwen Reservoir project has shown that butterfly valves can be used for flow control applications and, in certain cases, can provide greater control when compared to alternatives such as pressure reducing and eccentric plug valves.

Clearly, the operating conditions for each system must be analysed closely to ensure that the correct valve type, size and specification is selected. When selecting flow control valves for a particular application, particularly where relatively low pressure differentials are involved, the concentric butterfly valve should definitely be considered. A concentric butterfly valve can provide the required flow control performance with the added benefits of being more economical, easier to operate, and requires less space compared to other valve types referenced in this commentary.                          

The Alwen Reservoir project is a good example of one of the AVK Group’s promises: “Expect solutions, not just products”

Glenfield Invicta is part of the global AVK Group of companies. This gives us access to an unrivalled portfolio of different valve types and means that our engineers are able to specify the most optimal valve for a particular application. There is a danger in using a supplier with a limited selection, as it can sometimes lead to the use of a product that doesn’t fully meet the exact specification requirements.

                     

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