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 Glenfield Invicta for advice on the best valve to use for the temporary supply pipeline. An over-pump arrangement at the dam's top connected to an existing supply pipeline 30 metres below the reservoir level for temporary supply. DCWW's operational parameters were demanding: a maximum pressure of 25 m to enter the existing works, as well as the ability to achieve a range of flow rates up to 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. Because it was critical that pressures greater than 25 m not be 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 valve's allowable limits. As a result, the series 75 concentric butterfly valve was installed.

The valve was installed, and the Glenfield Invicta team was on site to commission it and ensure it was set to the correct position given the flow conditions. Because of the critical role of the valve, a locking device was installed to prevent accidental operation. A locking plate was bolted to the valve's flange, and a stainless-steel chain with a lock was attached to the gearbox handwheel. If the flow rate needs to be changed in the future, the locking device can be removed, and the valve opened to the desired position.

Important considerations

The valve was successfully commissioned. It is now fully operational, allowing the main reservoir construction to proceed as planned. The Alwen Reservoir project demonstrated that butterfly valves can be used for flow control applications and, in some cases, provide more control than alternatives like pressure reducing and eccentric plug valves.

Clearly, the operating conditions for each system must be thoroughly examined to ensure that the proper valve type, size, and specification is chosen. The concentric butterfly valve should be considered when selecting flow control valves for a specific application, especially when relatively low-pressure differentials are involved. When compared to the other valve types mentioned in this commentary, a concentric butterfly valve can provide the required flow control performance while also being more economical, easier to operate, and taking up less space.                          

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, allowing our engineers to specify the best valve for a specific application. Using a supplier with a limited selection poses a risk because it may result in the use of a product that does not fully meet the exact specification requirements.


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