Glenfield Invicta, an AVK company, has specified, designed, fabricated and installed three Series 856 submerged discharge valves at Southern Water’s Bewl Reservoir.
Background
Bewl Reservoir sits on the Sussex/Kent border some ten miles east of Royal Tunbridge Wells. Completed in 1975, Bewl Reservoir is the largest body of inland water in Southeast England.
Project Scope
Southern Water is investing over £30m to improve reservoir management at Bewl. In particular, it has installed three hydraulic syphons in the 1800m long dam wall to facilitate a more rapid, more controlled drawdown of reservoir water levels.
The syphons feed water through pipes located on the 20m high reservoir wall down to the three submerged discharge valves sited at the base of the wall. The role of the valves, submerged in an open discharge chamber, is to dissipate the kinetic energy (see inset panel) in the water enabling the water to flow gently over the walls of the chamber into downstream watercourses.
Glenfield Invicta was asked by Southern Water to specify, design, build and install the three submerged discharge valves.
Specification and Design
With drawdown projects such as that at Bewl Reservoir, it is hugely beneficial for Glenfield Invicta’s engineers to be involved from the initial stages. Early engagement optimises the engineers’ ability to review all valve options and develop an optimal solution.
For Bewl Reservoir, the consulting engineers provided Glenfield Invicta with the flow and pressure conditions under which the selected valves would be expected to operate.
Detailed consideration was also given as to how the submerged discharge valves would be operated. Given the requirement for the valves to open and close quickly in order to deliver a rapid and effective drawdown capability, linear hydraulic actuation was specified rather than the more standard rotational electrical actuation.
Although the Series 856 submerged discharge valve is based on fundamental hydraulic and mechanical principles, the overall length and the port geometry of the specified valves are unique for each application as they have to meet a particular set of project-specific system parameters. Furthermore, in the case of Bewl, the sheer scale of the valves meant that every significant component had to be individually designed and manufactured.
Build and Test
The valves were designed and assembled at Glenfield Invicta’s workshops in Kilmarnock. The majority of the valve body consists of a series of ductile iron castings and pipe sections. The valve outlet was fabricated in aluminium bronze. The hydraulic cylinder that controls flow rates through the valve is stainless steel. All materials and coatings used in the build of the valves are WRAS approved. With the client in attendance, the valves were hydraulically tested in the workshop using a portable hydraulic unit. With each valve measuring 8.25m in height, the hydraulic test had to be undertaken with the valve on its side. Mobile cranes were brought in to lift the valve sections on to the low loader for transport to site. Great care was taken to ensure the valve was located in the optimal position to distribute load over the five axles of the transporter during transit.
Valve Installation
A team of Glenfield Invicta engineers undertook the installation of the three valves on site. The client was responsible for arranging craneage.
Lifting eyes were designed into the body of the valve’s inlet casting. When combined with the skills of the crane operator, slingsman and engineers, this ensured a safe and accurate lift as the valves were located within the tight confines of the discharge chamber.
To eliminate the risk of damage, the valves were installed without their 3.7m long double acting hydraulic cylinders which locate directly on to the top of the valve. Varley Hydraulics was Glenfield Invicta’s hydraulic sub contractor on the project, supplying both the hydraulic cylinders and the hydraulic power units.
As the hydraulic syphons and submerged discharge valves are a safety measure to accommodate extreme weather events, there is a strong possibility that they may never see active service. However, to ensure they operate effectively if called into action, the system will be exercised and put under stress once every twelve months. Final commissioning is expected to be completed in April 2026.
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