Water & Wastewater Treatment

14 The PumPing STaTion - PumP and ValVe SuPPlemenT 2016 In Depth: Valves and Leakage Naturally, components within the water network will weather during their lifetime and can be corroded by materials around the pipe such as soil and water. Further causes of leakages can occur particularly in the winter months. During extremely cold periods, pipes can freeze and will expand to make way for the frozen water. As the pipe is stretched beyond its limits, it could burst and the ensuing break would then allow thawed water to leak. Leakages can also occur when accidental damage is caused to the pipe network. For instance, the vibrations from traffic travelling on the roads above could weaken the network. Also when workers are digging up the road to carry out maintenance work on the transport network, accidental damage to pipes can be caused. Why water hammer is a cause for concern Water hammer is one of the main causes of leakages and can be the result of a valve being closed too quickly. It occurs when the valve shuts but the water in the pipe is still moving. As the moving water hits the closed valve, it causes a shockwave to ripple backwards along the pipe. When this happens, the change in water velocity causes pressure to build up which unfortunate- ly can cause leaks. Leaks and pressure surges caused by water hammer can cause serious damage, including ruptures to the network. In some instances, it has been known to crack or burst water mains, put stress on pipe joints and sealing methods, bend pump sha-s, deform check valve disks and even move the pipes off its supports: damage that ultimately brings he-y repair costs to the water industry. If the network is damaged like this, the overall life of the system will be shortened and could even lead to leakages happening more o-en. At present, it's estimated that each water company is already losing one in five of every litre of water gathered, cleaned and treated through leakages. So in order to promote a more sustainable and efficient network, this issue requires urgent attention to find a viable solution. How can the issues be resolved? At times, changes in pressure and water velocity will occur and conditions around the pipes and surrounding environment will not remain constant. When changes are made to the network, such as if a valve position is altered, this could result in small, gradual pressure changes that are usually undetectable. Water hammer becomes a major issue when these pressure changes are not small, and when a valve is shut too quickly. Therefore, a possible solution to prevent this would be to control the closing speed of the valve to ensure that any resulting pressure changes are less abrupt. One product that has been developed to regulate the closing speed of the valve is the WRAS-approved ERHARD ROCO wave Butterfly Valve. Its slider-crank gearbox (SKG) prevents pressure surges and manages the valves opening and closing speed. Offering optimum precision, it closes the first 70% of the valve quickly, with the last 30% closing slowly to prevent disruption to the efficient flow within the pipeline and promote a 'calm network'. This slows down the overall speed of the close, consequently reducing the speed of the flowing water so that changes to the pressure will be more gradual. Wave design The 'wave' design of the disk reduces resistance and optimises flow by ensuring that the valve is closed smoothly. ERHARD's new 'Wave' butterfly disc has been designed to enhance flow performance to offer a more energy efficient isolation valve solution. Alongside this, the patented polygon connection between the sha- and disc provides optimum corrosion protection to guarantee clean potable water, resulting in safe operation throughout the entire life of the valve. This polygon connection proves to be a more positive drive force with no need for pins which could be an avenue for corrosion. This will also reduce the amount of torque required to operate the valve therefore decreasing actuation cost. Overall, the valve helps to prolong the life of the whole network as its high quality coating and reliable seals provide long-term protection against corrosion and leakages. Calming the network Reducing the pressure on the water system needs to remain a top focus for the UK's water industry in order to reduce leakages and provide a more efficient service. Implementing pressure management measures will help to look a-er water distribution systems in the long term, while also reducing costs. This not only benefits the network by reducing maintenance and operational costs and losses in revenue, but also eases the financial burden on the customers who are ultimately footing the bill. The ROCO wave valve, semi-open (left) and open showing the slider crank mechanism (right)

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