Water and Effluent Treatment Magazine
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10 WET NEWS APRIL 2016 A staggering 3.36 billion litres of drinkable water is lost every day in the UK due to leakages. Equating to 40 litres per customer per day, leakages are o•en the result of inferior valves, major pressure surges and a declining overall pipe network. As pressure mounts on the water industry to provide a more sustainable and efficient service, finding solutions to minimise pressure surges, moderate flows and promote calm networks is becoming a priority. Water leaks have become a major sore spot for water companies and significant investment has been made to improve pipe systems and minimise leakages. In spite of this, there has only been an 8% improvement in water loss over the past ten years. Leakages o•en occur when there is a sudden change in water velocity, causing pressure to build up in the pipeline. The surge in pressure can be so forceful that it ruptures pipes, puts pressure on pipe joints and its impact can cause lasting damage to the overall network. Shockwave Known as 'water hammer', this problem can be caused by a valve within the pipe system closing too abruptly. Completely shutting off a pipe suddenly will cause a moving Under pressure • The UK water system is facing a tsunami of damages if it does not act fast, warns Talis UK's Mark Hodgens. ONSITE LeAKAge MAnAgeMenT body of water to hit or 'hammer' the valve at force and then be pushed backward, creating a shockwave. This change in velocity is what leads to high pressure. If powerful enough when passing through bends within the pipe system, the shockwave can create enough pressure to forcibly move the pipe off supports and cause further damage to the surrounding area. Closing valves suddenly can also lead to cavitation and pipe networks are extremely vulnerable to the severe damage this can cause. When a valve closes abruptly, pressure can fall downstream to a level which causes a mass of water to effectively boil. The boiling water will produce bubbles which then form a vapour cavity. When the pressure normalises, the bubbles burst and can cause spikes of intense pressure of up to 10,000bar to form. Serious damage from this cavitation will ensue if the spikes of increased pressure come into contact with a pipe wall or valve body. Both water hammer and cavitation are regarded as serious threats and have caused severe levels of damage to the UK pipe network over the years. Even in the face of millions of pounds of investment and countless hours spent repairing pumps and pipelines, the catalogue of problems caused by these two projEcT SpEcS • Reduce water leakage • Minimise 'water hammer' and cavitation destructive forces include the rupture and the collapse of valves and even whole pipelines. Damages Increases in water pressure occur quite regularly in the water system, and changes in pump conditions or valve positions commonly alter water velocity. However, when an increase in pressure is minimal or controlled, the velocity of water undergoes more of a gradual change meaning that while water hammer is still happening, it is virtually undetectable. It is only when this pressure builds to the extreme that pipe supports may exceed their maximum capacity and incur damages. Shortening the life of the pipe systems, this damage can come in the form of bent or broken pump sha•s, damaged impellers, distorted and deformed valve discs, and cracked or broken mains – all of which will ultimately increase the likelihood of leakages. Fortunately, the UK water industry has options and there are effective means to minimise the effects of water hammer and cavitation and reduce water leakages. The common denominator with both water hammer and cavitation is sudden changes to water pressure, which are o•en the result of the rapid shutting of valves. With this in mind, the way in which a valve operates must be carefully considered Valves that regulate opening and closing speeds will make any changes in pressure less drastic. One such example is the fully WRAS approved ERHARD ROCO wave Butterfly Valve which offers a slider-crank mechanism (SKG) gearbox, facilitating a two-step shutting mechanism. Closing 70% of the way quickly and then drawing out the closing of the remaining 30% at a much slower rate, the ROCO wave Butterfly Valve works to slow down the momentum of water and mitigate the impact of water hammer. Additionally, its curved wave shape allows for a so• and seamless opening and closing, without resistance. Benefitting from a polygon connection between the tilting disk and the sha•, the valve is continuously protected against corrosion. The polygon shape also means less force or torque is required to open and close the disk, leading to reduced costs especially where the valve is actuated. The valve comes with two disc designs – ERHARD's 'Skeleton' butterfly disc is suited to larger valves with higher pressure ratings and acts to stabilise and optimise flow performance. For valves with smaller diameters and lower pressure ratings, ERHARD's principle wave disc