Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | OCTOBER 2016 | 35 Mick Burton KEy ACCOunT MAnAgER JACOpA Protecting Your Pumps With pumps being among a water company's most critical assets, screens and automated trashrakes have a vital role to play in avoiding damage and costly repairs In the know Getting to grips with... pump screen protection This Bosker trashrake system is an example of pump protection in action F or water companies faced with the need to closely manage costs while maintaining high levels of service, providing protection for vital pumps is a key issue. Debris from storms or from dumped material can cause significant damage and blockage, leading to long periods of downtime while repairs are carried out. Pumps at water and wastewater treatment works can cost £200,000 or more, so protecting them is critical. What particular challenges do water companies face? One of the worst scenarios that a water company can face is the discovery that a critical, major pump has been wrecked by debris, either from storms, or waste that has been inconsiderately dumped. The range of floating debris that enters treatment works intakes is extremely varied, so all treatment works routinely employ a range of coarse and fine screening to ensure that the key downstream pumps and processes are well protected. Which assets need to be protected and how? Typically, first in the 'firing line' are the very large, system-critical pumps at inlet works, either centrifugal models which are used to abstract raw water (at water treatment works) or centrifugal, screw and other designs employed to transfer raw wastewater from the deep intakes at wastewater treatment works. Later in the sewage treatment process, other pumps including positive displacement, rotary lobe and progressive cavity pumps can also suffer blockages and damage from unscreened or poorly screened sewage. What methods are available? Raw water intakes o‡en employ manually raked coarse bar screens as primary protection devices typically with bar spacings of 100mm or more, but as the first line of defence they frequently become clogged and require regular cleaning. In the past, this meant operators had to intervene manually to remove debris, a duty much disliked by operatives. However, automation is now available to assist which is safer and more efficient. Many treatment facilities have therefore adopted mechanically automated and cleaned bar screens which in addition to avoiding the much hated manual cleaning have a higher screening capture rate with improved flow conditions through the screen. At sewage treatment works and sewage pumping stations, chain raked bar screens may be fitted as an alternative. However, such designs o‡en struggle to remove large and awkward debris such as rag, fat and other larger debris which collects at the screen and can put extreme load on the equipment causing it to overload or fail and require manual intervention.