Water & Wastewater Treatment

44 | JUNE 2014 | WWT | www.wwtonline.co.uk In the know Getting to grips with gearboxes Extending the life of key equipment Gearbox design delivers savings for wastewater applications G earboxes are used throughout the wastewater industry; in pumping, filtering, settlement, thickening and aerating equipment. The gearboxes are oen located in remote locations or as part of large outdoor processing sites; and as such are expected to perform reliably to avoid time-consuming maintenance requirements. However, even the best components have a finite life expectancy and eventually need to be replaced. It is during replacement that it is important to consider how different designs may improve efficiency, maintenance commitments, and fit within the original footprint. Many sewage treatment works (STW) have a range of ageing assets Jim NortoN TEchNical MaNaGEr BrEviNi which will be under review for repair or replacement in order to maintain the required levels of operation. Failure of these assets can result in serious consequences, such as increased levels of certain chemicals in the final effluent which is returned to the local watercourse. This can trigger a non- compliance charge from the Environment Agency (EA) which oen results in a significant fine for the utility company operating the sewage treatment works. The choice which usually faces the site manager when an asset reaches the end of its expected lifespan is one of repair or replace; a common dilemma experienced by maintenance engineers across the globe. In this environment, where reduced running costs and improved efficiency is paramount, replacement is usually seen as the better option. However, replacing a gearbox on an ageing piece of equipment could entail a lengthy project to redesign the asset in order to accommodate the new gearbox. In terms of gearbox design, choosing a planetary arrangement offers increased reliability with a higher efficiency and reduced size and weight. Typical efficiencies of the planetary unit are 98% per stage, ensuring that the energy being generated is not being consumed by mechanical losses. The knowledge that a single stage planetary gearbox unit is around 98% efficient, even at very low speeds, can be useful, "Planetary gearboxes are designed specifically for arduous, continuous applications such as those in the wastewater industry." Jim Norton especially when compared with some traditional worm gears where efficiency can be as low as 50%. Planetary gearboxes are designed specifically for arduous, continuous applications such as those in the wastewater industry. The planetary design has inherent advantages over conventional helical gearbox designs because there is an equilibrium of forces on individual gears; so the planet-carrier is in charge of transmitting torque only. Conventional helical gearboxes employ a system of bearing- supported, gear-carrying shas where forces are concentrated. Planetary gearboxes have a complete gear system that is in-line, so there are no high torsional loads on the bearings and gear elements. For further reading please go to wwtonline.co.uk

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