Water & Wastewater Treatment

32 | AUGUST 2015 | WWT | www.wwtonline.co.uk In the know Getting to grips with... mechanical seals What are the most common reasons that seals fail? A common failure mode of some bellows seals is the bellows being ruptured leading to premature failure. There are two common ways in which this rupturing can occur. The torsional drive, which in normal operation goes through the spring, is transmitted through the bellows due to the spring disengaging from one end; or from particulates or sharp objects in the water tearing the bellows. The design of AESSEAL's B09-U bellows seal incorporates a patented drive mechanism which not only means that drive is always transmitted through a metal to metal interface but also that the majority of the bellows is encased in a metal shroud during operation. This ensures that the so rubber is not exposed to particulates or sharp objects. What factors do you need to consider when sealing pumps in the water and wastewater sector? With increasing pressure on water companies to reduce leaks, reliability is vital to reduce both environmental and monetary costs. Also time pressed maintenance personnel want to be able to install component seals quickly and be confident that it will be correct. That is why we have developed upgraded alternative designs that fill a gap between component seals and cartridge seals as they incorporate features that improve seal life and aid installation. This is a major step forward in terms of component seals and brings them closer to that of a cartridge seal, reducing the risk of reliability issues. Furthermore, depending on the application, the face and elastomer materials can be critical to the performance and reliability of the seal. A build-to-order model allows greater flexibility to the customer in the water and wastewater industry, who can be assured the most suitable material combination is available at a competitive price. What product design features can maximise sealing reliability? The B09-U contains a rotary drive through the retainer, ensuring that the drive force is transmitted through the retainer and not the bellows, reducing the risk of bellows failure. Maximized material thickness and specially designed spring ensures that disengagement does not occur and reduces the risk of hang up. There is also a pre-tensioned spring, meaning that the amount the seal has to be compressed before it is at the correct working length is reduced, reducing the stress applied to the bellows in its pre-installed state. An 'armadillo' retainer protects the working length of the bellows, while its rotary face is resiliently mounted to make sure it cannot fall out of the seal on installation. AESSEAL has also redesigned its P0-U range seal to incorporate a number of patented features: a flanged drive ring which ensures that the risk of hang up is reduced; an axially retained drive ring which ensures that it will not separate during installation (a common problem with traditional parallel spring seal designs) and full convolution bellows allowing axial movement of the rotary face. The T0-U range has been redesigned to incorporate a patented O-ring groove back up ring. This means that hard O-rings, such as FEPs or TTV, can be offered without compromising the space in which the O-ring operates. Summary We believe that reliability is key to helping companies in the water and wastewater industry reduce costs and improve service to their customers. In re-engineering our component seal range we have achieved this goal, raising the industry standard and allowing configurable component seals to be built to order. Until now few companies have been prepared to invest this amount of time and resource into developing the next generation of component seals. However, we felt that it was important because we now have the same modular build-to-order business model in our component seal range as our cartridge seals – a major step forward. A bellows seal which has become clogged with particulate from a wastewater application A side view of a PO-U rotary head showing the flanged drive ring and axially retained drive ring

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