July/August 2019

Focus on: Seals, Bearings & Lubrication Process, Controls & Plant July/August 2019 www.pwemag.co.uk Plant & Works Engineering | 31 polyurethane, and an inner ring – the energiser – made from softer rubber. The latter’s function is to push the glide ring outwards against the cylinder’s inner wall. For light duties, a simple O-ring works well. For medium and heavy duties, there is a specially shaped energiser made from nitrile rubber. Side vents in the slide ring’s radial side walls ensure pressure activation of the energiser, in response to changes in the pressure’s direction, for rapid seal repositioning. By adapting in this way, cylinder performance is maximised and the potential for a blow-by is lowered. The vents also reduce the chances of producing a pressure trap when the slide ring seals against the radial walls of the seal gland, addressing yet another cause of diminished cylinder functionality. Burge says prototype seals with these design features were rigorously tested against the market’s existing alternatives. This involved over 200 km of up-and-down movement in a 400 mm test cylinder, under 250 bar of pressure and at a temperature of 80°C. Measurements of friction, leakage, extrusion and surface wear confirmed the superior performance of the new seals. In fact, some of the seals against which they were benchmarked failed during the tests. A new class of seals The outcome of this research and development, explains Burge, has been a new class of hydraulic piston seals with tailor-made materials and designs specifically suited to their role. Within industry, the applications of hydraulic machinery are many and varied, so SKF’s engineers have produced a choice of three X-Ecopur PS ranges. The light-duty LPV range serves static indoor equipment such as production machinery. It will cope with pressures up to 250 bar, speeds up to 0.5 m/s and temperatures between -20 and +100°C. More demanding mobile equipment, as used in materials handling, agriculture and construction, for example, will need the medium-to-heavy MPV or DPV ranges. These extend the operating limits to maximums of 400 bar and 1 m/s, with a -20 to +110°C temperature range. LPV and MPV are sized to fit metric housings while DPV is for inch-sized. Given that piston seals lie at the heart of hydraulic cylinder performance, there will undoubtedly be continued research and development in this area. From SKF’s work it is clear that PTFE can be improved upon in terms of durability and flexibility. As a result, users can look forward to greater safety and more reliable, productive and profitable operations. Tel: 0208 339 7370 Fax: 0208 339 7371 Unit 5 Russell House, Molesey Road Email: sales@blackfast.com Walton-on-Thames, Surrey KT12 3PE www.blackfast.com Visit our New Website www.blackfast.com