June 2021

38 n BRAKES, CLUTCHES AND COUPLINGS June 2021 www.drivesncontrols.com Waterworks coupling is still working after 86 years T he TwyfordWaterworks, built in 1898, is still supplying water to the city of Southampton and surrounding areas. With its original Edwardian-era buildings and most of its original equipment still intact, the historic pumping station was designated a Scheduled Ancient Monument in 1973. Thanks to the efforts of volunteers, the restored site is open to visitors on selected dates. In 1985, the non-profit TwyfordWaterworks Trust was established to run the facility. The site is owned by SouthernWater Services which uses electric submersible pumps to extract 22.7 million litres of water from the boreholes every day. Originally, the site’s positive displacement pumps were powered by large steam engines. These were replaced by three diesel engines driving centrifugal pumps in 1934. Gearboxes between the engines and the pumps increase the speed to optimise the pumps’efficiency. A grid coupling that was installed on one of the diesel engine drivetrains in 1934 is still operating. The coupling connects the three- cylinder diesel engine output shaft to the input shaft of the right-angle speed increaser gearbox. This is connected, via vertical line shafting, to the borehole pump 50m below. The coupling was installed to transmit torque while protecting the engine and gearbox from potential damage due to vibration and torsional shock caused by the long driveshaft. It also compensates for any shaft misalignment that might have been present at set-up or occurred due to displacement or settlement during use. For many years, the coupling has been open, allowing visitors to see its inner workings. But, says Paul Fairbrother of the pump station’s internal combustion team,“we plan to close it up soon in order to preserve its internal components for future generations”. The Bibby Turboflex grid coupling is based on a design originally invented by Dr James Bibby in 1917. The RFK212/BK coupling delivered to the waterworks in 1934 is still a current Bibby catalogue product that is manufactured today. The 12-inch (30.5cm) diameter coupling has a 13.7kNm torque rating and a maximum speed of 2,025 rpm. “It's a testament to the Bibby grid coupling’s design and reliability that it's still in production,”Fairbrother says.“The coupling at the waterworks ran full-time from 1934 to the late 1950s, then was in service intermittently into the late 1970s, when the diesel engines were mothballed. I believe the coupling still has its original springs installed as we have a spare set of unused springs in storage that were probably ordered when the coupling was new, but never needed.” According to Andrew Bargh, a product manager in the Altra Couplings, Clutches and Brakes Group, refinements in design and material specifications since the early days have achieved significant improvements in power/weight ratios.“The tapered grid coupling’s circumferential flexibility is progressive due to the curved profile of the grooves that hold the spring in the resilient coupling design,”he explains. “As the grid coupling transmits torque, the flexing of the tapered grid spring damps vibrations and cushions shock loads,”Bargh adds.“This unique characteristic is due to the torsional flexibility of the coupling being proportionate to the unsupported length of each flexible grid rung. The resultant reduction in peak loading protects and extends the life of the transmission equipment.” n A coupling that was installed in 1934 is still operating at an historic waterworks that serves the Southampton area. A spare set of springs ordered when the coupling was new have never been used. The grid coupling, originally installed in 1934, is still operating as part of a diesel engine drivetrain The waterworks coupling transmits torque while protecting the engine and gearbox from damage, as well as compensating for shaft misalignments