January 2020

33 www.drivesncontrols.com January 2020 A t its Cerney Wick site in Gloucestershire, Hills Quarry Products produces aggregates. The site’s processes demand a high volume of water which returns to a sump for pumping to a settling bed. In the past, float level switches in the sump were used to activate a fixed-speed pump to perform this transfer. However, the fixed-speed operation could be too high for demand, leading to the sump running dry and the pump failing. In addition, because the motor only ran at one speed, the stress on the pump set was leading to problems such as broken transmission belts, motor over-currents and blocked pumps, resulting in costly failures that were happening about once a fortnight. “The pump could be out of action for a few hours to a full day, depending on whether it was a simple belt change or if the pump needed to be raised from the sump,” recalls the quarry’s manager, Olly Thompson. “We extract between 1,000 and 1,200 tonnes of aggregate every day at Cerney Wick, so any downtime is extremely costly – not just in terms of lost production, but also due to the extra expenses incurred by our maintenance team and external contractors.” Following a recommendation from the Bristol-based drives suppler, APDS, a 55kW ABB variable-speed drive and level control device were installed to adjust the pump motor’s speed automatically, according to demand. A pressure transducer, installed in the sump, now monitors the water pressure. The VSD then calculates the water level that corresponds to this pressure, and adjusts the pump speed to avoid overflows and to prevent the sump from running dry. “This system has reduced downtime, increased production and reduced the number of replacement drive belts as well as the cost of repairing the pump when it ran dry,”Thompson reports.“As well as avoiding failures and the associated costs, we have also cut electricity usage on the application by around 50% by matching the motor speed to demand, achieving further savings.” n VARIABLE-SPEED DRIVES n The quarry’s sump pump was experiencing frequent failures before a VSD was installed to control it. Quarry ends frequent pump failures by installing a VSD A critical sump pump at a Gloucestershire quarry was failing about once a fortnight. Installing a VSD to control the pump has reduced the failure rate and cut maintenance and energy costs. Hills Quarry Products can now extract up to 1,200 tonnes of aggregate per day without the risk of pump failures following the conversion of a fixed-speed motor to variable-speed control.