United Utilities upgrades peristaltics

 
London - United Utilities is to install four peristaltic dosing pumps at its Haslingden Grane Water Treatment Works under a framework agreement with Watson-Marlow Bredel. The 520 series pumps will replace earlier 500 series units which have been in operation at the Rossendale, Lancashire site since 1993.

The framework deal, which has been in place since April 2007, covers the use of peristaltic pumps for the dosing, transfer and metering of liquids and slurries within the water industry. This includes abrasive materials and chemicals such as lime slurry, ferric and sodium hypochlorite, as well as sewage sludge.

At Haslingden Grane, which serves a population of 50,000 people, the 520 series pumps are used for the dosing of sodium hypochlorite - a highly corrosive chemical, which is used in the purification of wastewater and the disinfection of drinking water.

As well as being toxic, sodium hypochlorite emits chlorine in contact with acids and releases tiny bubbles of gas that can collect and cause gas locks in the small ball valves of conventional diaphragm dosing pumps. Peristaltic pumps, however, avoid such problems as they retain the fluid completely within the tube and have no valves that can leak or corrode. 

United Utilities also use the peristaltic pumps for dosing sodium bisulphite – which is used to de-chlorinate the water after disinfection. This is dosed in very small quantities, which requires a high degree of precision and accuracy from the pump. The 520 series pumps can be calibrated either by weight or volume, allowing very precise dosing and metering and allow the user to dose small amounts even at low pressure, without the need for dilution, according to the pump maker.

Generating a flow rate of between 4µl and 3.5 litre/min, the 520 pumps are rated to IP66 for washdown protection. The 520 series delivers user feedback via the pump's own display and have dual analogue input to control and scale speed. They also offer a ‘”drop-in” alternative for diaphragm or piston pumps with variable stroke control, added Watson-Marlow Bredel.