Articles & Case Studies

Watson-Marlow peristaltic pump shifts thinking at Severn Trent

Posted: Thursday 14th June 2012

A 520 DuN/REM high pressure peristaltic pump from Watson-Marlow Pumps Group has met the immediate needs of three chemical dosing schemes implemented recently at various Severn Trent Water facilities. Deployed as part of a temporary dosing rig constructed by engineering group, Costain, the pump’s success is helping to pave the way for future consideration of peristaltic technology. Severn Trent’s historical preference has been to use conventional metering pumps.

“Until recently, Severn Trent Water consistently used a specialist manufacturer of chemical dosing systems, all of which featured metering pumps,” confirms Paul Pearson, Process Commissioning Engineer at Costain. “However, in the past few months, aware that there may be even greater savings available, this arrangement has been relaxed and it’s given us the opportunity to run trials at Severn Trent using a peristaltic pump.”

Triple success

Configured by Costain as part of a portable, temporary dosing rig, the peristaltic-based system has already proved successful on three Severn Trent Water schemes. According to Mr Pearson, there are at least a further half-dozen such applications planned for the coming 12 months, all of which will also use peristaltic technology supplied by Watson-Marlow, although some are larger schemes which might demand a higher flow rate specification than the existing 520 DuN/REM model (108 litres/hour at 4.1 bar).

The three schemes to date have seen the peristaltic pump used for ferrous chloride and ferric sulphate dosing. These coagulants bind with phosphates in wastewater so they can be removed as sludge. The Urban Wastewater Treatment Directive has meant that water companies have to be very stringent about the level of substances such as phosphates that are recorded in treated water, hence accurate dosing is of paramount importance. The pump has also been used to dose with lime for pH correction.

“In my mind there are so many things that can go wrong with a metering pump,” says Mr Pearson, “but with peristaltic, the potential for failure is reduced massively because there are no valves, stators, diaphragms, seals or glands. It makes maintenance extremely straightforward. Only the tubing requires replacement, which is quick and inexpensive, and provided this is done at the recommended intervals, there won’t be any problems. We’ve certainly had no issues so far.”

Increasingly popular

The Watson-Marlow 520REM pumphead features large swept volume with sprung rollers for high accuracy, while the NEMA 4X enclosure delivers wash-down protection for use in arduous conditions such as the wastewater industry. Peristaltic pumps have become particularly popular because nothing but the hose or tube touches the fluid, eliminating the risk of the pump contaminating the fluid, or the fluid contaminating the pump. The pump action is created by compressing the tube between rotating rollers and a track. In between each roller pass, the tube recovers to create a vacuum and draws in fluid. Complete closure of the tube provides the pump with its action, preventing backflow and siphoning, and eliminating the need for check-valves when the pump is not running.




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