Watson-Marlow peristaltic pumps were chosen by OTV Birwelco for lime slurry dosing duties at West of Scotland Water's new Penwhirn Water Treatment Works, Dumfries and Galloway. Three pairs of variable speed pumps are currently in service operating as duty and standby units and are part of a £16 million contract.
According to Rob Barton, OTVB's Project Manager, "We chose Watson-Marlow pumps because they are simple, reliable, easy to maintain, accurate and have no trouble with the slurry settling out." Diaphragm pumps were also considered for the duty but the tendency to settle out very quickly in low velocity areas is a characteristic of lime slurry and this can result in blockage, component failure and leakage in many pump designs. In the Watson-Marlow design the flow path is "straight through" without valves, vanes, diaphragms or other obstructions where product can settle out and blockages occur.
Mr Barton also cites the level of service as an important factor. "At all stages, before, during and after installation the service and pumping knowledge provided by Watson-Marlow staff was first-class."
Lime slurry is used in water treatment for pH adjustment. The pumps draw from two automatically interchangeable, agitated, slurry mixing tanks and dose directly into the main. Dosage pumps operate from 9 litres/hour to 708 litres/hour, continually adjusted to match flow through the main and the pH level by signals from flow meters and pH monitors to AC frequency inverters.
All six pumps at Penwhirm are fitted with NBR hoses, WIMES specification motors and high lubricant level detectors for hose failure indication.