Long-term, trouble-free lime slurry pumping

Lime slurry, widely used in water treatment, is a problem for most pump designs due to a tendency to settle out rapidly once pumping stops. This is not the case however for six Watson-Marlow Bredel hose pumps on lime slurry dosing duties at Dwr Cymru Welsh Water's Cefni Water Treatment Works.

The six pumps operate in pairs as duty and standby. Two SP40 (40mm bore hose) pumps were installed in 1993 to transfer freshly mixed slurry to dosing tanks. Maximum speed is 54 rev/min with inverter control turn down to provide flow rates from 430 to 4300 l/h.

Additional pumps were installed when the works was enlarged in 1994. An SP15 pump (with standby) doses 5% lime slurry into the water as part of the treatment process. Using inverters, flow is varied from 25 to 250 l/h based on a maximum speed of 49 rev/min.

An SP25 pump (with standby) handles a 2.5% lime mix on the same duty. Flow range is 82 to 825 l/h based on a maximum speed of 46 rev/min. All pumps operate with flooded suctions and discharge pressures up to 5 bar. Discharge lines vary in length with a maximum of approximately 200 metres.