In use on a digester feed duty, two Watson-Marlow Bredel SP50 hose pumps are located at Dwr Cymru, Gresford Sewage Treatment Works.
Installed in 1991, the SP50 pumps operate as duty and standby running at a speed of 28 rev/min and delivering a metered flow of 4900 litres/hour. A pre-determined running time enables a calculated volume of sludge to be fed to the digester over a given period.
The pumps replaced mechanically operated single diaphragm pumps which were proving unreliable and expensive to maintain due to the long suction line, and a discharge rising vertically to the top of the digester. In addition, output tended to fall away when handling thicker sludges.
In the event of duty pump failure at Gresford, the standby hose pump cuts in automatically to ensure interruption free flow to the digester. The pumphead housing is fitted with a high lubricant level sensor, designed to switch the pumps over if a hose replacement becomes necessary.
Due to the long suction line (30 metres), an inlet pulse accumulator is fitted in the discharge pipework to guarantee a smooth flow of sludge to the pump inlet, and a damper is installed in each discharge line to smooth out pulsations in the feed to the digester. The system is further protected by blockage sensors in suction and discharge pipework.
Since the SP50 pumps were introduced, maintenance and downtime has been very low with only an average of one replacement hose per year, so keeping costs to a minimum.