Three pumps only one hose replacement in four years

Only one replacement hose in four years is the record of three Watson-Marlow Bredel SP50 hose pumps installed on auto-desludging duties at Dwr Cymru Ruthin Sewage Treatment works.

Ruthin STW, which serves the town's 5,000 population, was upgraded in 1996, when a third primary tank was added, and a computer operated auto-desludging system was introduced in the Works to replace the old system based on the manual opening of valves.

One SP50 pump is installed for each tank, each running once per hour, handling four to six per cent dry solids content primary sludge at a rate of 4900 litres/hour. Pump speed is 28 rev/min; discharge pressure 5 bar. The pumps are fitted with 2.2 kW cast iron frame motors with fixed-speed gearboxes.

The pumps were installed complete with associated pipework and valves and are fitted with automatic cut-out switches to protect against blockage in the suction or discharge lines. Suction and delivery lines are also fitted with surge dampers.

As well as requiring only minimal routine maintenance, the three SP50 pumps have desludged consistently at the specified rate without interruption to flow or "rat holing".