Purpose-manufactured hose reduces running costs

Significant savings in operating costs at North West Water's Belmont STW followed a decision to revert to the use of purpose-manufactured hoses for two Watson-Marlow Bredel SP50 hose pumps on sludge transfer duties.

The pumps at Belmont were installed in 1991 and had an excellent service record, but approximately two years ago, as part of a quest for lower operating costs, it was decided to adopt cheaper, non-standard "pirate" hoses and lubricant from another source. This proved a false economy.

While hose life was shortened by around 50%, time spent on hose changes virtually doubled, due in part to the fact that the "pirate" hoses had to be cut to length each time.

As well as irregularities on the surface of the hose which led to the pump's pressing shoes becoming worn and requiring periodic replacement, variation in the wall thickness imposed an overload on the pumphead bearings. The eventual bearing failure - unobserved for a time on an unmanned site - ended in major damage to rotor shaft, bearings, grease seals and housing. This necessitated supply of a complete new pumphead at a cost of £2,500.

Overloading the bearings also imposed additional wear on gearboxes and increased power consumption.

Finally, due to inconsistencies in bore of the hose, the pumps flow rate was variable due to back streaming. To compensate, the pumps were required to run faster and for longer periods, with an adverse effect on running costs and the overall efficiency of the sludge handling system.

Following consultation with Watson-Marlow Bredel, North West Water have changed back to using true Bredel hoses and lubricant in the SP50 pumps at Belmont and the two pumps are once again giving good service, running over a speed range of 10 - 63 rev/min with output 1,750 - 11,025 litre/hour.