Hidrostal Solve Pump Blockage Problem


The Netherley Sewage Pumping Station (SPS) is a traditional wet/ dry well located in the United Utilities area on the outskirts of Liverpool. It is a terminal SPS and pumps directly to the inlet at Woolton WWTW approx 1.5 miles away.

The pump houses four pumps which were originally installed in 1968. In 1998 United Utilities decided to replace the pumps as they were beginning to wear out and the company that supplied them was no longer trading. United Utilities purchased four 200mm discharge dry well submersible pumps with 102mm throughlet (impeller free passage). However, only one was ever fitted and put into service as the pump suffered from severe ragging problems despite the supplier trying various impellers over a 4 year period. Barrie Holmes, United Utilities, Field Services Engineer remembers: ‘The pump blocked continuously. The longest it went without blocking was 18 hours and during storm conditions the pump would have to be lifted two or three times a day’.

Subsequently, early in 2004 Hidrostal were contacted and asked to supply a replacement pump. The solution was proposed by Ivan Finch, Hidrostal’s Sales Engineer, who explains: ‘Following extensive analysis of the situation it was clear that the blockage problem was caused by the pump having an enclosed impeller To handle raw sewage it is essential that pumps have a large free passage and an open impeller geometry. I proposed the Hidrostal HO8K-H Screw Centrifugal pump, with a 145mm impeller free passage and running with a VS drive between 1460 and 950 RPM giving a flow of between 200 and 100 lit/sec. In mid June 2004, we removed the problem pump and installed the Hidrostal HO8 with some slight modifications to the pipework. Since installation, to the delight of the site operators and engineers, the pump has not had to be touched and there has been no problem with blockages’

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