Hidrostal and their pumps have played a significant role in the improvements made to the inlet at the Sewage Treatment Works situated in and serving Esher in Surrey.

Hidrostal and their pumps have played a significant role in the improvements made to the inlet at the sewage treatment Works [STW] situated in and serving Esher in Surrey. The Thames Water project to replace the existing pumps and pipework has been a joint venture between Black and Veatch and Costain who have overall responsibility. Hidrostal were awarded the contract to supply replacement pumps, and fifteen Hidrostal pumps were also used during the over-pumping project.

The refurbishment started with a major over pumping project to keep the sewage flowing to the STW; both the Esher and Hersham pumping stations had to be by-passed ensuring no adverse effect on the residents.

This massive over-pumping project was delivered, installed and commissioned in less than three weeks.

It involved the installation of 10 Hidrostal pumps at the Esher pumping station (maximum flows of 900 l/s), 5 Hidrostal submersible pumps at the Hersham pumping station (maximum flow 410 l/s) and over 370m of pipe was installed (70m at 700mm diameter and 300m at 500mm).

The whole installation was controlled by a telemetry system allowing for remote monitoring.

Once the over- pumping solution was in place the two new Hidrostal pumps could be installed.

As the old pumps suffered from blockages, Hidrostal immersible pumps incorporating the Hidrostal Prerostal self-cleaning sump system were selected.

Each pump operates at 990 rpm and will pump at approximately 480 l/sec.

The screw centrifugal impellers offer high pump efficiency and, due to the impeller geometry and the large free passage, have a very low risk of blocking.

The Prerostal system is unique to Hidrostal.

It has been specifically designed to prevent the build up of solid material floating on the surface and forming a floating raft in the pumping chamber which is often the cause for pumps to block.

It is especially effective on wet wells handling unscreened raw sewage and waste water with oils, fats and greases on the surface.

The Prerostal system comes into operation at low sump levels when a high degree of liquid rotation occurs; the specific geometry of the basin and bellmouth ensures all floating material is entrained by the liquid and pumped out of the wet well.

The system automatically directs all materials which tend to settle or float at every pump cycle to the screw centrifugal pump with its proven track record for solids handling and, as a consequence, provides trouble-free pumping.

Commenting on the total project Dean Clayton, Hidrostal Area Sales Engineer, said: ''This has been an impressive project and a credit to all involved.

The superior rag handling ability of Hidrostal pumps combined with our Prerostal self cleaning sump, has played a key part in ensuring a much improved pumping operation.''