Combined 50,000 service hours from lime dosing pumps

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A story of unusual service longevity of lime dosing pumps has emerged from South West Water's Restormel Water Treatment Works, located near Lostwithiel in Cornwall. It started in 2001 when the company approached dosing specialist Gee & Company to review a history of lime pump failures at the site.

Amongst the challenges at Restormel was a need for very long lime slurry dosing lines running across the site from a central dosing room location to the required injection points at the outlet of the chlorine contact tank.

For the application, SWW advised that the existing carrier water be utilised, but that its flow-rate would need to increase so as to reduce the 'closed loop' control reaction time. Historically, this was why previous pumps had great difficulty in combating the high delivery pressures that were thus induced.

As a potential solution, Gee & Company proposed the introduction of its Signal 300 series dosing pumps. These hydraulically actuated diaphragm pumps are capable of much higher pressures than are demanded by the application. They are also designed to cope with the known problems of lime dosing and delivering very long diaphragm life.

The pumps were installed on a trial basis in 2002, together with a new backboard containing all necessary pipework, valves and carrier water connection points. Pump duty was established at up to 1,500 litres/hour, working against a back pressure of 8 bar or higher - due to the long dosing lines and the increased carrier water flow-rate.

At Restormel, the installed dosing pumps had to accommodate extreme seasonal variations in dose requirements due to the change in the iron and manganese levels in the raw water.

The changes proved not only to be effective but also easy to implement by SWW staff. It was also noted recently, whilst checking spares inventories, that the pumps had required only routine hydraulic fluid checks during their six year operational period and, to date, had no requirement for any spares.

Operations staff noted that these pumps are still running as smoothly as when they were installed. This was confirmed by photography of the 'hours run' meters, which showed that the combined run duration was almost 50,000 service hours. Since then, this figure has already been exceeded.

This longevity was further facilitated by South West Water implementing their policy of cycling the duty/standby pumps regularly. The operational staff were naturally pleased with these levels of performance and stated that the dosing pumps have proved to be very effective without any failures and with very low maintenance requirements.

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