Watson-Marlow Bredel has supplied four of their 520 series dosing pumps to United Utilities for installation at Haslingden Grane Water Treatment Works in Rossendale, Lancashire.
The new peristaltic pumps will replace the earlier 500 series pumps from Watson-Marlow that have delivered trouble-free service since commissioning in 1993.
The new 520 series pumps have been supplied under the United Utilities framework agreement with the Falmouth-based Watson-Marlow Bredel, leaders in peristaltic pump technology.
The framework agreement, in place since April 2007 relates to the use of peristaltic pumps for the dosing, transfer and metering of liquids and slurries within the water industry.
Peristaltic pumps from Watson-Marlow are being used to pump abrasive materials and chemicals such as lime slurry, ferric and sodium hypochlorite, as well as sewage sludge.
According to John Hamer, Process Controller at Haslingden Grane WTW, they first installed the 504 pumps from Watson-Marlow at the plant in 1993 when the site was built, and which have been in continuous use ever since.
The existing 504 peristaltic pumps have always delivered robust performance with very little maintenance requirements.
Reliable, accurate dosing is crucial for the efficient operation of the plant, which the Watson-Marlow pumps have been able to provide since installation.
Mr Hamer says that they decided to continue with Watson-Marlow technology when it was time to upgrade the pumps.
Engineers at Haslingden Grane, which serves a population of 50,000 people, use the new 520 series peristaltic pumps for two key water treatment functions involving the dosing of sodium hypochlorite and sodium bisulphite.
Sodium hypochlorite is a highly corrosive chemical that has disinfection and bleaching properties, and is used in the purification of wastewater as well as disinfection of drinking water.
Dealing with the chemical can be difficult as it is toxic and emits chlorine when in contact with acids. It also naturally releases tiny bubbles of gas, which have a tendency to collect on the small ball valves found in conventional diaphragm dosing pumps.
This can cause gas locks in the system, which prevent the pumps from functioning properly.
Peristaltic pumps retain the fluid completely within the tube and have no valves to leak or corrode, allowing their use in the accurate metering of substances as challenging as sodium hypochlorite without the associated gas locking and maintenance problems.
Peristaltic technology therefore helps to keep costly downtime at the site to a minimum.
The pumps are also used for dosing sodium bisulphite, used in the de-chlorination of water after disinfection.
The chemical is dosed in very small quantities, which requires a high degree of precision and accuracy from the pump.
Often, it is necessary to dilute sodium bisulphite in order to control the dosage procedure accurately, adding an extra degree of complexity to the process.
This is not an issue for process engineers at the Haslingden site because the Watson-Marlow 520 peristaltic pumps can be calibrated either by weight or volume, allowing very precise dosing and metering even at low pressure without dilution.
The 520 series pump is a drop-in alternative for diaphragm or piston pumps with variable stroke control.
Key features of Watson-Marlow 520 series peristaltic pumps:
- Generates a flow rate of between 4ul and 3.5 litres/minute
- High levels of accuracy, reliability and control in harsh operating environments
- Rated to IP66, providing wash-down protection for rigorous conditions
- Delivers user feedback via in-built display
- Dual analogue input to control and scale speed
- Low maintenance requirements