Originally the plant, near Falmouth in Cornwall, employed two conventional diaphragm pumps, however, suffering from blocking due to crystallisation, it was decided to investigate alternatives for the critical process of coagulant dosing. Following discussion with Watson-Marlow, South West Water took two 520DuN/R2 peristaltic pumps on a trial basis. As peristaltic pumps have no valves, seals or glands, and the fluid only contacts the bore of the hose or tube, there is no risk of the pump contaminating the fluid or the fluid contaminating the pump. 

“It was a brave trial from the point of view that we had not used large peristaltic technology for coagulant dosing before,” explains water treatment supervisor, Michael Galligan. “The only peristaltic pumps we had experienced were used for buffer applications on chlorine analysers. Clarification of raw reservoir water is obviously a highly critical part of the process, but we hoped peristaltic would be the answer.”

Sure enough the trial pumps performed without problem over the trial period and a 520DuN/R2 was subsequently purchased and installed into the treatment hall near Falmouth, one of 30 plants in the southwest region. As the process criticality is high, South West Water has a policy of acquiring a back up, hence two pumps were purchased, one for duty and one for standby. Each day South West Water supplies more than 100 million gallons of water to approximately 1.5 million residents, so there is no margin for error or failure.

Within the treatment hall, raw reservoir water is processed through dual stream dissolved air flotation tanks and coagulant (polyaluminium chloride solution) is applied at the front end. The coagulant is applied by utilising a Watson-Marlow 520DuN peristaltic pump, which doses coagulant  between 100-1500ml/min through half inch clear braided hose into the first stage of the purification process via a flow meter.

The pump doses at variable rates that are driven by the raw water conditions and the process is monitored continuously so that the optimum amount of coagulant is applied. For instance, in springtime, algae levels in the raw reservoir water are higher due to increasing sunlight levels and the coagulant requires adjusting accordingly, which is where the variable dosing capability of the 520DuN is invaluable.

Generating a flow rate of between 4µl and 3.5 litre/min, the new 520DuN pumps have a set speed accuracy of 0.1% and can be calibrated by weight or volume for accurate metering. The pumps provide user feedback via a display and have dual analogue input to control and scale speed. For the first time, the 520 series provides industry with a ‘drop-in’ alternative for diaphragm or piston pumps with variable stroke control.

“Since installation the pump has proved faultless,” concludes Galligan. “In fact as a result of this project, our in-house technical standards officer, who is responsible for reviewing technology suitable for company use, has now added peristaltic pumps to the list. The pump is a good, solid product and we are very pleased with its performance.”

Siltbuster, ’s leading designer and manufacturer of mobile silt management equipment, uses peristaltic technology to help remove suspended solids/oil from water pumped from excavations on construction sites. To ensure particles settle more quickly, chemicals are added to the process. The company had relied on diaphragm pumps for chemical addition but grit blocking the valves was a continual problem and meant long periods of downtime were experienced. They now use Watson-Marlow Bredel 500 and 600 series pumps for dosing the flocculant chemicals. The pumps which often run 24/7 are ideal for slurries, viscous, shear-sensitive and aggressive fluids, and are easy to install, simple to operate and inexpensive to maintain.

Another user of peristaltic technology is United Utilities Haslingden Grane Water Treatment Works in Lancashire, . There Watson-Marlow Bredel 520 series pumps are used for two key water treatment functions: the dosing of sodium hypochlorite, a highly corrosive chemical that has disinfection and bleaching properties, and the dosing of sodium bisulphite, used to de-chlorinate water after disinfection. Sodium hypochlorite is a highly corrosive chemical that has disinfection and bleaching properties. It is used in the purification of wastewater and the disinfection of drinking water.  However, dealing with the chemical can be difficult as it is toxic and emits chlorine when in contact with acids.  It 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.

The pumps are also used for dosing sodium bisulphite – which is used to de-chlorinate the water after disinfection and control the level chlorination at that point.  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. This can add an extra degree of complexity to the process. However, this is not an issue for process engineers at the Haslingden site because Watson-Marlow’s 520 peristaltic pumps can be calibrated either by weight or volume, allowing very precise dosing and metering.  This allows the user to dose small amounts reliably even at low pressure, without the need for dilution. 

Generating a flow rate of between 4µl and 3.5 litre/min, the 520 pumps ensure unrivalled levels of accuracy, reliability and control in even the harshest operating environments. Each one is rated to IP66, providing washdown protection for arduous conditions. The 520 series delivers user feedback via the pump's own display and have dual analogue input to control and scale speed. The 520 series provides users with a ‘”drop-in” alternative for diaphragm or piston pumps with variable stroke control.

Because peristaltic pumps retain the fluid completely within the tube and have no valves that can leak or corrode, they can be used for accurate chemical dosing without the need for additional pipework and ancillaries. This avoids complication and considerable cost on-site. 

For both Siltbusters and Haslingden Grane, Watson Marlow Bredel’s pumps offer unrivalled levels of accuracy, reliability and control even in the harshest operating environments. The need for robustness, ease of operation and maintenance, as well as low whole life cost, means that peristaltic technology is winning business chemical dosing applications