A water treatment works in the North West of England was seeking to increase the reliability of their dosing process of treating drinking water. The existing process employed progressing cavity pumps to dose 2% lime solution. The process experienced difficulties caused by wear of the rotor and stator assembly which increases the tolerances in cavity seals required to move the fluid through the pump.
The impact of wear can prove costly for the user
- The pump continues to operate as before but with a reduced performance with the speed to be increased to maintain the flow required, which increases use of energy and increases the rate of wear
- The dosing process itself is compromised with the accuracy of chemical delivery.
- An increase in spares costs with a new rotor and stator assembly. A new mechanical seal and peripheral service items may also be required. This will also require more labour time is required to diagnose which part of the system is at fault and then the time cost in servicing the pump.
A Verder Sales Engineer visited the site to discuss with the Engineering Manager to discuss the site’s process, requirements for compliance and what units can be installed on site.
A Verderflex Dura 55 peristaltic hose pump was selected for 3 reasons
- It is ideal for lime
- It is easy to service
- Offers a great value cost of ownership
The main goals were to increase the reliability and performance of the dosing system and reduce the ongoing maintenance schedule for the existing progressing cavity pumps.
The client was extremely happy with the move to peristaltic technology as the design and performance allows them to identify potential dosing blockages by the reduction in throughput and speed changes. There has only been one hose and lubricant change for the pump since its installation in 2015.
The customer feedback included the fact that there was a cleaner work area from fewer leaking incidents and the pump servicing procedure was far easier with a simple hose and lubricant bath change. The customer was so pleased with the improved performance that the progressing cavity pumps are being phased out and replaced with 7 Dura 55 pumps between now and 2020.
Why did these peristaltic pumps perform so well in this application?
Every pump technology has a ‘sweet spot’ application and for a peristaltic hose pump, dosing liquid lime suspension is firmly there.
- Liquid lime does not cause abrasive wear to peristaltic pumps. The hose the liquid is channelled through is simply compressed and released by a rotor, creating a powerful pumping action. This removes any requirements for moving parts in the fluid stream like a progressing cavity or centrifugal pump. The act of compression and relaxation of the hose also prevents any coating of lime forming inside the pump, eventually causing blockages and accelerated wear.
- The pump provides a constant flow. The pump’s flow rate is directly proportionate to its speed, making it ideal for dosing applications. As the pump has an open channel with a range of hose diameters, even higher viscosity levels of concentrated lime is easily handled.
- As there are no moving parts requiring lubrication from the fluid, the pump can run dry and with the powerful suction properties of the hose and rotor, the pump can self-prime. The direction of the pump can be reversed in the event of an unforeseen blockage.
- Maintenance is simple – Periodically, a new hose and bath of lubricant are required. This can be done in 1-2 hours depending on the size of the pump. In the event of a hose failure, the pumping media is contained within the case, removing the risk to employees and surrounding equipment.