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Polymer coatings can significantly improve water pump efficiency

coated pump impeller

Fluid handling equipment may suffer from multiple problems, including physical and mechanical damage, as well as general or localized erosion and corrosion. These problems are linked to decreased efficiency and poor performance, leading to increased operational costs.

Minimizing performance deterioration is, therefore, an important factor for pump manufacturers and end users. Indeed, hydraulic losses account for most of the efficiency decrease (from 9% for a mixed flow pump to 20% for radial flow). Coating technology can help in decreasing these losses, increasing pump performance and reducing operational costs.

In pumping equipment, it is possible to reduce power consumption and improve the hydraulic properties by changing the pump surface finish. In fact, the loss of efficiency is caused by frictional forces created between the fluid and the walls, acceleration and slowing down of the fluid, and change in fluid flow direction.

In order to get the best performance and water pump efficiency, manufacturers seek to create the smoothest possible surface. This can be achieved by polishing the selected metal. However, this method is time-consuming and expensive.

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impeller comparison
Pump impeller before (L) and after (R) being repaired and coated.

A smooth surface finish can also be obtained by applying an erosion and corrosion resistant efficiency coating on the pump’s volute and impeller. These polymeric coatings are specifically designed to improve efficiency on fluid handling systems and protect metals against erosion and corrosion.

Properties, such as self-leveling application, hydrophobicity and hydraulic smoothness, make these coatings candidates for lining pumps. These coatings possess a low electronic affinity towards water molecules and result in a smooth glossy finish once applied onto a metallic surface. This allows water, or other aqueous solutions, to easily slide on the surface of the coating.

The smoothness of these hydrophobic epoxy coatings has been measured as fifteen times smoother than polished stainless steel. As a result of the smoother surface and reduction in flow resistance and friction, the hydraulic performance of the pump can be increased.

Testing of a Belzona 1341 coated pump gave a maximum of 6% increase in peak efficiency and a reduction in power consumption of 5.1 kWh at duty point. Assuming a 5,000 hours operating cycle/year, the power savings over this period would amount to 25,500 kWh.

In 2013, a water elevation plant was looking for a solution to improve its hydraulic efficiency. This plant had high energy consumption and costs, with an annual consumption of 1.7 GWh/year and a volume of water propelled of 1.2 Mm3/year recorded in 2012.

The client was looking for a reliable and long-term solution to restore a damaged pump, while reducing internal friction in the impeller and volute to enhance hydraulic efficiency. An internal pump coating was chosen to maximize water flow and reduce energy consumption. The pump was disassembled and all internal surfaces were grit blasted to remove the previous coating, creating a substrate cleanliness of at least SA2,5 and a surface profile of at least 75μ. The surface was then cleaned and examined to ensure that it was free of dust and other particles.

After grit blasting, areas were masked for the application of Belzona 1111 (Super Metal), an epoxy paste grade composite for metal repair. Simply applied using an applicator provided with the product, this material was used to reconstruct areas damaged by corrosion, rebuilding the original surface profile.

Within the two-hour over-coating window, the first coat of Belzona 1341 (Supermetalglide) was applied by brush, followed by a second coat to obtain a total dry film thickness of 500μ. This coating was specified because it provides protection against erosion and long-term corrosion.

performance graph
Performance curve of a new pump before and after coating with Belzona 1341.

After coating the pump and making changes to the programming of the water elevation plan, energy consumption was reduced during non-peak hours from 44.9% to 39.3%, a savings of 12.5%. Four months of savings covered the pump refurbishment cost.

For more information, visit www.belzonagreatlakes.com This article appears in ES&E’s November/December 2015 issue.

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