Boost the efficiency of your pump by 30%
The following are excerpts selected from an article in Water World Publication. To view the complete article go to www.waterworld.com
During the lifetime of a centrifugal pump, the cost of the energy it consumes is far in excess of the capital cost of the equipment itself. Therefore, efficient operation of the pump is essential to optimize operational costs since any increase in fluid efficiency gives immediate savings in power consumption. According to case studies, the typical payback period for a polymeric coating, based on reduced power consumption, can range from a few months to two years depending on the size of pump.
How Polymeric Coatings Work
Most of the energy used in moving water is actually expended in battling frictional drag in the water lines. Water flow in a pump is subject to resistance caused by volute and impeller surface friction and viscosity.
In fluid dynamics, water molecules on the pump surfaces are stationary. Discrete water molecules in the flow behave as separate entities creating vortices and cross-currents which result in energy losses in addition to those arising from skin friction, which still continues to be exerted next to the boundary layer, in a thin film known as the laminar sub-layer. On relatively smooth surfaces, the thickness of this layer can be sufficient to cover surface projections, and the surface is said to be hydraulically smooth.
Where the surface is rough, however, the sub-layer can be so broken up by projections that they act as bluff obstacles, giving rise to form drag. Surface roughness, therefore, either by the effect it has on skin friction or form drag, is the most important factor in accounting for energy losses in a pump.
Even polished metal pump surfaces are found to be relatively rough when examined under high magnification. Further surface roughening can result from erosion-corrosion or cavitation effects, thus causing a reduction in efficiency of the system.
Polymer efficiency enhancement coatings are specifically designed as hydrophobic, slick surface coatings with low surface energy and abrasion resistant fillers. They produce an ultra smooth surface that reduces the boundary layer of the pumped fluid and reduces internal turbulence, thus increasing hydraulic efficiency.
The smoothness on the surface of this type of coating is 20 times greater than polished stainless steel. The coating’s hydrophobic nature makes the water simply roll off the surface and wear by abrasion is minimized by its encapsulated blend of lubricating agents and abrasion resistant fillers.
When applied to fluid flow equipment, this type of coating has been proven to improve hydrodynamic performance by increasing overall efficiency through reducing power consumption, increasing fluid flow rates or pressure.
Some polymeric coatings have been deemed safe for potable water contact. This type of coating possesses worldwide approvals for drinking water contact, including those from NSF, AWWA, and authorities in European countries.
Today’s polymers can produce compositions which can tackle virtually any pump problem. Besides the repair and protection from the damaging effects caused by abrasion, cavitation, corrosion and chemical attack, hydraulic efficiency improvement by reducing frictional energy losses has become a more and more acknowledged purpose of using polymers in pumps.
Selection, Application and Operation
Due to large number of protective polymers and epoxy-based coatings in the market, selecting the right polymer coating for pump efficiency improvement can be confusing. However, there are only a few polymer coatings particularly engineered for pump efficiency improvement and effective in new pumps. Using coating products specifically for efficiency improvement and energy savings can attain the ultimate performance potential, while common protective polymer and epoxy coatings can always help old pumps improve performance.
Polymeric coatings can be brush or spray applied in-situ to give a perfectly smooth high gloss finish. Coatings can be cured at ambient temperatures, and post cured to allow minimal downtime and fast return to service. Being able to carry out polymer coating in-house has led to faster contract turnaround, more competitive pricing, and better quality control.
In a typical application, two coats of different colors are applied by brush, applicator or spray at a typical thickness of 10 mil per coat. The self-leveling features of the coating product ensure a smooth surface finish. This finish and the coating thickness are critical factors behind the performance without changing the water flow characteristics of the equipment.
To ensure adhesion, surface preparation on the substrate is always required by grit blasting, rotary filing, etc. In cases where the pump’s location is susceptible to dust contamination, sponge blasting offers a good option with a minimal amount of dust generation.
In pumps that have previously been in service, any severely worn or pitted areas can be brought back to the original contours by using a paste grade repair polymer compound before coating.
In order to document the effectiveness of the polymer efficiency coating in the real world, municipalities and water plants can use the coating on certain water pumps – either old or new – to help assess the technology for a broader practice.
Operators should document ratings with an electricity current gauge or hour-run meter, and use precise measuring instruments for flow rate and water head changes, if feasible, before and after applying polymer coatings. The return on investment can be computed from the comparison of the cost savings on energy, flow rate increase and the cost of the coating installation.