Serving the Municipal Water/Wastewater Industry Polymer Coating of Pumps Boosts Efficiency, Performance By William Xia In a typical surface water treatment Discrete water molecules in the flow and distribution system, approximately behave as separate entities creating vor- 70 to 90 percent of the energy used is for tices and cross-currents which result in pumping. With the rising cost of electric- energy losses in addition to those aris- ity, more municipalities are searching for ing from skin friction, which still con- technologies to improve operational effi- tinues to be exerted next to the bound- ciency. One method for improving the ary layer, in a thin film known as the efficiency of pumps is to line the pumps laminar sub-layer. On relatively smooth with a polymeric coating system. surfaces, the thickness of this layer can Polymeric systems have been shown be sufficient to cover surface projec- When applied to fluid flow equip- to provide increased flow at the desired tions, and the surface is said to be ment, this type of coating has been pressure, increased pressure at the hydraulically smooth. proven to improve hydrodynamic per- designed flow, increased efficiency over Where the surface is rough, however, formance by increasing overall efficiency a wide range of flow rates and reduced the sub-layer can be so broken up by through reducing power consumption, power consumption. In many cases, projections that they act as bluff obsta- increasing fluid flow rates or pressure. new water pumps can also benefit from cles, giving rise to form drag. Surface Some polymeric coatings have been an efficiency coating for performance roughness, therefore, either by the effect deemed safe for potable water contact. and protective purposes, even though it has on skin friction or form drag, is This type of coating possesses world- pumps are normally not expected to the most important factor in accounting wide approvals for drinking water con- outperform the original efficiency status for energy losses in a pump. tact, including those from NSF, AWWA, certified by pump OEMs. Even polished metal pump surfaces and authorities in European countries. During the lifetime of a centrifugal are found to be relatively rough when Today’s polymers can produce com- pump, the cost of the energy it con- examined under high magnification. positions which can tackle virtually any sumes is far in excess of the capital cost Further surface roughening can result pump problem. Besides the repair and of the equipment itself. Therefore, effi- from erosion-corrosion or cavitation protection from the damaging effects cient operation of the pump is essential effects, thus causing a reduction in effi- caused by abrasion, cavitation, corro- to optimize operational costs since any ciency of the system. sion and chemical attack, hydraulic effi- increase in fluid efficiency gives imme- Polymer efficiency enhancement ciency improvement by reducing fric- diate savings in power consumption. coatings are specifically designed as tional energy losses has become a more According to case studies, the typical hydrophobic, slick surface coatings and more acknowledged purpose of payback period for a polymeric coating, with low surface energy and abrasion using polymers in pumps. based on reduced power consumption, resistant fillers. They produce an ultra can range from a few months to two smooth surface that reduces the bound- Selection, Application and Operation years depending on the size of pump. ary layer of the pumped fluid and Due to large number of protective reduces internal turbulence, thus polymers and epoxy-based coatings in How Polymeric Coatings Work increasing hydraulic efficiency. the market, selecting the right polymer Most of the energy used in moving The smoothness on the surface of coating for pump efficiency improvement water is actually expended in battling this type of coating is 20 times greater can be confusing. However, there are frictional drag in the water lines. Water than polished stainless steel. The coat- only a few polymer coatings particularly flow in a pump is subject to resistance ing’s hydrophobic nature makes the engineered for pump efficiency improve- caused by volute and impeller surface water simply roll off the surface and ment and effective in new pumps. Using friction and viscosity. wear by abrasion is minimized by its coating products specifically for efficien- In fluid dynamics, water molecules encapsulated blend of lubricating cy improvement and energy savings can on the pump surfaces are stationary. agents and abrasion resistant fillers. attain the ultimate performance poten- Reprinted with revisions to format, from the January 2002 edition of WATERWORLD Copyright 2002 by PennWell Corporation tial, while common protective polymer on energy, flow rate increase and the Trials on New Omega-Pump by KSB, 1999 and epoxy coatings can always help old cost of the coating installation. Trials were performed by applying an pumps improve performance. efficiency improvement coating to four Case Studies new Omega pumps in sizes 250-480 hp. Polymer coating technology is not Afterward, an improvement in efficiency strange to the water industry. Many from 84 percent to 86.9 — 87.5 percent local municipalities, water consumers was measured. KSB acknowledged that and equipment manufacturers have the polymeric coating provided a 2.9 independently tested the effectiveness of percent — 3.5 percent increase in effi- efficiency coatings. Following are some ciency in these four brand new pumps. examples: Sulzer standardized on the use of poly- mer coatings after extensive performance Fayetteville, NC, 1996 testing. Coatings have been applied to After 20 years of service, a high-pres- numerous new pumps, resulting in per- sure pump at the Hoffer Water Plant formance gains. In one case, three iden- revealed 14 percent efficiency loss com- tical pumps were coated with an efficien- Polymeric coatings can be brush or pared to the original test and factory cy coating before being shipped to cus- spray applied in-situ to give a perfectly curve. An unusual noise had developed tomers. The three new split casing pumps smooth high gloss finish. Coatings can be as well. The reconditioning of the pump were tested, and all had achieved a 3.5 cured at ambient temperatures, and post included replacing wear rings, repairing percent increase in efficiency. cured to allow minimal downtime and minor impeller damage, and lining the fast return to service. Being able to carry entire interior surface of the pump with Testing on New ITT A-C Pump, 1996 out polymer coating in-house has led to an efficiency improvement coating. The casing of one new 24 X 16 faster contract turnaround, more compet- The result after reconditioning was WSID centrifugal pump was lined with itive pricing, and better quality control. significant: pump efficiency is up 17 two layers of a polymer coating, and In a typical application, two coats of percent. After reviewing all the data, the the impeller blades were cleaned and different colors are applied by brush, local authority believed that the use of polished. The OEM performance test applicator or spray at a typical thick- the polymer coating was responsible for exhibited a 3.1 percent gain at duty effi- ness of 10 mil per coat. The self-leveling at least 5 percent to 8 percent of the ciency and 3.3 percent at the best effi- features of the coating product ensure a increase. In this application, a 1 percent ciency point. The contributions from smooth surface finish. This finish and increase in actual pump efficiency trans- each individual procedure to the total the coating thickness are critical factors lated to nearly $1,000 per year in elec- success were uncertain. However, the behind the performance without chang- trical savings. The cost of coating the gain from the efficiency coating was ing the water flow characteristics of the pump was less than $2,500. estimated to be at least 1.5 percent. equipment. Two other new units handled with To ensure adhesion, surface prepara- TVA Colbert Steam Plant, Alabama exactly the same procedure passed the tion on the substrate is always required Before 1995, four 60 inch vertical performance test with the same results. by grit blasting, rotary filing, etc. In circulating water pumps were coated \WW/ cases where the pump’s location is sus- with a polymeric coating to protect ceptible to dust contamination, sponge against erosion/corrosion and improve About the Author: William Xia is a chief engineer of blasting offers a good option with a their efficiency. As soon as all wetted water and wastewater industry for Belzona Inc., minimal amount of dust generation. surfaces of the pumps — diffusers, Miami, FL. He is responsible for applying polymeric In pumps that have previously been in deflectors, impellers, casings, etc. were maintenance solutions to mechanical equipment and service, any severely worn or pitted areas coated — remarkable improvements in structures in the industry. Pump renovation and pump can be brought back to the original con- efficiency were observed. efficiency improvement are his major specialties. tours by using a paste grade repair poly- For example, in pump 5a, there was mer compound before coating. a 12 percent decrease in electrical usage In order to document the effectiveness from 100 amps (before) to 88 amps of the polymer efficiency coating in the (after). The motor has been operating at real world, municipalities and water 4160 volts. Assuming the resale of plants can use the coating on certain saved electricity at 4.4 cents / kWh, the water pumps — either old or new — to total electrical savings were $28,411 help assess the technology for a broader within a year. practice. This increase in efficiency does not Operators should document ratings take into effect the increase in capacity with an electricity current gauge or provided by the polymeric coating.