Figure 3: Suction Inlet of 18x16 400 HP Pump, (Post Sandblasting / Epoxy Ceramic Coating "Courtesy of Monroe County Water Authority, Rochester, NY"Click here to enlarge image5. Methods of reconditioning pumps:
a. Waterways: There are many aftermarket methods for reconditioning pump casings and/or impeller internal passages, including wire brushing, sand/grit blasting and coatings. The Monroe County Water Authority, in collaboration with the New York State Energy and Research Development Authority, is in the middle of a study focusing on measuring the performance and efficiency enhancement from sandblasting and then coating of the casing interior with epoxy ceramic coatings. The study group of centrifugal horizontal split case pumps had been in service for a minimum of 10 years (see figure 3). They are using several different brushable epoxy coatings (Belzona, Chemclad & Henkel Locktite) for this study. They found that in most cases, the interior coatings increased pump efficiency by 5 – 10% or greater, which represented a recovery of about 70% to 80% of the friction loss. With the power consumption of these pumps in the range of 20 to 1750 HP, for this 50 mgd public drinking water supplier, reconditioning these pumps should achieve a sizable energy savings.
b. Wear Ring Clearances: Replacing pump wearing rings is normally a relatively easy fix, which will not only improve the efficiency and head of a pump, but will also reduce the NPSH requirement, since less flow and turbulence will be going through the eye of the impeller. The lower the pump specific speed (the lower the flow and higher the head), the greater will be the impact of wearing ring clearance on pump performance. There are non-galling composite materials, such as DuPont’s Vespel CR-6100, that will allow the wearing ring clearances to be reduced below the manufacture’s specification, saving even more energy and further reducing NPSHR
About the Author:
Allan R. Budris, P.E., is an independent consulting engineer who specializes in training, failure analysis, troubleshooting, reliability, efficiency audits and litigation support on pumps and pumping systems. With offices in Washington, NJ, he can be contacted via e-mail at [email protected].