Waterworks saves energy

Results from a continuing study by New York’s Monroe County Water Authority (MCWA) indicate that applying low-friction anti-corrosion coatings can restore pump efficiency to the manufacturer’s new-pump specifications.

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PlantServices.com

Results from a continuing study by New York’s Monroe County Water Authority (MCWA) indicate that applying low-friction anti-corrosion coatings can restore pump efficiency to the manufacturer’s new-pump specifications.

In addition to Monroe County, the Rochester-based MCWA supplies drinking water to customers in portions of four other counties, serving a total of more than half a million people. Demand averages 50 million to 60 million gallons per day.

The authority’s pumps experience internal corrosion and rust build-up (tuberculation) in normal operation. The study revealed that cleaning and coating smaller horizontal split-case pumps yields significant efficiency improvements.

“We just couldn’t believe it,” says Paul Maier, MCWA water system analyst. “The results we got from lining pump casings with ceramic-filled epoxy coatings are encouraging news for water suppliers all across the country. Depending on pump size and usage, even a 2% increase in efficiency can pay back the cost of the coating and the labor to apply it in less than one year. In addition to lowering electric bills or increasing pump performance, these coatings may extend the service life of pumps.

Durability, of course, will be a factor in the long run — some of these coatings will last longer than others.”

MCWA conducted the tests during 2004 and 2005 on five single-stage, double-suction, cast-iron, horizontal split-case pumps of less than 100 hp. Based on the encouraging results, the MCWA and the New York State Energy and Research Development Authority (NYSERDA) are jointly funding a test project to coat additional pumps and collect data during the next three years as part of the state’s efforts to encourage the adoption of emerging or under-utilized energy-reducing products and technologies. MCWA engineers and maintenance technicians are now planning the next phase of the testing, which will monitor the effects of several coatings on the efficiency of larger pumps (1,500 hp to 1,750 hp).

MCWA engineers believe that reducing friction is the key to increasing pump efficiency. Without a good protective coating, over time, rust and corrosion produce a rough surface on the pump’s interior casing so the pump must work harder to overcome efficiency losses.

Some of the pilot study’s most dramatic results came from the MCWA’s Moseley Road booster pump, a 75-hp Goulds Model 3405M with 5-in. suction, 8-in. discharge, and a 13.5-in. impeller. The MCWA maintenance department first dismantled and rebuilt the pump, installing new bearings, sleeves and wear rings. MCWA contracted with a local shop to sandblast the pump casing to achieve a white-metal finish (SSPC-SP5).

Next, two products from Devcon (www.devcon.com), chosen by the MCWA for their surface-friction coefficients, shear strength, cavitation resistance, immersion characteristics and overall corrosion-prevention properties, were applied to the freshly prepared casing. Devcon Ceramic Repair Putty was used to fill voids to a uniform surface profile, then two coats of Devcon Brushable Ceramic, which is certified for potable water applications, were applied.

The ceramic repair putty is a durable alumina-filled epoxy compound that repairs and protects worn metal by filling voids and curing to a hard, durable surface. The brushable ceramic is a precision-repair epoxy coating engineered to form a smooth, long-lasting protective barrier against wear, abrasion, corrosion, cavitation and chemical attack. Easily applied with a roller or short-bristle brush, it seals and protects new surfaces and reconditions old ones, improving the performance and longevity of pump casings, impellers, valves, tanks and other critical equipment. MCWA tested other brands of coatings on four other pumps, but variations in the size and condition of the pumps rule out definitive comparison between coatings with respect to their ability to increase pump performance.

The Moseley Road pump lined with Devcon coatings showed significant efficiency gains (see figure). Its efficiency increased by approximately 18% (from about 64% to 82%) as a result of mechanical refurbishment and the cleaning and coating efforts. Based on prior experience, MCWA estimates that at least half of this total increase in pump efficiency was attributable to the cleaning and coating efforts, while the other half came from mechanical refurbishment.

The flow, head and efficiency of the Devcon-coated pump were all restored to the manufacturer’s new-pump specifications. In other words, after cleaning and coating, the pump was as good hydraulically as when it was new. When the MCWA tested the pump’s efficiency approximately six months after commissioning, it showed no measurable decline.

For two of the five pumps in the pilot study, the MCWA crew replaced the bearings, sleeves and wear rings, but reassembled the pump without removing the interior rust buildup. Before sandblasting and coating, the crew then monitored the pump performance (suction, discharge, flow and power consumption) to compare energy efficiency with pre-rebuild readings and to establish a post-rebuilding/pre-coating baseline. This is the only way to quantify how much of a pump’s total performance improvement is from rebuilding and how much is from coating. After several weeks, the pumps were again disassembled, this time for sandblasting and coating. While this type of baseline wasn’t established for the Moseley Road pump and two others, one of the two pumps for which this baseline was established (Woodcliff Station) showed an overall 25% efficiency increase (11% from rebuilding and 14% from sandblasting and coating).