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Figure 1: Hard case In abrasive service pumps, wear-resistant materials once reserved for rotating parts are now being used for stationary components as well. But most experts identify seals and bearings as the traditional limiting components when it comes to pump life and maintenance, and those areas are where advanced materials are making the most significant improvements. Long live the seals
Process-pump sealing technologies continue to move from wet/contacting to dry-running designs. "Dry-running, non-contacting gas seals, common in compressors and turbines, are becoming more standard in process pump and slower-shaft-speed applications such as mixers," says Mike Kraus, market development manager, John Crane Inc. (www.johncrane.com).In traditional seals, mating faces run against each other, resulting in friction and wear and requiring lubrication. Non-contact seals are designed with an engineered pattern on the face so one surface lifts off from the other. Air or gas forms the seal. Friction and its associated wear and heat are significantly reduced, which extends seal life for longer maintenance intervals.These seals are effective even for highly regulated or hazardous fluids. "We continue to have increasing success using high-pressure gas seals and nitrogen gas to seal hazardous materials," says Tom Bennett, marketing manager, Flowserve (www.flowserve.com). "This approach increases mean time between failure and helps us reach our goal, which is to save customers downtime."For dry-running seals, where faces are in contact and there is no fluid for lubrication, there are new materials and designs that reduce heat and wear. Some offer improved wear resistance for both wet and dry running and for unloading operations, for example, where there may be nobody there to turn off the pump when the freight car or tank is emptied.In one example, the traditional soft face/hard face combination (i.e. carbon graphite/silicon carbide) is being replaced with designs where both faces are made of the same silicon carbon/graphite composite, which combines the lubricity of carbon graphite with the wear resistance of silicon graphite. The result is a seal with improved abrasion resistance and dry-running capabilities.In another application, seals made of a sintered composite of silicon carbide and graphite were able to withstand five hours of dry running on an agricultural chemical pump. "Over 100,000 pairs of seals based on this new material have been supplied for the past two seasons for many tough applications, including trailer-mounted pumps," says Joseph Boylan, vice president, market engineering, Morgan AM&T (www.mamat.com). "And, according to the users, not one seal has yet failed," he adds.More cartridges
Progress is particularly concentrated in seal cartridges. "A seal is only as good as the alignment and installation, and companies these days have lost a lot of the experienced mechanics who can properly install multi-component seals that have to be aligned within thousandths of an inch," Kraus says. "It's become important for us to simplify installation and minimize the chance of error. With a cartridge, you slide it into position, tighten it up, and you're ready to go."Factory-assembled cartridges can be preassembled, pressurized and tested for loss under simulated operating conditions. Seals that are field-assembled from components can't be fully tested until they're installed on the equipment, when any problems can cause an expensive extended shutdown or emergency repair.Preassembly in cartridges eliminates handling damage such as fingerprints and tiny scratches on O-rings and lapped surfaces that can reduce seal life. "Our most advanced technology goes into our cartridge seals," Kraus adds. "They can have higher numbers of more complex parts. To expect the end user to put them together would be inappropriate."Cartridges can last longer due to more precise alignment, proper seal setting and better materials. They can more than recoup their higher initial cost with fewer startup failures and more uniform service lives. "At, on average, $2,000 to $3,000 in maintenance cost per changeout of a seal that costs less than $1,000, it makes sense to use a cartridge that should last 36 months instead of six to 12 months or less for an incorrectly installed, site-assembled seal," Kraus says. Way better bearings
The same corrosion and wear-resistant properties that make carbide-graphite composite seals last longer are improving the performance of sliding-element bearings, giving them critical resistance to abrasive fluids and run-dry conditions (see Figure 2)."Vibration-prone applications, such as pumps with mechanical seals, can benefit from these bearings because their running clearances can be made tighter than those for other bearing materials," says Eben Walker, general manager, Graphite Metallizing (www.graphalloy.com). "The coefficient of expansion of these materials is about half that of steel, so shaft clearances are typically in the range of 0.008 in. to 0.012 in., less than one-third of those required for metallic parts. In fluid-handling systems, this has the added benefit of less leakage and greater efficiency."
Bearing isolators wear longer and do a better job of keeping lubricants in and contaminants out, in some cases halving maintenance and doubling mean time between failures.The company claims the isolators more than double mean time between failure. It says protected bearings have run 50,000 hours (5.7 years) or more, and running the bearings under optimal conditions can let pumps last five to 10 times longer.Data, data, data
There's no way to complete an article on technology trends in industrial equipment, pumps or otherwise, without acknowledging advances in sensor technology, data acquisition and data processing that fuel predictive and reliability-centered maintenance, and pumps are seeing their share.Pump vendors agree that condition monitoring is becoming a must. "Intelligent pumping systems with embedded sensors and controls provide for smoother startups and production changes, tighter control during continuous operation and faster diagnosis of system problems," says Mike Pemberton, manager, business development and marketing, ITT PumpSmart Control Solutions (www.gouldspumps.com). "[This is] before product quality or process operation is negatively affected," he says.Plants are doing more online condition monitoring, often by cooperating or contracting with equipment vendors. "Our condition datapoint monitoring service monitors each covered piece of equipment for vibration, temperature, pressure, flow and other target points," says Flowserve's Bennett. "By following trends and doing predictive maintenance, we can take action before a failure.""High reliability and availability are the primary customer requirements modern pump suppliers are confronted with," says Nils Kohlhase, manager, research and development, Lewa (www.lewa.com). "Monitoring systems can make a decisive contribution."