While pumps may be the foot soldiers of the process industries, their quiet dedication means they’re often ignored. That’s a risky business strategy for any site: Components break down, pumps run below optimal efficiency levels, and entire processes suffer. Experts at SKF (Gothenburg, Sweden, and Lansdale, PA) highlight several proven strategies to help optimize your plant’s pump-fleet performance.
Select the right bearing.
Bearings in centrifugal pumps support hydraulic loads imposed on the impeller, the mass of the impeller and shaft, and loads due to couplings and drive systems. They also keep the shaft axial and radial deflections within acceptable limits for the impeller and shaft seal. The bearings often will face high axial loads, marginal lubrication, and high operating temperatures and vibration, all while attempting to minimize friction. If uncontrolled, friction can result in power loss, excessive heat generation, increased noise or wear, and early bearing failure. To optimize a pump’s performance, be sure to evaluate the unit’s bearings (types, designs, and arrangements) in the context of their anticipated operating environment. Suitable bearings are available to satisfy even the most difficult centrifugal-pump applications.
Ensure proper lubrication.
Improper lubrication accounts for more than 30% of bearing failures. Good lubricants prevent metal-to-metal contact and undesired friction. The common methods for the effective lubrication of pump bearings include grease, oil bath, oil ring, and oil mist and air-oil. Oil mist generates the least amount of friction (allowing rotational speed to be based on the bearing design instead of lubrication limitations) and creates a positive pressure within the bearing housing (fending off invasive contaminants). Regardless of lubrication method, always specify lubricants according to the demands on vertical shafts and resistance to solids, pressure, temperatures, loads, and chemical attack.
Seal the system.
Bearing seals in centrifugal pumps retain lubricants or liquids, exclude contaminants, separate fluids, and confine pressure. The choice of a seal for centrifugal-pump bearings depends on the unique demands and operating conditions of the application. Keep in mind, though, that the bearing and sealing arrangement represents an integrated system. Dynamic radial seals generally are the best choice for centrifugal pumps. These designs create a barrier between surfaces in relative motion. Seal selection ultimately must be based on a thorough review of application parameters and environmental factors. For example, seals in pumping applications are often exposed to relatively constant pressure differentials. That makes pressure seals, with their pressurized seal cavities, the preferred choice.
Keep in mind that seals usually have a much shorter service life than the components they protect. Don’t fall into the common habit of scheduling seal replacement only at intervals dictated by other components, such as bearings.
Monitor equipment health.
Regular measurement and analysis of key physical parameters, such as vibration and temperature, can detect pump-system problems before they occur. Basic instruments can assess and report on vibration, temperature, and other parameters. More advanced tools include online surveillance systems and software that can deliver real-time data. Many problems will manifest as vibration, which is widely considered the best operating parameter to judge pump-train condition. Vibration can detect problems such as imbalance, misalignment, bearing oil-film instabilities, rolling bearing degradation, mechanical looseness, structural resonance, and a soft foundation.
Don’t overlook the pivotal role operators can play in pump reliability. They can serve as “eyes and ears” in the detection of equipment faults before problems escalate and also perform basic maintenance tasks. MT
SKF is a global supplier of bearings, seals, mechatronics, lubrication systems, and services that include technical support, maintenance-and-reliability services, engineering consulting, and training. For more information on motor bearings and other technologies and topics, visit skf.com.