Effective pump maintenance allows industrial plants to keep pumps operating well, to detect problems in time to schedule repairs, and to avoid early pump failures. Regular maintenance also reveals deteriorations in efficiency and capacity, which can occur long before a pump fails. Wear ring and rotor erosions, for example, can be costly problems that reduce wire-to-water efficiency by 10 percent or more.
The amount of attention given to maintenance depends on how important a system is to a plant’s operations. Downtime can be expensive when it affects critical processes. Most maintenance activities can be classified as either preventive or predictive. Preventive maintenance addresses routine system needs such as lubrication, periodic adjustments and removal of contaminants. Predictive maintenance focuses on tests and inspection that detect deteriorating conditions.
Preventive Actions
Preventive maintenance activities include coupling alignment, lubrication and seal maintenance and replacement. Mechanical seals must be inspected periodically to ensure that either there is no leakage or that leakage is within specifications. Mechanical seals that leak excessively usually must be replaced.A certain amount of leakage is required to lubricate and cool the packing seals, but the packaging gland must be adjusted if the leakage exceeds the manufacturer’s specifications. The packing gland must be replaced if it has to be tightened excessively to control leakage. Overtightening causes unnecessary wear on the shaft or its wear sleeve and increases electric power use.
Routine maintenance of pump motors such as proper lubrication and cleaning is also vital.
Predictive Actions
Predictive maintenance helps minimize unplanned equipment outages. Sometimes called “condition assessment” or “conditioning monitoring,” it has become easier with modern testing methods and equipment. Several methods apply to pumping systems.Vibration Analysis.Trending vibration amplitude and frequency can detect an impending bearing failure. It also can reveal voltage and mechanical imbalances that could be caused by impeller, erosion or coupling problems. Changes in the amount and resonance of vibration over time are more meaningful than a single “snapshot” of the vibration spectrum.
Motor Current Signature Analysis.Sometimes called “dynamic analysis,” motor current signature analysis can reveal problems such as deteriorating insulation, rotor bar damage, electrical system unbalance and harmonics. It also can pick up system problems such as malfunctioning control valves that cause flow rate disturbances. Again, tracking the signature over time is more valuable than a single snapshot.
Lubrication Oil Analysis.Though it applies only to large, oil-lubricated pumps, and it is an expensive procedure, oil analysis is an effect predictive maintenance tool. It can detect bearing problems caused by metal particles, chemical changes that result from overheating, and seal problems caused by pumped fluid in the oil. It also provides guidance on proper oil-change intervals.
Periodic Efficiency Testing.Testing the wire-to-water efficiency and keeping records to spot trends is useful.
Maintenance Checklist
As a part of the maintenance plan for any industrial plant that uses pumps, routine checks should include the following action items.Packing.Check for leakage and adjust according to the instructions of the pump and packing manufacturers. Allowable leakage is usually two to 60 drops per minute. If leakage exceeds the recommended rate, add packing rings or, if necessary, replace all the packing.
Mechanical Seals.Check for leakage. If leakage exceeds the manufacturer’s specifications, replace the seal.
Bearings.Determine the condition of the bearing by listening for noises that indicate excessive wear, measuring the bearing’s operating temperature and using a predictive maintenance technique such as vibration analysis or oil analysis. Lubricate bearings according to the pump manufacturer’s instructions, and replace them if necessary.
Motor/Pump Alignment.Determine if motor/pump alignment is within the service limits of the pump.
Motor Condition.Check the integrity of motor winding insulation. These tests usually measure insulation resistance at a certain voltage or the rate at which an applied voltage decays across the insulation. A vibration analysis can also indicate certain conditions within motor windings and lead to early detection of developing problems.
The list of maintenance tasks can be tailored for many kinds of systems, applications and facilities. Many manufacturers can help you optimize your pumping system operation.
This article was provided by the Hydraulic Institute, the U.S. Department of Energy and Pump Systems Matter.
The Hydraulic Institute, Parsippany, N.J., is an association of pump producers in North America that serves member companies and pump users by developing industry standards, providing education and training, and serving as a forum for the exchange of industry information. For more information from the Hydraulic Institute, call (973) 267-9700 or visit www.pumps.org
The DOE’s Industrial Technologies Program, through partnerships with industry, government and nongovernmental organizations, develops and delivers advanced energy efficiency, renewable energy and pollution prevention technologies for industrial applications. For more information from the DOE’s Industrial Technologies Program, call (877) 337-3463 or visit www.eere.energy.gov/industry.
Developed by the Hydraulic Institute, Pump Systems Matter is an educational initiative created to assist North American pump users gain competitive business advantages through strategic, broad-based energy management and pump system performance optimization. For more information about Pump Systems Matter from the Hydraulic Institute, call (973) 267-9700 or visit www.pumps.org.
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