Pumps & Systems, April 2013
While conceptually simple in design, reliable pump operation requires a focus on precision maintenance. However, even simple tasks—such as inspections, level checks and oil changes—can have a profound effect on pump life.
Precision lubrication for pumps requires that the correct lubricant be installed in the right volume and maintained in suitable condition. Lubrication precision maintenance (PM) programs for these systems should be designed around these requirements, but sometimes execution can be difficult unless these items were considered during the design process.
Important accessories are commonly excluded from equipment designs to reduce costs, but the negative effects on maintenance costs and equipment reliability can be drastic. Fortunately, this negligence can be corrected with simple equipment modification in the field.
Pump modifications for precision lubrication can be divided into three categories:
- Contamination control
- Condition monitoring
Most oil-lubricated pump bearings use a bath/splash lubricant application method that presents challenges for precision lubrication. One challenge is that bath lubricated bearings are sensitive to proper oil level, which is half-way up the bearing element, directly in the center. The difference between perfect lubrication and drastic under-lubrication is typically less than an inch of variance in oil level. High oil levels can also cause problems in the form of aeration, excess heat and increased energy consumption.
Many pumps are installed with no effective way to visually inspect the oil level. Instead, they rely on a level plug that requires a technician to remove the plug and insert a probe or add oil until it pours out. This practice can lead to gross contamination of the lubricant. It can also be cumbersome, time consuming and potentially unsafe. In many cases, the oil level does not get checked at all, leading to pump failures caused by undetected, low oil levels.
A good lubrication PM program requires frequent oil level checks and other visual inspections to verify a proper level. To efficiently execute these tasks, all oil-lubricated sumps should be fitted with a visual level inspection device such as a column-type level gauge or a bull’s eye sight glass. These devices should also be properly marked with both high and low levels and possibly running/idle levels. If a column type sight glass is used, good practice is to connect the sight glass vent to the case vent to avoid erroneous readings.
A constant level oiler is also a good option. When properly installed and maintained, the oiler will add make-up oil as needed and maintain the proper oil level at all times. The inclusion of a constant level oiler does not affect the need for a level indicator, which is still required to ensure proper function of the oiler.
The difference between perfect lubrication and drastic under-lubrication is typically less than an inch of variance in oil level. A constant level oiler, similar to the one shown here, is a good option.
Oil is added directly through a filtration unit, further cleaning it and preventing atmospheric contamination by keeping the reservoir sealed.
Another common problem with oil lubricated pumps is getting the oil into the reservoir without contamination. Typical fill ports are small and often require the use of a funnel, which can lead to gross particle contamination of the oil. Proper application methods combined with the appropriate fittings easily eliminates this problem and increases efficiency and safety. By removing fill and drain plugs, replacing them with quick connect fittings and using high quality fluid transfer equipment, oil can be pumped and filtered directly to the sump without exposing it to atmospheric contaminants.
The single largest factor that determines the service life of oil-lubricated bearings is the level of lubricant contamination, whether water, particles or both. The main goal of any precision lubrication program should be the aggressive pursuit of oil cleanliness.
Two primary strategies are possible for controlling contamination in lubricated systems. The easiest and most cost effective is contamination exclusion. The other is contamination removal.
For most oil-lubricated pumps, exclusion is the only reasonable option since they typically do not employ circulating pumps, and offline filtration equipment is usually too large to use with these systems while they are operating. Therefore, contamination exclusion methods should be carefully considered. Most contamination comes from two, easy-to-control sources: new oil additions and the air the sump breathes.
To prevent new oil contamination, it should be filtered prior to use using quick connects with hand pumps or portable filtration units. The breathing issue is easier to address when the problem is understood. Many maintenance professionals may not stop to consider that wet sump applications, such as pumps, breathe significant amounts of air as the temperature in the head space changes. They should remember that this air contains millions of damaging particles that are much smaller than what can be seen with the naked eye. Much of the moisture ingression suffered by pumps actually enters as humidity, which can precipitate when the temperature drops.