Balance Your Lube Filtration
EP Editorial Staff | July 1, 2021
The goal is to remove contaminants at the rate they are introduced into lubricants.
By Mark Barnes, PhD, CMRP, Des-Case Corp.
When it comes to lubrication, nothing is more important than fluid contamination control. In most lubricated assets, contamination accounts for as much as 70% to 80% of lubrication-related reliability problems. In hydraulic systems the numbers often approach 90%. Despite this widely held knowledge, many companies struggle to achieve best-in-class contamination control targets for one reason—lack of balance. Balance simply means that the rate that particles, moisture, and other contaminants are removed or eliminated exceeds the rate of contamination ingress.
To understand the concept of balanced filtration, consider the three trend lines shown in Figure 1, which represent the application of portable filtration to control contamination in a gearbox. In the first (gold) trend line, which represents a system without filtration, particle ingression causes the particle count to double each day, rapidly exceeding the 80 particles/ml limit at 14 microns for a gearbox with a target cleanliness level of 18/16/13. The second (red) line shows what happens when a portable filtration system is connected every seven days with a particle-removal effectiveness of 60%. Despite using a filter system to reduce particle concentrations, the relatively high ingression rate, coupled with the relatively poor filtration efficiency, means the total number of particles remains well above the desired target cleanliness level and steadily increases. The first and second lines show systems that are out of balance.
The third (blue) line shows what happens when filtration is handled by a system with a 90% particle-removal efficiency. In this balanced scenario, the rate of particle removal closely matches the ingression rate and cleanliness levels remain below the desired target.
Balanced filtration goes way beyond the capture efficiency of a filter cart. To maintain balance, every aspect of the contamination control policy and strategy needs to be considered and steps taken to minimize contamination ingress while maximizing removal. This process is known as holistic contamination control.
Start with storage & handling
Controlling contamination at its source is a critical first step since the condition of new oils in storage will affect every machine in the plant. With few exceptions, new oils have particle counts ranging from two to three ISO Codes or four to eight times higher than recommended. Since oils are naturally hydroscopic, care should be taken to exclude moisture and, if necessary, filter using water-removal filtration elements.
To achieve balance in the storeroom, focus on three elements:
• Ensure that all containers and transfer vessels remain sealed and that transfers occur through quick connects so the oil is never exposed to the ambient environment.
• Add appropriately sized desiccant breathers to all containers so the air that enters the storage vessel when oil is dispensed is free from particle and moisture contamination.
• Pre-filter new oil with an appropriately rated filtration system a minimum of five to seven times to ensure target cleanliness levels are met.
Critical Control Points
A critical control point (CCP) is anywhere oil is transferred from one container to another or from a container to a machine. These transfers are major sources of contamination ingress. All CCPs should use quick connects to avoid contact with the ambient environment, as well as color and shape tagging to identify the lubricant type to avoid accidental cross contamination.
As stated previously, balanced filtration simply means making sure that the rate at which contaminants are removed is equal to or greater than the rate of ingression. To do this, all critical assets should be configured so that simple tasks such as level checks, oil top-offs, and oil sampling can be conducted without exposing the reservoir or oil sump to the ambient environment. As with storage tanks and containers, all critical assets should include a desiccant breather to prevent contamination ingress due to volumetric oil-level changes or thermal syphoning during normal operation. Controlling the rate of contamination ingress on the front end lowers the cost of the investment in downstream oil filtration.
Properly spec oil filters
While contamination exclusion should always be the initial focus, any balanced contamination-control strategy requires filters that are properly specified based on their beta-capture efficiency and dirt-holding capacity. All filters should have a minimum beta rating of 200 and preferably ≥1,000 at the appropriate micron size. Table 1 illustrates the filter micron size rating required for various levels of fluid cleanliness. Note that several additional factors, including ingression rate, oil flow rates, operation duty cycles, and filtration system design, influence particle-capture efficiency and, hence, the optimum filter rating.
In some instances, it’s not possible to adequately remove contaminants at a sufficient rate with full-flow filtration to maintain balance. This may be due to high ingression rates, limitations on oil-flow restrictions caused by finer filtration, and/or an inability to cost effectively improve full-flow filtration to deliver sufficient particle-capture efficiency. Where full filtration proves ineffective at maintaining balance, offline filtration—permanent or periodic—should be used.
For non-circulating systems without system filters, the only effective means to achieve balance is to add offline filtration. Like circulating systems, this can be either permanent or periodic using filter carts and skids.
The goal of balanced filtration is to ensure that the oil remains at or below the target cleanliness and dryness level for optimum system reliability. How do we know we’re in balance? The answer is oil analysis. Any well-designed, balanced filtration strategy
requires that routine oil sampling be performed to validate that all contamination control devices are creating balance. EP
Mark Barnes, CMRP, is Senior Vice President at Des-Case Corp., Goodlettsville, TN (descase.com). He has 21 years of experience in lubrication management, oil analysis, and contamination control.