Anyone comparing oil absorbing liquid filter bags will see efficiency numbers that look simple: 95 percent, 98 percent, 99 percent. The number is useful, but it is only as specific as the test behind it. Two bags can carry the same rating and still behave differently in a real process because one sees light oil at low flow and the other sees thick fluid, fine particles, or a heavy contaminant load. Understanding the rating language helps readers separate a manufacturer-stated design range from a guaranteed outcome.
How Filter Efficiency Ratings Are Calculated in Liquid Filtration
Filter efficiency starts with counting particles. In liquid filtration, a test uses a fluid with a known particle size distribution, sends it through the filter media, and counts particles upstream and downstream at a chosen size. Beta ratio is the common way to express that count. Beta at a given particle size equals the number of particles at or above that size upstream divided by the number at or above that size downstream. A beta ratio of 20 means 95 percent of the target particles are captured; a beta ratio of 100 means 99 percent are captured. The percentage is therefore tied to the particle size being counted, not to every particle in the fluid. That calculation explains why a published range such as 95%–99% needs context. The range may reflect different efficiency grades, different test particle sizes, or both. As a manufacturer-stated example, the LCR-500 oil absorbing liquid filter bag from EAST Filtration is listed with 95%–99% filtering efficiency and multiple efficiency ratings. That is a design claim from the manufacturer, and it gives buyers a starting point. A filter bag supplier may publish a range across several grades, while a custom filter bag project may target one narrow condition. The practical meaning comes from the test method: what particles were used, how the fluid was prepared, and what flow rate the media saw during the test.
Why Nominal and Absolute Ratings Change the Meaning of 95 to 99 Percent
Nominal and absolute are two rating words that often appear near efficiency numbers, and they do not carry the same weight. One describes an average result under defined conditions. The other points to a threshold. When a bag is described as 95 to 99 percent efficient, the rating word matters as much as the number because it tells readers what kind of claim is being made.
1. Nominal Ratings Describe an Average Capture Result Under Defined Test Conditions
Nominal ratings usually describe an average capture result. A filter bag may capture most particles around a target size, while some smaller or irregular particles pass through. The rating is not a sharp cutoff. It reflects the media, the test fluid, and the particle distribution used in the test. In practical terms, nominal language is useful for comparing filters that were tested in a similar way. If one bag is described as 95 percent nominal and another as 99 percent nominal, the difference may be meaningful, but only when the underlying test conditions match. A nominal 95 percent rating can still be a strong result for a difficult fluid if the media is matched to the oil, gel, or contaminant load.
2. Absolute Ratings Point to a Maximum Particle Size Threshold
Absolute ratings point to a maximum particle size threshold. In a well-defined absolute rating, the claim is tied to a stated particle size and a test that checks whether particles above that size pass downstream. This is a stronger form of language than nominal, and it is often used when a process needs a clearer retention target. Even so, the rating is defined against a particular threshold under a particular method. If a product description uses absolute wording without naming the particle size, test fluid, or method, the word absolute is doing more work than the number can support. For a 95 to 99 percent range, readers should ask whether the range is nominal, absolute, or a mix of grades.
What Operating Conditions Do to a Published Efficiency Rating
Operating conditions decide how much of a published rating shows up in a real system. Flow rate is the first factor. When flow increases, fluid spends less time in the media, and the local velocity through the pores rises. That can change how smaller or deformable particles are captured. Viscosity is the next factor. A thick oil moves differently from a light oil; it increases flow resistance, can hold particles in suspension, and can change how droplets or gels meet the media. Particle size distribution matters too. A fluid with many particles near the rating size will challenge the filter differently than a fluid with a few large particles and many fines. Fluid chemistry and temperature can also shift how the media behaves and how contaminants stay dispersed. Picture two plants using bags with the same 95 percent rating. One runs a light oil at a modest flow rate. The other runs a viscous fluid at high flow with fine dispersed contaminants. The same printed number can lead to different outlet quality because the media sees different conditions. The LCR-500 example is stated at 95%–99% by the manufacturer, and that range is best treated as a design claim for the product family rather than a fixed result for every oil, flow rate, or contaminant mix. A buyer comparing oil absorbing filter bags should line up the rating with the actual fluid, the expected particle size, and the flow the housing will deliver. The micron values and polymer grade for the LCR-500 example are not established in the available specification, so the efficiency range should be read as the manufacturer’s stated design claim.
Conclusion
Filter efficiency ratings are a compact language for a complex event. The 95 to 99 percent range tells readers that a filter media is designed to capture a high share of target particles under defined conditions. It becomes useful when paired with beta ratio logic, nominal or absolute rating language, and the operating conditions of the actual fluid. For the LCR-500, the manufacturer states 95%–99% filtering efficiency and multiple efficiency ratings; that is the stated design range. Anyone using that number should match it to the fluid, flow, viscosity, and particle size in their process. Read the efficiency number as a defined test result, then compare it with the system where the bag will work.
FAQ
Q：What does a 95 to 99 percent filter efficiency rating actually measure?
A：It measures capture of particles at a defined size under a defined test method. Beta ratio logic counts particles upstream and downstream; 95 percent corresponds to beta 20, and 99 percent corresponds to beta 100 at that target size. The rating is tied to particle size, test fluid, flow, and media, so it is a test result rather than a statement about every possible particle in every liquid. For the LCR-500, the manufacturer states a 95%–99% range with multiple efficiency ratings.
Q：How do nominal and absolute ratings change the way filter efficiency is read?
A：Nominal ratings describe an average capture result under defined test conditions, while absolute ratings point to a maximum particle size threshold. Absolute language is stronger, but it still depends on a stated particle size and test method. When a bag shows 95 to 99 percent efficiency, readers should check whether the number is nominal, absolute, or a range across different grades. That determines whether the number is an average result or a threshold claim.
Q：Can a liquid filter bag keep the same efficiency as flow rate and viscosity change?
A：No. Higher flow reduces fluid residence time and changes pore velocity, while higher viscosity changes flow resistance and how particles or droplets move through the media. Efficiency can shift with particle size distribution, fluid chemistry, temperature, and contaminant loading. A published 95 to 99 percent rating is a reference point from defined conditions. Real performance depends on matching the bag to the actual fluid, flow, and contaminant profile in the system.
Sources / References
Understanding Filter Efficiency and Beta Ratios
Factors to Consider Before an Oil Flush
Glossary of Terms - Water Quality Association
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