ISO Hydrocarbon Standards
ISO (International Organization for Standardization) is an independent, non-governmental membership organization and the world’s largest developer of voluntary International Standards. ISO standards provide a set of principles across industries to accurately evaluate and determine quality levels of particular products. For our purposes, we are most concerned with hydrocarbon fluid cleanliness levels and filter ratings. Accurate benchmarks across all industries are important requirements for purchasing, planning and maintaining and servicing equipment. ISO standards are typically reviewed and updated every 5 years.
The ISO cleanliness code (1SO4406) is used to determine contamination levels per ml of fluid at 4m, 6m and 14m. It is then expressed in 3 numbers, (ie. 15/18/20) where each number represents the largest size of a contaminant present.
25/22/19 is a common ISO code for new oil, but this level of contamination is too high for hydraulic or lubrication systems. Why would the ISO allow oil to be given this cleanliness code if it is not acceptable for an important part of equipment?
The ISO standards were created in the late 1970’s when our equipment had lower equipment component tolerances (over 10 microns). Filtration technologies back then were adequate to protect the equipment. In present day, equipment component tolerances are very tight, as most engine components are under 8 microns, bearings are under 3 microns and hydraulic system components are under 1 micron. In order to properly protect our equipment we need to be able to filter 4 microns and below.
The Problem: Traditional filtration is unable to remove contamination under 3 microns with any realistic efficiencies. The ISO standards for cleanliness start analysis at 4 microns, therefore they are not providing all the information to identify possible severe contamination issues. This misinformation reduces the effectiveness of proactive maintenance practices, and reduces the ability to protect integral business assets.
Multi-Pass Testing ISO 16889
In 1999, ISO introduced the ISO 16889 set of standardization for Multi-Pass testing on Filters. Previously, the only performance data a manufacturer had to publish about the filter was based upon its ability to remove 10 µm particles. These new procedures were designed to provide greater precision in particle contamination measurement, so consumers could accurately compare the particle removal efficiency between filter manufacturers. The Multi-Pass system testing, sends artificial contaminants through manufacturers filters and measures the size of contaminants captured. They repeat this process 12 or more times, and then from that they calculate the average size of contaminants collected and develop the ISO code and a beta ratio. The beta ratio is defined as the particle count upstream divided by the particle count downstream at the rated particle size. For example: a 5 micron filter has a rating of beta 10, which means that it will have on average 10 particles larger than five microns upstream of the filter, for every 1 particle 5 microns or greater downstream. The efficiency of the filter can be calculated directly from the beta ratio because the percent capture efficiency is ((beta-1)/beta) x 100. A filter with a beta of 10 at five microns is thus said to be 90 percent efficient at removing particles five microns and larger. From this procedure and rating consumers can quickly see how the filter performs over a specified range of particle sizes and can compare the performance of candidate elements. However….
ISO: 16889 Better but Still Flawed
This approach although it has been significantly improved from the last ISO standardization, IS STILL flawed. This Multi-Pass method should instead be turned into a one-pass test system to get the most accurate filter rating. This is because the more contaminants that enter a system, and the more that collect on the filter, the better it collects. So by placing a new filter in a system, it will not entirely collect the submicron particles as efficiently until there is a layer of contaminants already collected on the filter. Therefore a multi-pass test isn’t as accurate as it leads the public to believe, because the more passes of contaminants that occurs, the greater the collection of particle contaminants. A single-pass system would be the best approach to accurately measure particle contaminants collected for filter ratings.
It is also to important to remember, that when using beta ratios to compare filters they do not inform the consumer about::
- How it will perform in real world conditions with flow rate and temperature changes
- The dirt-holding capacity of the filter
- The total amount of contaminants that can be trapped by this particular filter
- It can give misleading statements about Absolute Filtration Ratings
Nominal vs. Absolute Filtration Ratings
Nominal Filtration = the SMALLEST size particle that may get trapped.
In other words, the smallest particle a 25 micron nominally rated system can trap is 25 microns. However there is no standardized accepted industry standard to determine the nominal micron rating of a filter.
Absolute Filtration= the LARGEST particle size that can get through the openings in the filter element
Absolute in the dictionary means:”
Referring back to the above example:
- Absolute filter rating equation= [(beta – 1) / beta] x 100
- A filter with a beta of 10 at 5 microns= 90% efficiency
This means that the filter’s absolute rating= 90% efficient at removing contaminant particles 5 microns and larger.
This statement creates a lot of confusion between other industries and the filtration industry. The reason for this, is that statement does not mean that the filter removes 90% of the contaminants in the system. It only means that the filter is 90% efficient at removing contaminant particles 5 microns and larger. It also doesn’t refer to the particles under 5 microns; and if your system (100%) is contaminated by 80% of under 5 micron particles, this will not be helpful to removing contaminants from your system.