ISO codes increase hydraulic system uptime.
For years anybody that has worked in fluid power has known that the number one cause of hydraulic component failure is contamination. It has been reported that anywhere from 75% – 90% of failures are related to contamination. Component failures cause unscheduled system down time that can be extremely costly. In the automotive market these costs are in the thousands of dollars per minute category. A question that you should ask yourself is how much does equipment downtime cost me? If there is so much on the line why do we continue to tolerate premature hydraulic system downtime? In the following paragraphs we will try to take the mystery out of contamination control and briefly outline a common sense approach to help reduce downtime in your hydraulic system.
Where does contamination come from?
Even though a hydraulic system is considered closed, contamination is generated from component degradation, brought in through cylinder rod seals or can be breathed in due to volume changes in hydraulic reservoirs. To simplify this section let us just say that hydraulic systems do get contaminated, causing failures unless we remove the contamination through continuous filtration.
What is the difference between absolute and nominal filters?
In an attempt to rate filter efficiencies, manufacturer’s talked about the ability of a filter to remove particles of a certain micron size. Nominal ratings were arbitrary and were placed on filters by the manufacturer. Absolute ratings were more specific and detailed the ability of filters to keep hard spherical objects of a certain micron size from passing through the filter. Unfortunately contamination comes in all different sizes, not just spherical. These ratings also were not developed from standardized tests.
What is a micron and how does it affect my system?
A micron is a unit of length. Its’ dimension is .001 mm or .000039 inches. As a matter of comparison bacteria is about 1 micron, the lower limit visible to a person is about 40 micron in size and a grain of table salt is about 100 micron. A hydraulic system is adversely affected by particles that can not be seen by the naked eye. In order to keep your system up and running you must remove particles in the 3 micron and above size.
How much contamination can my components tolerate?
All components have some inherent ability to accept some contamination without failure. As a general rule you want the component in your system to fail for reasons other than contamination. Most suppliers will give guidelines as to how much contamination their components will tolerate. Typically, higher pressures and tighter component tolerances require higher degrees of filtration. A very good visual is that a 150 gallon system can have approximately 1000 milligrams of contamination traveling around. That’s equivalent to two extra strength aspirin!
Multi-pass tests and Beta Ratio’s – a good start.
Multi-pass tests and Beta Ratio’s are industry standardized tests run to find out how efficient a filter is at removing contamination from a system. A beta ratio is a comparison on a standardized test of the number of particles greater than a certain size upstream of a filter compared to the number of downstream particles. For example if you had 10 particles greater than 10 micron in size introduced upstream of a filter and you measured one particle down stream, you would have a beta ratio of 10/1 or 10. Beta ratio’s give you a way of comparing how efficient one manufacturer’s filter is compared to another. In theory, a more efficient filter on like systems should provide better results.
ISO class levels – a better way.
Unfortunately we seem to be talking in theory. ISO class levels give us a method of determining what is happening in the real world. ISO class levels are a ruler that allows us to measure how clean a sample of fluid is from an actual system. ISO class levels use particle counters to determine a distribution of particles of a certain size dispersed in a 100 ml fluid sample. In the past, the ISO class determination was made by measuring particles that are greater than 5 micron in size and greater than 15 micron. These numbers are then plotted on a chart and you are given a relative comparison. A rating of 15/11 is very clean while a rating of 20/17 is quite dirty. Each level you go up in class doubles the particle count of 5 and 15 micron particles.
New ISO cleanliness – the best way (so far).
The new ISO cleanliness codes measure particles in the 2 micron size along with the 5 and 15 micron size. This new method also measure particles that are irregular in shape, not just spherical. The new code is denoted as 4μ(c)/6μ(c)/14μ(c).
We believe that too much emphasis has been placed on terminology and not enough on end results. Anybody who has kids can relate to this. You ask them to go up to the bathroom wash up and get ready for bed. When they come down you ask them what they did. They explain that they ran a bath, used soap, clean water and shampoo. On closer examination you end up sending them back up because even though they used quality products they didn’t accomplish the task. In a hydraulic system we have focused too much on microns, absolute, nominal, beta ratio’s etc. instead of what is the goal. We need to focus on achieving a system clean enough so that when there is a failure it is not contamination related. If we achieve that, then in theory we can reduce your hydraulic related failures by up to 90%.
Now that you have an understanding of some of the terminology, you can begin to think about the big picture. What is your goal? It should be to make money by keeping your equipment up and running.
Considering the tools we discussed, how do we use them to achieve our goal of increased equipment uptime.
1. Determine the most sensitive component in your system and the ISO cleanliness code for that component. (Supplied by manufacturer…. Or RHM can provide you with a guideline of ISO cleanliness levels by general component type)
2. Set your target for cleanliness.
3. Develop a procedure for taking fluid samples, a test point in the pressure line of the system provides a quick an easy method.
4. Take test sample and measure the ISO class level.
5. If it meets your target – great. If not put in a more efficient filter run for a few days and retest.
6. If you still do not meet target requirements by improved filter efficiencies (beta ratio) then you need to look at putting more fluid through the filter by means of an external re-circulation pump.
7. After meeting the system requirements re-test every 3-6 months to be sure the cleanliness level is maintained.
By following this simple procedure you will undoubtedly enjoy improved uptime on your hydraulic system. For more detailed information on how you can improve system uptime, your local RHM salesman has been thoroughly trained to go more in-depth into what was briefly discussed in this tech tip.