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"When we sent several duplicate oil samples to our oil analysis lab, the particle counts were quite different. Some differed by as much as five in the ISO code. The samples taken after the 7-micron absolute filters were higher than the before samples. How can you determine what the real particle count is so you can make the best decisions?"
Many variables can affect particle counts in oil analysis results. If you test oil in a machine that has just had an oil change or top-up, the particles in the sample will be diluted, producing false data. Likewise, collecting an oil sample when the machine has been down for more than 10 minutes can result in incorrect data, as the large particles will have already begun falling out of the oil and into the sump.
To obtain an accurate picture of the lubricant's health as well as what is occurring in the machine, you should only take samples before the filters. Sampling after the filter only offers an indication of how efficient the filter is performing. Waiting too long to replace your filters or changing them before they are in bypass mode can dump contaminants back into the oil, causing particle counts to skyrocket. These free particles can also wreak havoc on machine surfaces.
For good, reliable data from your oil analysis program, you must be consistent in how oil samples are collected. Make sure you sample from the same point at the same time using the same method every time. The sampling equipment should be clean and dry, and the sample bottles should not be opened until absolutely necessary.
Before you take a sample, clean the machine's sample ports with a lint-free cloth so as not to add to the particle count. It is also a good idea to use a new zip-lock plastic bag to open and close the sample bottle. This will help keep environmental dust and moisture out of the sample. Remember, if you don't control what is going into the sample bottle, you will never have dependable results.
If you send out samples to be tested, you must be able to trust the data you receive from the laboratory. Having a reliable testing facility is just as important as taking samples in the field. If the facility is nearby, make a surprise visit to see how samples are processed and how clean the facility is. If the lab is not handling samples correctly, the test results will be distorted, and you will get false positive data.