Hydraulic Design & Consulting: Technical Notes

The Real World of Filtration

We all know that new oil is dirty oil, and should be filtered before use in hydraulic systems. However, do we really know how dirty new oil really is, and how well a filter cart will clean up new oil before use. We have a hydraulic system that runs at 4500-psi, and we normally try and keep it clean to ISO 14/13 level because of some very expense piston pumps. We have a filter cart with a 5 micron filter, then into a 3 micron filter, used to transfer new fluid into our hydraulic system. So, we took two oil samples, one before use on the new oil just to see how dirty our new oil was (sample #1), it came back at 18/15 with the 5 micron and 15 micron in the critical range. Not all that bad for new oil, I have seen much worse, and was please to find this level on a 275 gallon tote.

We then ran one pass through our filter cart with new filters installed, and took our second oil sample (sample #2). It turned out to be 18/14 with some improvement in the 5 micron range, and more improvement in the 15 micron range. However, the filtration level did not improve to near the level we expected or wanted. Had we used one pass filtration and placed this oil into our hydraulic system, we would have placed stress on our existing system filters to remove contamination to bring our ISO code back up to 14/13 level. Simply put, we were going to be replacing 2, 3 and 5 micron expensive filters in our hydraulic system in short order.

Of course the instructions came back to place the filter cart on the bulk oil tote for several hours to clean up the level to or at what we required for our hydraulic system. With pumps costing $60,000 plus and build to order lead time of 1-1/2 years, it made good sense to make sure we were not the cause of pump failures. Lessons to be learned:

Know how dirty your new oil really is as delivered
Know what level your hydraulic system needs to run at
Use and know how to read oil reports

Ok, some of you are thinking fine, but I do not have a million dollar hydraulic system, just an old wood splitter? The dirty oil you put into your splitter caused a pump, valve or cylinder seal failure, it’s in the shop for two weeks for repair. You lost power, have no heat, no split wood, and while you’re using your splitting mall standing in -20 degree weather splitting wood, you think…

How’s this working out for me?