The quality of the products installed was high and therefore the cartridges were not considered, so the focus was placed on any damages and / or on the block of the bypass valves, filters or other by-pass points. This point was immediately excluded, given that the problem was presented on all machines, making it very difficult that all the systems shown the same defects. After verifying the correct operation of the by-pass valves and the correct equivalence of cartridges, we decided to replace them on a machine, to verify that there had been no problems on the production lot. We removed the cartridge, but we found soon that it goes out very easily from the filter housing. So we checked the cartridge inner diameter, also considering the OR Ring thickness, that makes radial sealing for the intake side of the filter housing, finding an Increasing of 1mm in diameter, with respect to the inside diameter of the original cartridge.