Visual Identification of Particulate Contamination Using Patch Testing

In previous posts, we discussed how contamination drives wear, and failure in hydraulic systems.

How do we see contamination when most harmful particles are smaller than the human eyesight limit (~40 µm)?

One simple but powerful method is the patch test. In a patch test, a fluid sample is passed through a fine membrane filter. Particles are captured on the surface and can then be examined under a microscope.

The video below shows how particles from a contaminated hydraulic oil sample become clearly visible once collected on a patch and viewed under magnification, highlighting just how much damaging material can exist in oil that may otherwise appear “clean”.