What is millipore value?
The Millipore value is the mass of residual particulate found on a component after a standardised extraction wash, captured on a membrane filter and weighed — reported in milligrams per part or per square metre. It is the standard cleanliness specification for bearings, injectors and hydraulics.
Also called: millipore test, residual dirt analysis, gravimetric cleanliness
The test is deliberately destructive of information rather than of the part: the component is washed under controlled conditions, the extraction fluid is drawn through a membrane filter of known mass, the filter is dried and weighed, and the difference is the contamination that was on the part.
Most automotive and bearing specifications go further and require particle sizing under a microscope or automated optical scan, because a single 400 µm hard particle in a hydraulic circuit matters far more than the same mass spread as fine dust.
Meeting a Millipore spec is a process achievement, not a chemical one. It needs the right chemistry, but also filtration on the wash and rinse, controlled drag-out, clean handling and clean packaging — recontamination after the wash is the most common reason a good bath still fails the test.
