Filter pore size rating was initially done by studying the size of particles that passed through. For micro-filtration, this was done utilizing bacteria of a known colony for the size exemplar. Retention of these bacteria under standardized conditions of flow was the criterion. For standard filters that are not sub-micron rated, yes, there are other standards of particle size that can be and are applied. Nominal rating means that for the nominal rating, a significant percentage of that sized particle will be retained. If a filter has an absolute rating, then it has been demonstrated that none of the particles of the rated size will pass (99+% retention).
Published by James Stewart
Filter pore size rating was initially done by studying the size of particles that passed through. For micro-filtration, this was done utilizing bacteria of a known colony for the size exemplar. Retention of these bacteria under standardized conditions of flow was the criterion. For standard filters that are not sub-micron rated, yes, there are other standards of particle size that can be and are applied. Nominal rating means that for the nominal rating, a significant percentage of that sized particle will be retained.
If a filter has an absolute rating, then it has been demonstrated that none of the particles of the rated size will pass (99+% retention).