Can string wound filters cause foaming?
Answer – No, and Yes. The widely believed urban legend that oil left on the fibers of cotton filters can cause foaming is only partially true. Any oil that contains a fraction that is soluble in amines can cause foaming if that soluble fraction acts as a surfactant (detergent). In the cases we’ve seen where the filters appeared to be responsible for foaming the root causes were always soluble contaminants. The filters looked like the culprits, but were actually helping the foam form indirectly by removing the antifoam, either by itself or as a sticky antifoam-solids agglomerate. Activated carbon beds can do the same thing.
