This document specifies a procedure for the evaluation of the filterability of dry lubricating oils. The procedure only applies to mineral-based oils, since fluids manufactured from other materials (e.g. fire-resistant fluids) can be incompatible with the specified test membranes. This document is applicable to oils of viscosity up to ISO viscosity grade (VG) 100, as defined in ISO 3448. These oils are widely used as hydraulic fluids, and within the range described, the variation in filterability due to viscosity is included within the precision range of this document. The procedure is not suitable for some hydraulic oils on which specific properties are conferred by the use of insoluble or partially soluble additives, or by particularly large molecular species. These additives include some viscosity index modifiers and some friction modifying additives.

This document can also be applied to oils of ISO viscosity grades (VG) 150, 220 and 320, as defined in ISO 3448, using the specified 3,0 µm rated membranes. These oils are widely used as heavy-duty lubricants in equipment such as paper making machines and rolling mills. Within the range described, the filterability as defined is not dependent on the viscosity of the oil.