An Investigation of a Mass Flow Rate Method for Evaluating the Filterability of Hydraulic Fluids

Fine filtration is used in modern systems to remove built-in contaminants, wear debris generated within the machine and dirt entering the fluid from the environment. The ability of the fluid to retain its filterability properties is critical for efficient, reliable machine performance. This is particularly true for biodegradable fluids used in environmentally sensitive areas. ISO 13357:1 and ISO 13357:2 are internationally accepted methods for evaluating the filterability and compatibility of hydraulic fluids. This method uses a manual procedure for measuring the volumetric flow rate of a fluid as it passes through a 0.8µm filter membrane. In this research, hydraulic fluids and lubricants of various base oil and additive composition were evaluated using a modified version of ISO 13357 that utilizes mass flow rate measurements to assess fluid filterability. A comparison of volumetric and mass flow rate filtration ratios reveals that the use of mass flow rate to determine filterability yields comparable results while improving test repeatability. These findings are the basis for a new ASTM standard methods proposals for the measurement of fluid filterability and compatibility.