Recent developments in oil filter test methods

Standardized filter test methods facilitate comparisons of different filter products. The multipass filter test is the basis for many oil filter test standards and its reproducibility has been continually improved through better specification of the test conditions and improvements in particle counting methods. Particle counting is a major source of interlaboratory variability. In response, ANSI/(NFPA)T2.9.6R1-1990, a particle counter calibration method utilizing latex spheres suspended in oil, was recently adopted by the USA. The new method provides traceability to internationally accepted definitions of the metre unobtainable by the old method of AC fine test dust calibration. However, the new method is sensitive to subtle instrumental differences. A hybrid method is needed to improve agreement between laboratories and instruments. Other ways of improving reproducibility and communicating test results are also discussed.