Sievability and separability are two major criteria which have been used in the past to appraise the performance of filters. Although both criteria have significance in rating filters, it has been demonstrated in practical applications that such ratings cannot reflect the entire spectrum of filter performance. Test data obtained from more than 1200 different filters tested in the past decade at the Fluid Power Research Center at Oklahoma State University indicate that two major intrinsic filtration parameters must be addressed to appropriately and accurately assess the characteristics of a filter. They are separability (power to capture) and retentivity (power to retain).
The Epsilon Rating Method was developed from the Elutivity Theory, which considers the separability (Beta Filtration Ratio), the retentivity (Delta Ratio used to express the degree of particle desorption or caking) and system operating parameters. This rating method has a theoretical basis and provides more accurate results in field applications than other standard filter performance techniques.