Bubble Point Test

The bubble point test is the differential gas pressure at which the first steady stream of gas bubbles is emitted from a wet filter element under specified conditions. The air pressure required to blow the first stream through a pore is inversely proportional to the size of the largest pore in the element.

Dirt Capacity Test

The dirt capacity test determines the weight of a specified artificial contaminant which must be added to the influent to produce a given differential pressure across a filter at a specified condition. It is used as an indication of relative service life.

Multi-pass Test (i.e. ISO 16889)

The multi-pass test is used to determine the Beta Ratio/micron rating and dirt holding capacity of a filter element and is a destructive test.

Patch Test

Visual analysis of a fluid sample. Passing a fluid through a fine media patch. The patch is then analyzed under a microscope.


Viscosity is the measure of a fluid’s resistance to flow. Fluids that have a high resistance to flow have a high viscosity. Fluids that have a low resistance of flow, have a low viscosity. Fluid viscosity changes with variations in fluid temperatures.

Pressure Drop (Differential Pressure, or Delta P)

A difference in system pressure between the upstream and downstream sides of the filter.
Four Major Factors Contribute to Pressure Drop:

  1. Filter Media
  2. Dirt Contamination
  3. Flows (higher flows create higher pressure drop)
  4. Fluid Viscosity (higher fluid viscosity’s mean higher pressure drop)