From the Sourcebook For Used Oil
Elements

Unfiltered or poorly filtered oil eventually results in growing concentrations of wear debris. The problem is mutually compounding in that the dirtier the oil the more contaminated the oil continues to become from internal wear debris production and destruction to contaminant exclusion seals. While it is always good advice to maintain clean lubricants from a proactive maintenance standpoint (affirmative action), it is equally good advice for predictive maintenance (early wear detection). A failure to do so usually leads to the alarm signal effectively being "lost in the sauce." This concentrated debris results in a high noise threshold, and when an incipient wear signal occurs it will write "in the noise" and be lost (signal-to-noise is less than 1:1). This is a persistent problem with splash-fed gearing, crankcase lubes, and bath lubricated bearings.

Conversely, a clean oil provides not only a healthy and unabrasive lubricating environment but also allows the wear signal (incipient debris generation) to write above the noise level (signal-to-noise is greater than 2:1, for example). When the fluids are maintained clean and if sampling is carried out in live zones (before filters, on bearing drain lines, and at turbulent fluid zones) the early detection of wear anomalies is typically achieved. There is often a need for the routine use of portable filtration systems or retrofitted side-loop filters.

More about the Sourcebook For Used Oil
Elements

Filter/coalescers work by letting oil pass through wetted membranes which keep water out. The media is typically fiberglass type material which has a very high surface area and fairly dense pores. Coalescers take out free water, but cannot take out dissolved water. They work best with low viscosity fluids.

The presence of dirt in an oil is likely to cause a ratio of 5:1 silicon to aluminum in a used engine oil. This ratio can be used to confirm that these elements are associated with dirt contamination.

The Beta Ratio filtration rating is the result of the ISO 4572 Multipass Test Procedure. This procedure calls for the release of contaminant upstream of the filter. As the contaminant is circulated through the element, pressure drop and particle counts are monitored in a controlled manner.

This test will not only determine the size of particle the element will remove, but also its dirt-holding capability and efficiency at different pressure drops. The Beta Ratio is nothing more than a number of particles of a specific size counted prior to the filter divided by the number after the filter. This then gives you an indication of the element’s efficiency.