Filtration is one of the main functions of a filter –drier. But how does it occur? Some systems have just one method and other use combination of methods. There are two types of filtration - one is surface filtration and the other is depth filtration.

The former happens through the screen. The screen is a finely woven mesh that will trap particles that are bigger than its pores. When the screen has captured enough particles, it transforms into depth filter.

In depth filtration, there are multiple porous layers with depth that are used to trap the solid contaminants from the liquid. The channels are tortuous in this case. Here the particles are retained throughout the medium as opposed to on the surface. Depth filters are able to screen a high quantity of particles. In case of a filter drier, the accumulation of contaminants over the screen will make filtration system act as a depth filter. As the contaminants fill the entire mesh they will now start accumulating as layers. This layering of contaminant will continue until the pressure drop across the screen. The pressure drops and reaches a point at which the refrigerant flashes into vapor.

Filters of filter-dryer are of various types -

• Bonded desiccant cores
• Rigid fiber glass filters bonded with phenolic resin; and
• Fiberglass pad filters.