General Introduction to Liquid Filtration

All filtration and screening involves limiting the passage of various sized solids by means of a barrier or fabric or media. This is done in two ways, by depth filtration using graded density material called felt or by surface filtration using filament woven material called mesh. Wovens, in turn have two basic varieties: multifilament and monofilament. In any application, variables such as flow volume, solids loading, shape and density of contaminants and other factors make this an inexact science. A general description of separation methods of media is helpful.

FELT

This is a filtration media made from a matrix of small fibers. One side is heat bonded to provide a uniform surface free of fiber loss. Contaminant particles are contained within the media by impingement and entrapment. "Porosity" is defined by nominal micron ratings (1, 5,10,25,50,100,200) indicating the largest particle that can pass through, in general, and reflecting an increase in the density. This fabric does not produce an absolute filtration but rather a range based on generally accepted industry tests. Many factors influence the actual filtration including the shape, size, consistency and loading of the contaminates. Also, the feed pressure and rate of flow affects the filtration results. These felts have a far higher dirt capacity and flow rate than a flat woven type bag and is much more resistant to blinding (clogging). The material is meant to be disposable and does not clean as well as a woven material.

PTFE MEMBRANE SURFACE FELT

This is a filter media having a "Teflon" microporous membrane applied to a base of polyester felt. This results in a nonstick surface which allows for a contaminant "cake" to build and slough off or be removed by cleaning.

PEMU - MULTIFILAMENT MESH FABRIC (POLYESTER)

This is a two-dimensional square-woven fabric used for light filtration and general purpose screening. Consistently woven using a given number of threads per inch, its filaments are comprised of small fibers, twisted into threads. It is generally made of polyester polymer. "Porosity" is defined in broad divisions of hole size, measured in microns (i.e. 100, 150, 250, 400, 600, 800). This mesh does not produce an absolute filtration but rather a range based on generally accepted industry tests. Many factors influence the actual filtration including the shape, size, consistency and loading of the contaminates. Also, the feed pressure and rate of flow affects the filtration results. These woven materials are easier to clean than felt materials.

NMO - MONOFILAMENT MESH (NYLON)

A two-dimensional square of woven mesh fabric used for lower solids or higher accuracy screening and classification of solids. Made from a smooth uniform, one piece extruded thread woven into a screen with high accuracy and consistency. Used for exact separation. "Porosity" is defined by a hole size in microns, with greater variety than multifilaments (i.e. 25, 50, 75, 100, 120, 150, 175, 200, 250, 300, 400, 500, 600, 800).