Glossary of Filtration Terms

Glossary of Filtration Terms

Backwash – The process of cleaning the filter medium or septum by reversing the flow of water through the filter.

Basecoat – A layer of filter aid between the precoat and septum.

Blinding – Filling in and clogging of a filter medium caused by entrapment of particles from a filtered liquid. When the medium becomes “blind,” an increase in different pressure and reduction in flow results.

Bridging – Debris which arches, or bridges, the individual pleats in the filter cartridge.

Cartridge Filter – A filter that utilizes a pleated, porous medium as a filtering material.

Clarification – The process by which the filter removes progressively smaller particles on each successive turn over, thus improving efficiency and extending the cycle life. Cartridge filters use the clarification process.

D.E. – Abbreviation for diatomaceous earth. Fossil-like skeletons of microscopic water plants called diatoms.

Differential Pressure – (1) The difference in pressure between two given points. (2) The combined pressure caused by debris, filter cake, precoat and septum, expressed as AEP (“delta P”). (3) The effluent pressure minus the influent pressure.

Effluent – Fluid which has passed through a filter. Also called the filtrate.

Enzymes – An organic protein, also known as amino acids. Enzymes are non-toxic and biodegradable. Although they are not an oxidizer or clarifier, enzymes significantly reduce cartridge maintenance by breaking down oils into carbon dioxide and water.

Feed – The mixture of particles and fluid that is introduced into the filter. Terms used synonymously include “influent” and “incoming slurry.”

Filter Aid – Any material (usually diatomaceous earth) that enhances the separation of solids from liquids in the filtration process.

Filter Cake – The combined layers of solids, precoat, and debris removed in the filtration process and accumulated on the surface of the filter medium.

Filter Cycle – The operating time between cleaning or backwash cycles.

Filter Medium – The permeable material such as diatomaceous earth, sand, or polyester non-woven material used to separate suspended particles from liquid.

Filtrate – Fluid that has passed through a filter. Also called the effluent.

Filtration – The process by which particles are separated from a liquid by passing through a permeable material.

Filtration Rate – Flow in gallons per minute (GPM) through one square foot of filter medium. For residential pools, the filtration rate should be 2 GPM per square foot of D.E. filter surface area and 1 GPM per square foot of cartridge filter surface area. For most commercial pools, the filtration rate should be 1 GPM per square foot of D.E. filter surface area and .375 GPM per square foot of cartridge filter surface area.

Hydrophilic – Water accepting. The ability to absorb water.

Hydrophobic – Water rejecting. Lacking affinity for or ability to absorb water.

Influent – Dirty or unfiltered water introduced to the filter. Also referred to as “feed” or “incoming slurry.”

OEM – Original Equipment Manufacturer or brand name.

Permeability – Expressed in cubic feet per minute (CFM), the resistance to flow through a media. The lower the perm number, the greater the resistance. The permeability of a filter media is a quality control measure for cartridge and D.E. filter materials.

Polyester – Long chain synthetic polymer composed of at least 85% by weight of ester of dihydric alcohol and terephthalic acid.

Porosity – (1) The degree of open area between the fibers. (2) The void area which exists in the structure.

Precoat – The layer of filter aid (usually D.E.) formed on the media surface by introducing a slurry (generally between .1 and .2 lbs. per square foot of surface area) to the medium at the beginning of the filter cycle.

Turbidity – (1) The characteristic or property of a liquid that causes it to absorb or scatter light. (2) A measurement of water cloudiness or haziness caused by micro-organisms, algae, or suspended fine particles.

Glossary of Filtration Terms provided by Filbur Manufacturing –

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