Filtration Glossary

Absolute Filtration Rating: The diameter of the largest hard spherical particle that will pass through a filter under specified test conditions. This is an indication of the largest opening in a filter element.

Axial seal (Air) – Utilize a gasket to maintain a seal on the outlet end of the air cleaner housing.

Adhesive A bonding material which provide leak-proof bonding between end cap &  filter media.

Anti-Drain Gasket/Valve – Prevents oil from flowing back out of the oil filter, through the inlet holes, when the engine is shut off.

Absorption : The process of a fluid being taken into the pores of media.

Beta Ratio : The ratio of the number of particles of a given size and larger upstream of a filter to the number of particles of the same size and larger downstream.

Bottom Assembly – Assembles tapping plate and bottom ring.

Bottom Ring – Provides a groove for the sealing gasket and a flange for lockseaming to the filter body.

Bubble Point: The differential gas pressure at which the first steady stream of gas bubbles is emitted from a wetted filter element under specified test conditions. A form of filter element fabrication integrity test.

Bypass Valve (Relief Valve): A mechanism to assure system fluid flow when a pre-selected  differential pressure across the filter is exceeded; the valve allows all or part of the fluid flow to bypass the filter element.

Collapse Pressure: The maximum pressure that an element can withstand without permanent deformation. 

Capacity – The amount of contaminant that will be collected on a filter before specified restriction level is reached.

Centre tube – Provides structural support to the centre of the media to prevent media collapse.

CFM – Measurement of air flow in cubic feet per minute.

Differential Pressure: The difference in pressure across any two points of a system or component.

Disposable: A filter which is intended to be discarded and replaced at the end of its service life.

Dust Holding Capacity: The weight of a contaminant fed to the filter during a test to reach a predefined Terminal pressure drop.

Effective Area: The total area of the filter medium exposed to fluid flow.

Efficiency: The ability of a filter to remove a specified artificial contaminant at a given contaminant concentration under specified test conditions. Expressed as a percentage.

Element: The porous device that performs the actual process of filtration.

End Cap / End Disks – Encloses the filtration media on its ends.

External Gasket – Creates seal with engine mounting base when installed.

Filtration: The physical or mechanical process of separating insoluble particulate matter from fluid, such as air or liquid, by passing the fluid through a filter medium that will not allow the particulate to pass through it.

Fluid Compatibility: The suitability of the filtration medium and seal materials for service with the fluid involved.

Filtration Efficiency: That fraction of suspended particles retained by the filter.

Filtration Area  Area of the filtration media.

Filter Body / Can  - Outer shell of the filter.

Filter Life: The duration, measured in time or volume, that a filter can operate effectively between replacement and / or cleaning.

Filter Cartridge – Assembly consisting of the filter media, end disks/cap, adhesive and centre tube.

Flow Rate: Measure of the amount of fluid passing through the filter. This is always a variable of filter area, porosity, contamination and differential

Housing: A ported enclosure which directs the flow of fluid through the filter element.

LPM Measurement of lube flow in liter per minute.

Media – Material that removes contaminants.

Media Migration : Contamination of the effluent by fibers or other material of which the filter is constructed.

Mean Filtration Rating: A measurement of the average size of the pores of the filter media.

Multi-Pass Test: The test used to determine the beta ratio of an element.

Nominal Filtration Rating: An arbitrary micrometre value indicated by a filter manufacturer. Due to lack of reproducibility, this rating is deprecated.

Non-Woven: A porous web or sheet produced by mechanically, chemically or thermally bonding together polymers, fibers or filaments.

Overall Efficiency (Air) – The percentage of contaminant removed from intake air

Pore Size: Filters are rated according to the size of particles they can remove. Particles which are bigger than indicated pore size, are removed. Smaller particles pass through the media. The size of particles is measured in micro-meters or "microns" one micron being equal to one-millionth of a meter or one-thousandth of a millimeter.

Pressure drop – Pressure on the clean side minus pressure on the dirty side. It can also be called as the difference in pressure between two points, which is usually measured between inlet and outlet service of the filter housing.

Primary Air Filter / Outer Element – element that removes around 99.9% of the air’s dust.  The air flows through the primary filter first.

Permeability: The relationship of flow per unit area to differential pressure across the filter medium.

Pleated: A filter element whose medium consists of a series of uniform folds and has a geometric form of a cylinder, cone, disc, plate, etc. Synonymous with “convoluted” and “corrugated.”

Pore Size Distribution: The ratio of the number of holes of a given size to the total number of holes per unit area expressed as a percent and as a function of hole size.

Porosity: The ratio of pore volume to total volume of a filter medium expressed as a percent.

Rated Flow: The optimum flow rate for which a filter is designed.

Radial Seal (Air) – Utilizes urethane end caps to maintain a seal on the inner diameter of the filter and the outside area of the outlet tube.

Relief Valve / Bypass Valve – Relieves excess differential pressure.

Restriction  - Resistance to flow.

Retainer / Spring – Exerts pressure on the filter cartridge to the bottom assembly, maintaining an internal seal.

Safety (Secondary) Air Filter / Inner Element – Optional filter that protects the engine during service of the primary filter and in case of a leak in the primary filter.

Spin On Filter Throw away type of filter.

Tapping Plate  - Portion of the filter that contains the threads.

Thrust Spring A coiled spring placed between filter bowl & bottom cap of the filter element to keep the element securely at its place inside a spin on filter.

Two-Stage Air Cleaner – dust removal system for intake air with a built-in pre-cleaner and an element.

Upstream Side: The feed side of the filter.

Viscosity: A measure of the resistance to flow of a liquid. Viscosity of a liquid varies appreciably with changes in temperature.