Filtration, abbreviated as FLTR, is the process of separating solids, liquids, or gases from a mixture using a medium, called a filter, that allows only certain particles to pass through while retaining the others.  The filter medium can be made of various materials such as paper, cloth, sand, or activated carbon, depending on the type of mixture being separated and the desired outcome.  Filtration is used in a wide range of applications, from everyday tasks such as water purification and air conditioning, to industrial processes such as oil refining and pharmaceutical production.  The purpose of filtration is to remove impurities or unwanted particles from a mixture, or to separate two or more components of a mixture based on their physical or chemical properties.

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Filtration Index

• Filtration Design Classification
• Filtration Glossary

Filtration Design Classification

• Air Filtration  -  Air is forced through a mesh in which unwanted substances are removed by getting stuck to the filter and mesh.
• Bag Filtration  -  Settling of the particles in a bag while liquid is poured through the same bag is used for clarification of fluids.  The bags come in a variance of sizes that depend on the matter to be filtered out.
• Cartridge Filtration  -  This eliminates harmful sediments through a cylindrical-shaped cartridge.
• Centrifugal Filtrarion  -  Takes place without any medium.  A circled or rotational movement is made through the liquid or the semi-liquid that is to be filtered, and the velocity of the rotation separates the dense liquid from the productive liquid.
• Cold Filtration  -  Requires liquids to pass through a cold set of filters to remove suspended particles.
• Cyclone Filtration  -  A cyclone is created using an industrial fan to filter out the dust through an air stream.  It is a low-cost form of filtration method and is used very often a variety of industries.  Cyclone filters, also known as cyclone separators, are regularly employed as a pre-filter to remove large contaminants from the air before the stream moves to other filter types. 
• HEPA Filtration  -  This filter is powerful enough to sift micro and nanoparticles such as chemical compounds, viruses, bacteria, and other particulates from the air that passes through it.  A typical HEPA filter is made using tiny meshes of fibers in random alignment.
• Depth Filtration  -  Is a graded density process in which a medium itself collects different sizes of impurities to filter out the key element.
• Gravity Filtation  -  A process where there is no separate medium used but gravity itself.  The flow of the liquid from top to bottom helps in removing solids because of the pressure in the atmosphere.
• Hot Filtration  -  When small sizes of crystal compounds need purification, the impurities in the element are melted out at high temperatures while the liquid is slowly cooled down to get back into its crystal form, separating the unwanted factors of the substance.
• Hydraulic Filtration  -  To filter out petroleum and other similar liquids, some industrial filters are used for purification using a hydraulic system to drain out oil impurities.
• Liquid Filtration  -  This filter is used to separate suspended solids from a fluid stream.  A physical barrier, called the filter medium, is a prerequisite in the filtration process in which the liquid passes through and where the solids are retained.  They are widely used in many solid-liquid mechanical separation processes.
• Mechanical Filtration  -  Uses the force of atmospheric pressure to carry out filtration.
• Multilayer Filtration  -  Frame filters with square filter elements arranged in vertical rows.  They are equipped with a hydraulic lock for pressing the filter pack, a double-acting cylinder with automatic pressure control, a pneumatic drive and a control system.
• Panel Filtration  -  A panel-shaped filter is used very often in ventilation units, and comes in different types and sizes for wide applicability.
• Sand Filtration  -  A process in which the treatment of the water is realised by a porous nature of a sand layer which traps particles present in water.
• Strainer Filtration  -  Closed vessels that collect solid particles to be separated while passing a fluid through a removable screen. 
• Surface Filtration  -  Has a barrier to stop all unwanted particles from reaching the surface.
• UV Light Filtration  -  UV light filtration systems can render organisms unable to replicate and still leave the PH, taste, and color of the water untouched.  UV treatment is necessary to remove various impurities such as ozone, bromine, chlorine, and chloramines, among many organic pollutants from water.
• Vacuum Filtration  -  Vacuum filters use the force of suction to create a static pressure in the vessel through which the dust (and any other unwanted) particles are separated from the usable material.

Filtration Glossary

A

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• Absorption  -  The process of a fluid being taken into the pores of the media.
• Aerosol  -  A dispersion of small liquid particles in a gas.
• Air Filter  -  A device for removing particulate material from an airstream.
• Atmospheric Pressure  -  The pressure exerted upon the earth's surface by the air because of the gravitational attraction of the earth.

B

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• Backwash  -  The upward flow of water through a resin or filter bed in the water treatment process.  It is used to cleanse, expand and regenerate the resin or filter bed.
• Blinding  -  The loading up of the filter medium so as to reduce filtration efficiency.

C

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• Cake  -  The layer of solids deposited in the filter medium during the clarification of a slury.
• Cake Release  -  The ability of a filter medium to allow clean separation of the cake from the medium.
• Calendered Cloth  -  Cloth that has been passed through a pair of heavy rollers to reduce the thickness of the cloth or to flatten the intersections of the wires and provide a smooth surface.
• Capacity  -  The amount of containment that will be collected on a filter before specified restriction level is reached.
• Carbon Filter  -  An air purifier using activated carbon as the air cleaning agent for the removal of gaseous contaminants.
• Cartridge Filter  -  Consist of multiple cylindrical tubes mounted on holders in a pressure tank. The holders seal the ends of the tube so the water must pass through the walls of the cartridges.
• Cellulous Media  -  A filter material made from plant fiber.
• Check Valve  -  These valves are designed to allow the process fluid to flow in only one direction to prevent backflow.
• Cleaning Capacity  -  An air cleaner must constantly re-circulate indoor air in order to effectively reduce concentrations of airborne particulate contamination.
• Cleanroom  -  A room/facility in which the air supply, air distribution, filtration of air supply, materials of construction, and operating procedures are regulated to control airborne particle concentrations to meet approperate cleanliness levels.
• Clean Zone  -  A defined space in which the concentration of airborne particles is controlled to specified limits.
• Contaminant  -  Any foreign or unwanted substance which can have a negative effect on system operation, longevity, or reliability.

D

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• Density  -  The ratio of the amount of matter in an object compared to its volume.
• Diatomaceous Earth Filter  -  Made up of multiple leaf filter screens mounted on a shaft in a horizontal cylindrical tank. Flow is from both sides of each leaf into collector channels leading to the center of the shaft.
• Discharge  -  The liquid that leaves the filter after passing through the filter medium.
• Downstream Pressure  -  The pressure exiting the outlet side of the heat exchanger.

E

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• Effective Area  -  The total area of the filter media exposed to fluid flow.
• Efficiency  -  Is expressed in percentage and always less than 100%.
• Element  -  A porous device that performs the actual process of filtrarion.
• Emulsion  -  A suspension of small liquid droplets within a second liquid that will not mix.
• Emulsion Cleaner  -  A cleaner consisting of organic solvents dispersed in an aqueous medium with the aid of an emulsifying agent.

F

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• Filter Life  -  The duration, time or volume, that a filter can operate effectively between replacement and/or cleaning.
• Filter Medium  -  A porous sheet capable of passing liquid through while retaining solids by means of mechanical separation.
• Flow Rate  -  The amount of fluid that flows in a given time past a specific point.
• Fluid  -  A substance that deforms and changes position when put under stress.
• Fluid Pressure  -  Fluid at rest, exerts a force perpendicular to any surface in comes in contact with.

G

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• Gasket  -  A seal between two components, usually bolted.

H

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• HVAC  -  Used in both residental and commercial systems to controll air quality, humidity, and temperature in indoor spaces.

I

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• Inlet Pressure  -  See upstream pressure

J

K

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• Kinematic Viscosity  -  The ratio of dynamic viscosity to density or the resistive flow of a fluid under the influance of gravity.  

L

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• Laminar Flow  -  Generally happens when dealing with low Reynolds numbers in pipes. This could be due to low velocities, large diameters or high viscosities.
• Line Pressure  -  The pressure in the supply line.

M

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• Media Filter  -  A mechanical filter is a vertical cylindrical vessel that contains some sort filter media. In the oil patch, this will be one to several layers of sand, gravel and/or crushed anthracite.  It may also use walnut shells for the filtration media.

N

O

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• Organic Contaminant  -  Carbon-based chemicals, such as solvents and pesticides, which enter water through cropland runoff or discharge from factories.
• Osmotic Pressure  -  The pressure created by the difference in concentration of the constituents on either side of the membrane, and this pressure drives the osmosis process.
• Outlet Pressure  -  See downstream pressure

P

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• Particulate  -  Solid material suspended in water.
• Permeability  -  The quality of the soil to enable water to move downward through the soil.
• Porosity  -  A measure of the open area of a filter media.  Sometimes called volume of voids.
• Pottable Water  -  Denotes whether water is suitable for human consumption.
• Precoating  -  The operation of depositing on inert material prior to beginning filtration.
• Pressure  -  It is the force exerted perpendicular to the surface of an object and is expressed as force per unit area.
• Pressure Differential  -  The pressure difference between two points of a system.
• Pressure Loss  -  The difference in pressure between two points, usually caused by friction resistance in the pipe, but moisture can also affect it.

Q

R

S

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• Scale  -  Rust or corrosion products adhering to the inner surfaces of pipe.  It can decrease the ability to transfer heat and increase the pressure drop for flowing fluids.
• Sediment  -  Matter present in a water supply, commonly diry or sand, that enters the water due to aging pipes.
• Specific Gravity  -  The density or ratio of any substance to another substance.  It sometimes may be called just gravity or relative density.
• Strainer  -  A closed vessel that collect solid particles to be separated while passing a fluid through a removable screen.
• Supply Air  -  A mixture of re-circulated air and outside air which has been conditioned and delivered to the space.
• Surface Loading  -  The accumulation of collected dust on or close to the upstream surface of filter media.
• Surface Media  -  Filter medias that are thin, cellulosic, microfiber or membrane material and, due to construction, generally provides high flow rate, low pressure rate, and high efficiency, ...
• Suspended Solids  -  This figure is the sum of all of the suspended material found in a water sample or process stream.

T

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• Tackifier  -  A substance applied to filter media to increase the retention of dust.
• Temporary Strainer  -  A startup strainer, also known as a witch’s hat or conical strainer, in installed in a system to remove unwanted debris from the process stream.
• Thermal Sealing  -  A method of joining two or more layers of media together using heat.
• Tracer Gases  -  Compounds such as sulfur hexafluoride, which are used to identify suspected pollutant pathways and to quantify ventilation rates.
• Two-stage Air Cleaner  -  A dust removal system for intake air with a built-in pre-cleaner and an element.
• Turbidity  -  The cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye.
• Turbulent Flow  -  The flow rate at which laminar flow is exceeded and filtration performance is adversely affected.

U

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• Underrating  -  Operating a filter at less than manufacturers stated cfm capacity.
• Uniform Density  -  Having the same weight per unit volume of filter media from the upstream (influent) to the downstream (effluent) side of the filter.
• Unitary Filter  -  Individual filters when joined with others of the same type, form a filter bank.
• Upstream Pressure  -  The pressure entering the inlet side of the heat exchanger.

V

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• Vapor  -  The gas state of a liquid or solid.  Both vapor and gas are basically the same thing.
• Velocity  -  The rate of change or displacement with time.
• Ventilation  -  The introduction of outdoor air into a building by mechanical means.
• Ventilation Rate  -  The rate at which outdoor air enters and leaves a building.
• Viscosity  -  The measure of the internal friction/resistance to the flow of a liquid.

W

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• Water Based  -  A coating in which the film forming ingerdients are dissolved in or suspended in a volatile system containing water as the major solvent.
• Water Desalination  -  The process of removing salt from water for agriculture and to provide drinking water.
• Water Hammer  -  Occurs when a valve is suddenly opened or closed.
• Water Hardening  -  Process of hardening high carbon steels by quenching in water or brine, after heating.
• Water Softener  -  Used to remove dissolved minerals from water.  Hard water can leave mineral scale after evaporation.
• Water Treatment  -  The manipulation of incoming water to make it suitable for the intended purpose.

X

Y

Z

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• Zone  -  The occupied space.