Air & Gas Filters
Crossflow Membranes
Ion Exchange Filters
Liquid Process Filters
General Information
Glossary of Terms


Common Conversions

Absolute Rating Micron size of a particle that will be removed by a filter at the stated efficiency
Absorption The movement of a liquid or gas into the pores of a solid.
Adsorption A liquid or gas being held on the surface of a solid
ACFM Actual Cubic feet per minute
ASME Code Fabrication standards of American Society of Mechanical Engineers
ASTM The organization called "The American Society for Testing and Materials"
Activated Carbon Granular carbon that has been treated to enable the absorption of odor, taste and chlorine
Aeration The mixing of air with water to achieve mixing or oxidation
Aerosol The dispersion of solid or liquid particles in air that will stay dispersed for a period of time
Agglomerate The aggregation of smaller particles into a larger one
Alkalinity The ability to neutralize acids.  Usual pH is between 7 and 14.
Anion An atomic particle with a negative charge
Antimicrobial Any compound that kills or inhibits micro-organisms on contact
Atmosphere A unit of measure of pressure
Backwash Flow through a filter in the reverse direction
Bacteria A large variety of single celled micro-organisims that lack a nucleus.
Baffle A device which is used in filter housings to divert the incoming stream to provide uniform flow
Bar A designation of pressure units; 1 Bar = 14.5 psi
Beta Ratio The filtration ratio which is the ratio of the number of given size particles in the feed divided by the number of particles of the given size in the effluent
Binders In filtration, these are the compounds which "bind" the fibers together
Blind Spots Areas of a filter media that will not permit flow due to plugging or blinding.
Blinding The pores, or openings of the filter media, are blocked which prevents flow
Body Feed The continuous feeding of a filter aid to the influent stream to create a permiable filter cake
Bridging The formation of a particle "arch" over an filter pore opening
Bubble Point The pressure drop required to expel the first steady stream of bubbles from a wetted filter
Bubble Point Test The intergrity test for filters that is non-destructive and indicative of the pore size rating.
Burst Strength The ability of a filter medium to resist rupture by pressure applied in the normal direction of flow.
Bypass A fluid flowing through a passage other than through the filter media
Cake The surface accumulation of solids on a filter medium.
Cartridge Filter A cylindrical element, usually disposable, which is inserted into a filter housing.
Cation An atomic particle with a positive charge
Caustic Soda A trade name for Sodium Hydroxide, NaOH.
Cellulose A fibrous, vegetable material used as a filter medium
CFM Cubic Feet Per Minute
Chelating Agent A soluble, organic molecule which will hold metal ions in solution
Chloramine A chlorine/ammonia compound which demonstrates greater persistence than chlorine alone.
Chorination The addition of small amounts of chorine gas to water to disinfect the water
Chlorine A chemical compound, Cl2, used in small amounts to disinfect or oxidize.
CIP (Clean-In-Place) The chemical cleaning applied to a fouled membrane to restore it to its original flux performance
Clarification/Clarity Filtration of fluids containing a small amounts of particles
Classification The separation or arrangement of particles by size
Collapse Pressure Pressure which is great enough to collapse a filter
Colloid Submicron particles held in suspension in fluid and will not settle out
Compressibility The degree of change in volume when subjected to pressure
Concentrate (Retentate) The non-filtered stream leaving a membrane filtration system. 
Concentration 1) The amount of material in a unit of volume; or 2) To increase the dissolved material per unit of volume.
Concentration Factor (CF) Ratio of feed mass to concentrate mass.
Concentration Polarization An accumulation of excess particles in a thin layer adjacent to the membrane surface.
Condensate Vapor which has coalesced into a liquid state.
Conductivity The ability of a liquid to conduct an electrical current.  The inverse of resistivity.
Contact Time The time it takes an absorbant to be in contact with a liquid to remove a contaminant
Contaminant Particles in a fluid which are undesireable
Cross-flow Filtration A mode of filtration in which the pressurized feed stream flows parallel to the membrane surface
Cross-flow Velocity Average velocity of the bulk cross flow parallel to the membrane surface.
Crypto Cryptosporidium, a parasite found in water
Cycle (Length) The duration of a filters service before regeneration or replacement is required
Deionization (DI) The process of removing ions from a fluid by an insoluble exchange medium
Density Mass per unit volume
Depth Media Filtration media which removes particles within the media as opposed to the surface
Diatomaceous Earth (DE) A naturally occuring soft, chalk like sedimentary rock which crumbles easily to a powder which is used as a filter medium.
Differential Pressure
(Delta P)
The difference in pressure between two points in a filter system, normally the inlet and outlet nozzles.
Diffusion-Limited Flux
A limit where the flux will no longer increase proportionally with pressure.
Dirt Holding Capacity The weight of material retained by a filter to a given pressure drop
Dirty Differential Pressure The delta P at which the cartridge will  require maintenance or changeout
Disinfectant A chemical compound which is used to sanitize tanks, pumps and piping.
Dissolved Solids After filtering a fluid, this is the residual solids left after evaporation
DOP Test Dioctyl phthalate (DOP).  Standard test to qualify HEPA Filter @ .3um @ 99.97%
Double Open End (DOE) A filter which requires a housing with knife edge seals to seal against the flat gaskets at both ends of the filter element.
Efficiency Under given conditions of contaminant and concentration, it is the percent ability to remove the contaminant.
Effluent The name of the stream as it exits a treatment system
Emulsion A suspension of small liquid droplets within a second liquid that will not mix
Element The unit comprised of the filtration medium and it’s support structure that goes into a filter housing.  Also referred to as the cartridge, filter tube or candle. 
End Cap The closed end of a filter element, pipe or housing.  It may be closed or ported.
Effective Area The total area of medium exposed to flow and usable for separation
Endotoxin A lipopolysaccharide from the walls of a nonviable bacterium; also, a pyrogen
Endotoxin Units (EDU) A unit of measure (EDU) used to express endotoxin (pyrogen) levels
EPA United States Environmental Protection Agency
Extractables In filtration, these are compound that leach into the filtrate.
FDA United States Food and Drug Administration
Feed The input fluid to a treatment process
Filter The complete device which supports the medium carrying out the process of filtration.  The term includes the housing and the element.
Filter Aid A precoat of insoluble media on a filter septum to assit in filtration
Filter Cake The accumulation of solids on a filter septum which builds up and assists filtration
Filter Medium
(Media plural form)
A permiable media which permits fluid flow through it and retains particles
Filtrate A fluid which has been through a filter medium
Filtration The process of removing solids from a fluid stream by means of a septum.
Filtration Efficiency Under given conditions of contaminant and concentration, it is the percent ability to remove the contaminant.
Filtration Rate The volume of fluid that passes through a given area of a filter in a specified time.
Flux (J) Permeate flow rate per unit of membrane area. (e.g., GPM/ft.2/day).
Fouling A deposition of retained solids on a membrane surface or in the pore structure of the memebrane
Frazier A test which measures the air permiability of a filter septum.
Free Water Refers to captured water in a separation system.  Usually a coalescer.
Gauge The thickness of steel sheet or wire diameter.
Gauge Pressure A pressure greater than atmospheric pressure
Gel A deformable particle that can pass through a filter
Giardia Cyst A waterborne parasite which causes problems with the digestive system
Graded Density A filter media that is comprised of more open pore sizes on the outside and tighter pore sizes near the core
Gravimetric Efficiency Weight of contaminent as determined by suspended solids analysis.
Head The end closure of a filter housing which may contain ports; or the measurement of pressure in a column of water.
Housing A vessel which has various ports and is configured to direct the flow through a filter cartridge.
Hydrophilic A strong affinity for water
Hydrophobic Lacking an affinity for water
Hydrostatic Test A test to confirm the integrity of a filter pressure vessel or housing. The common test is to pressurize the vessel to 1 1/2 times the design pressure rating.
Immiscible Incapable of being mixed or blended together.
Influent The fluid which enters a filter.
In-line Filter A filter housing whose inlet, filter element and outlet are on a single axis.
Ion A charged atom or molecule.
Ion Exchange A chemical process whereby ions are removed from solution on to an insoluble polymer and replaced by preferred ions.
Laminar Flow A fluid flow which is devoid of any turbulance
Maximum Differential
The Max Delta P of a system at which it can safely operate. 
Mean Filtration Rating The average size of the pores in a filter septum
Media (Medium) The functional portion in a filter element that separates the solids
Media Migration Materials of construction of the filter sloughing into the filtration stream
Membrane An angstrom's thick membrane on a substrate with a controlled number of pores.
Membrane Area The total surface of a membrane usually expressed in square feet or square meters.
Mesh The number of strands in a linear inch of woven filter fabric.
Microfiltration (MF) A filter septum that is designed to remove particles that are 0.1 to 3 microns on size.
Micron A metric measurement equivalent to 10-6 meters.  One inch is equivalent to 25,400 microns.
Micron Rating The measurement of the effectiveness of a given element. 
Mist Small particle liquid dispersion often caused by condensation
Mixed Bed An ion exchange resin bed which has a stoichiometric amount of cation and anion resins.
Module A membrane element with it housing.
Molecular Weight The sum of the atomic weights of the atoms which comprise a molecule.
Molecular Weight Cutoff
Molecular weight value where 90 percent of the feed stream solutes greater than the MWCO will be rejected.
Molecule The smallest particles of pure chemical substances that still retain their composition and chemical properties.
Multi-pass Process A filtration stream which repeatedly passes through a filter medium, as in a closed loop.
Multi-pass Test A destructive test which is used to determine the Beta ratio of a filter medium.
Multifilament The number of continuous strands that are twisted together to form a yarn.
Nanofiltration (NF) A crossflow filtration process which removes solids whose molecular weight is in the 250 to 1000 molecular weight range.
Nephelometric Turbidity
Units (NTU)
The units of the test that incorporates use of light scattering to determine the turbidity of the water
Nominal Rating The arbitrary micron removal rating assigned by the filter manufacturer.
Nonwoven The random ordered fibers held together by a binder to make a filter paper or cloth
Normal Flow Flow that is perpendicular to the filter medium as opposed to tangential.
Osmosis The flow of water from a less concentrated solution to a more concentrated solution through a semipermiable membrane.
Ouside-In Flow The typical flow of a fluid perpendicular to the axis of a filter cartridge.
Ozonator A device which generates ozone by passing a high voltage through air or oxygen.
Ozone (O3) An unstable form of oxygen that is used for oxidizing and sanitizing.
Particle Filtration (PF) A filter medium which removes particles in the 1 to 75 micron range.
Particle Removal
The removal of particles as a function of size as determined by counting individual particles.
Particulate Pieces of solid that are individual and minute.
PED 97/23/EC Pressure Equipment Directives - European Commonwealth directives on the design and fabrication of pressure vessels.
Permeability Membrane flux divided by the average trans-membrane pressure.
Permeate (Filtrate) The filtered stream leaving a membrane filtration system.
Permeator The thousands of hollow fibers which comprise the makeup of a hollow fiber element.
pH The negative log of the Hydrogen ion concentration used to indicate acidity or basisity.
Polymer A large molecular mass comprised of repeating structural units or monomers.
Pore An opening in a filter septum.
Porosity A measurement of the open or porous portion of a filter septum
ppb part per billion
ppm part per million
Precipitate A insoluble solid that is the result of a chemical reaction.
Pressure Drop
(See Differential Pressure)
The difference in pressure between two points.
psi Pounds per square inch
psid Delta pounds per square inch
psig Pounds per square inch, gauge
Pyrogen A molecule or particle which can produce a fever in mammals.
Reagent Grade Water (ASTM) Standards for water prepared by the ASTM depending on the intended use of the water.
Recirculation The continuous flow of a fluid either across a membrane, or through a system.
Recovery (R) Ratio of permeate mass to feed mass, usually expressed as a percentage.
Regeneration Replacement of the ions removed from the process water or stream
Rejection (g) A measure of how well a membrane system retrains or allows passage of a solute.
Resins Ion Exchange resin polymer beads with functional groups to exchange ions.
Resistivity The ability of a fluid to resist the flow of electricity.  An indication of purity in water.
Reverse Osmosis (RO) Overcoming the natural osmotic pressure to make water flow from the more concentrated solution to the less concentrated solution.
Saturation For a given temperature and pressure, it is the concentration of solute that will no longer be soluble in the solvent.
Scaling The build up of salts, primarily hardness, on the walls of pipes, and tanks.
SCFM Standard Cubic Feet per minute
Screen Another term for a filter septum
Semipermeable A membrane property that permits solvent to pass through but not all the solute.
Septum/Septa A filter surface
Side Seal The closure of the filter media that is parallel to the axis of the filter element.
Silt Density Index (SDI) A test which indicates the amount of suspended solids in a feed water
Single Open End (SOE) A filter element in which the flow passes through the filter and out one end; the other end being closed.
Single Pass Process A process in which the fluid passes through the media only once.
Solutes That which is dissolved in a solvent
Sparger A device which introduces a gas into a liquid to mix the liquid or dissolve the gas in the liquid.
Specific Gravity The ratio of the mass of a solid or liquid to the mass of an equal volume of water.
Stage One or more membrane modules sharing the same circulation pump.
Strainer A filter element or medium which has a pore size of greater than 40 microns.
Surface Media Very thin filter media that provide a very high flow rate.
Suspended Solids Solid material which is held in suspension in a solvent
Thixotropic Flow Fluids which show a time dependant change in viscosity when shear stress is applied
Throughput The total volume of a fluid that is processed by a filter before the filter is replaced.
Total Dissolved Solids (TDS) The total amount of solids dissolved in a solvent
Total Organic Carbon
The total amount of carbon compounds in a water sample
Total Solids (TS) The total amount of solids both dissolved and suspended in a solvent
Total Suspended Solids (TSS) The total amount of solids that a not dissolved in a solvent
Trans-Membrane Pressure (TMP) The pressure differential driving permeate through a membrane.
Turbidity The cloudiness in a solvent that is caused by suspended solids that will not settle.
Turbidity Units The units of measure of the ability of a light beam to be transmitted through a fluid.
Turbidimetric Efficiency The percentage reduction of the haze in a fluid.
Turbulent Flow Flow at which laminar flow is exceeded
Ultrafiltration (UF) Cross flow semipermiable membrane separation of particles from 10 Angstroms to 0.2 micron.
Ultraviolet (UV) Radiation which has a wavelenght that is shorter than visible light but longer than soft X-rays.
Uniform Density Having the same weight per unit volume of a septum from its influent to effluent ends.
Unloading The release of previously removed contaminants from a filter by an increase in pressure.
United States Pharmacopoeia (USP) The manual of standards for the pharmaceutical industry established by the US Congress.
Validation In the pharmaceutical industry it is the process and record keeping necessary to prove compliance.
Velocity The amount of free air passing through a filter panel.
Vessel A device which is designed to hold filter elements or bags.
Viscosity The resistance to flow demonstrated by some fluids
Void In a filter septum, it is the openings or pores.
Volatile Organic
Compound (VOC)
An organic compound which will develop a vapor pressure from solution.
Volume Reduction Factor (VRF) Ratio of feed volume to concentrate volume.
Water For Injection (WFI) Water which meets the standard of the USP for medical injection and irrigation.
Water Hammer Pressure variations caused by quick acting valves on a non-compressible fluid.
Water Point Permeability when operating the system on clean water at standard reference conditions.
Common Conversions
14.5 psig = 1 Bar = 1.02 kg/cm2 = 0.1 MPa
1 meter = 3.28 feet
1 gfd = 1.7 lmh
1 m3/hr = 4.4 gpm
1 US gallon = 3.785 liters
1 horsepower = 0.746 Kw
1 psi = 2.31 feet of water column
1 ppm = 1 mg/liter
1 m3 = 1000 liters = 1 metric ton


© Graver Technologies, 2008.