Glossary of Terms

Glossary of Terms


Absolute Rating

Micron size of a particle that will be removed by a filter at the stated efficiency


The movement of a liquid or gas into the pores of a solid.


A liquid or gas being held on the surface of a solid


Actual Cubic feet per minute


Fabrication standards of American Society of Mechanical Engineers


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


The dispersion of solid or liquid particles in air that will stay dispersed for a period of time


The aggregation of smaller particles into a larger one


The ability to neutralize acids. Usual pH is between 7 and 14.


An atomic particle with a negative charge


Any compound that kills or inhibits micro-organisms on contact


A unit of measure of pressure



Flow through a filter in the reverse direction


A large variety of single celled micro-organisims that lack a nucleus.


A device which is used in filter housings to divert the incoming stream to provide uniform flow


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


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.


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


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 integrity 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.


A fluid flowing through a passage other than through the filter media



The surface accumulation of solids on a filter medium.

Cartridge Filter

A cylindrical element, usually disposable, which is inserted into a filter housing.


An atomic particle with a positive charge

Caustic Soda

A trade name for Sodium Hydroxide, NaOH.


A fibrous, vegetable material used as a filter medium


Cubic Feet Per Minute

Chelating Agent

A soluble, organic molecule which will hold metal ions in solution


A chlorine/ammonia compound which demonstrates greater persistence than chlorine alone.


The addition of small amounts of chorine gas to water to disinfect the water.

CIP (Clean-In-Place)

The chemical cleaning applied to a fouled membrane to restore it to its original flux performance.


Filtration of fluids containing a small amounts of particles.


The separation or arrangement of particles by size.

Collapse Pressure

Pressure which is great enough to collapse a filter.


Submicron particles held in suspension in fluid and will not settle out


The degree of change in volume when subjected to pressure.

Concentrate (Retentate)

The non-filtered stream leaving a membrane filtration system.


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.


Vapor which has coalesced into a liquid state.


The ability of a liquid to conduct an electrical current.  The inverse of resistivity.

Contact Time

The time it takes an absorbent to be in contact with a liquid to remove a contaminant.


Particles in a fluid which are undesirable.

Cross-Flow Filtration

A mode of filtration in which the pressurized feed stream flows parallel to the membrane surface.


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.


Mass per unit volume.

Depth Media

Filtration media which removes particles within the media as opposed to the surface.

Diatomaceous Earth (DE)

A naturally occurring 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 (Jmax)

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.


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.


Under given conditions of contaminant and concentration, it is the percent ability to remove the contaminant.


The name of the stream as it exits a treatment system.


A suspension of small liquid droplets within a second liquid that will not mix.


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.


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.


United States Environmental Protection Agency.


In filtration, these are compound that leach into the filtrate.


United States Food and Drug Administration.


The input fluid to a treatment process.


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.


A fluid which has been through a filter medium.


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).


A deposition of retained solids on a membrane surface or in the pore structure of the membrane.


A test which measures the air permeability of a filter septum.

Free Water

Refers to captured water in a separation system.  Usually a coalescer.


The thickness of steel sheet or wire diameter.

Gauge Pressure

A pressure greater than atmospheric pressure.


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 contaminant as determined by suspended solids analysis.


The end closure of a filter housing which may contain ports; or the measurement of pressure in a column of water.


A vessel which has various ports and is configured to direct the flow through a filter cartridge.


A strong affinity for water.


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.


Incapable of being mixed or blended together.


The fluid which enters a filter.

In-Line Filter

A filter housing whose inlet, filter element and outlet are on a single axis.


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 turbulence.

Maximum Differential Pressure

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.


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.


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.


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.


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.


A membrane element with it housing.

Molecular Weight

The sum of the atomic weights of the atoms which comprise a molecule.

Molecular Weight Cutoff (MWCO)

Molecular weight value where 90 percent of the feed stream solutes greater than the MWCO will be rejected.


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.


The number of continuous strands that are twisted together to form a yarn.

Nano Filtration (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.


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.


The flow of water from a less concentrated solution to a more concentrated solution through a semipermiable membrane.

Outside-In Flow

The typical flow of a fluid perpendicular to the axis of a filter cartridge.


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 Efficiency

The removal of particles as a function of size as determined by counting individual particles.


Pieces of solid that are individual and minute.

PED 2014/68/EU

Pressure Equipment Directives - European Commonwealth directives on the design and fabrication of pressure vessels.


Membrane flux divided by the average trans-membrane pressure.

Permeate (Filtrate)

The filtered stream leaving a membrane filtration system.


The thousands of hollow fibers which comprise the makeup of a hollow fiber element.


The negative log of the Hydrogen ion concentration used to indicate acidity or basicity.


A large molecular mass comprised of repeating structural units or monomers.


A measurement of the open or porous portion of a filter septum.


part per billion.


part per million.


A insoluble solid that is the result of a chemical reaction.

Pressure Drop (See Differential Pressure)

The difference in pressure between two points.


Pounds per square inch.


Delta pounds per square inch.


Pounds per square inch, gauge.


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.


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.


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.


Ion Exchange resin polymer beads with functional groups to exchange ions.


The ability of a fluid to resist the flow of electricity.  An indication of purity in water.

Reverse Osmosis

Overcoming the natural osmotic pressure to make water flow from the more concentrated solution to the less concentrated solution.


For a given temperature and pressure, it is the concentration of solute that will no longer be soluble in the solvent.


The build up of salts, primarily hardness, on the walls of pipes, and tanks.


Standard Cubic Feet per minute.


Another term for a filter septum.


A membrane property that permits solvent to pass through but not all the solute.


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.


That which is dissolved in a solvent.


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.


One or more membrane modules sharing the same circulation pump.


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.


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 (TOC)

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.


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 semipermeable membrane separation of particles from 10 Angstroms to 0.2 micron.


Radiation which has a wavelength 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.


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.


In the pharmaceutical industry it is the process and record keeping necessary to prove compliance.


The amount of free air passing through a filter panel.


A device which is designed to hold filter elements or bags.


The resistance to flow demonstrated by some fluids.


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

View commonly used conversions use throught the Graver Technologies catalog.

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