Filtration Glossary

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

ACFM (Actual Cubic Feet Per Minute)

A flow rate measurement corrected to actual operating conditions

Adsorption

Contaminants adhering to the surface of the filter media

Aeration

The introduction of air into liquids, which can degrade fuel or cause foaming

Air Eliminator

Device that removes trapped air or gas from liquid systems

API (American Petroluem Institute)

Industry group that sets fuel, oil, and filtration standards

API Gravity

A measure of petroleum product density compared to water

ASME (American Society of Mechanical Engineers)

Organization that publishes pressure vessel and filtration vessel standards

ASTM (American Society for Testing and Materials)

Standards organization for materials, fuel, and filtration testing

Back Pressure

Resistance to flow occurring at some point in a downstream section of an air or liquid circuit. In liquid systems, this can result from hydrostatic pressure, or in beverage filtration, it can help maintain CO₂ solubility

Backwashing 

The process of reversing flow — using air, steam, or liquid — through a filter medium to clean it by dislodging and removing trapped solids

Baffle

A component inside a filter housing that forces the fluid to change direction, aiding the removal of particulates and liquids via impact. Also used to shield filter elements from excessive flow velocity

Barren Liquor

A liquid used in washing filter cakes that contains little to no recoverable or valuable material

Base Support

The porous foundational layer or structure that supports the filter medium during operation

Basket

A cylindrical or rectangular insert within a basket strainer, typically equipped with a screen, designed to capture larger solids from a liquid or gas flow

Basket Strainer

A type of filter housing containing a screen-lined basket to remove coarse solids from liquid, air, or gas streams

Batch

A defined quantity of material processed or produced in one operation, often used in batch-processing industries like chemicals or coatings

Bay House

An air filtration unit specifically designed to remove airborne particulates

Beta

A filtration performance ratio calculated by dividing the number of particles entering a filter by the number exiting. Used to quantify filter efficiency

Beta Factors

A system of numerical values used to represent the efficiency of a filter trapping particles of specific sizes

Blind Spots

Areas within the filter medium where fluid flow – and therefore filtration – does not occurr

Blinding

Retained particles clog the pores of a filter medium, reducing flow capacity and requiring cleaning or replacement

Blowback 

The reverse flow of air, steam, or liquid through a filter medium to clean it by removing built-up particulates (also referred to as backwash)

Blowdown

The controlled release of accumulated liquids or solids from a filter housing, typically using pressure

Body

The main housing or vessel that contains the filter medium and supports filtration processes

Boil Point

The gas pressure at which bubbles appear in a wetted filter medium under test conditions – measured after the initial bubble point

Breaking Strength

The average tensile force needed to rupture a test sample of filter media or housing material

Breakthrough

The event when contaminants pass through a filter cake, indicating the end of its effective filtration life

Bridging

The formation of a layer or arch of particles across filter openings, restricting flow and sometimes leading to premature blinding

BTU (British Thermal Unit)

A unit of measurement for heat engery; represents the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit

Bubble Point

The pressure at which a gas begins to flow through a wetted filter medium, indicating the largest pore size present

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

Bypass Indicator

Indicator which signals alternate flow

Bypass Valve

Valve to pass the flow around the media or the housing, usually activated at a given differential pressure setting

Cake

A buildup of solids collected on the filter medium during operation, thick enough to be removed in sheet form or chunks. In some systems, this layer contributes additional filtration by acting as an extension of the medium itself. Also called residue or discharged solids

Cake Release

The ability of the filter medium to allow easy detachment of the filter cake after filtration

Cake Repuddling

The process of intentionally breaking up the structure of a filter cake for redistribution or reformation

Calibrating Tank

A tank used to verify volumetric accuracy of liquid delivery systems, such as positive displacement meters

Canister

A container or frame used to house filter elements, sometimes forming part of the element structure or used purely for positioning 

Cap, Element

A component placed at one end of a filter element, securing it inside the housing. Sometimes referred to as a yoke

Cap, End

The end plate of many filter cartridges, particularly those with pleated paper designs, where the media is bonded to form a complete cartridge

Capacity

The total volume a housing can hold or process, often specified in gallons or flow rate per minute at at given efficiency

Capillary

A tiny, narrow tube with a very small internal diameter

Carrying Body

Liquid in which the solid particles are suspended

Cartridge

Medium used in a housing for separation, filtration, or coalescence. Also known as an element or media pack

Catalyst

A substance that accelerates a chemical reaction without itself taking part in the reaction

Caustic

A category of highly reactive chemicals, such as caustic soda or sodium hydroxide

Cellulose

A key organic component of plant fibers, used in filter media for its strength and filtration properties. Filter-grade cellulose is chemically treated to control pore size, improve wet strength, and reduce water wetting

Center Core

The structural support within a filter cartridge that helps maintain its shape. 

Center Pipe

A perforated support rod used to mount filter cartridges and direct flow through them

Center Rod

A solid rod used to mount cartridges inside a filter housing

Center Seal

A sealing component placed between stacked filter elements to ensure separation and proper flow

Center Tube

The internal tube that supports the filter media in the smallest diameter section of the cartridge

Central Procurement

A purchasing system where one office manages buying filter equipment for multiple locations or branches (common in government contracts)

Channel

The formation of grooves or pathway through solids or media that allow unfiltered flow, often resulting in bypass

Chemical Polarity

A measure of how the asymmetric arrangement of atoms in a molecule affects its chemical reactivity

Clarification

The process of removing fine suspended solids from a liquid to improve clarity

Clarity

A qualitative measure of how free a liquid is from visible contaminants

Classification

The natural or intentional separation of particles into layers or size groups, also called stratification 

Clay

A blend of natural clays like attapulgus and montmorillonite used in certain filter elements

Clayslip

Clay in a fluid state – either a sludge or a suspension

Clean Pressure Drop

The differential pressure measured across a filter housing when operating with clean product and new filter elements

Clean Room

A controlled environment designed to minimize airborne contaminants, often used for assembling sensitive equipment

Cloth

A woven fabric, either synthetic or natural, used as filter media

Coagulant

A substance that induces suspended particles to clump together into larger, more filterable masses (flocs)

Coagulation

The process where fine particles in a liquid combine into larger flocs, facilitating easier filtration

Coalescer

A device that combines small droplets of an immiscible phase (like water in oil) into larger drops, making them easier to separate via gravity

Coalescing

The action of merging tiny droplets into larger ones to aid separation

Code

A formal design standard applied to a filter housing (such as ASME Section VIII for pressure vessels)

Colloid

Extremely small particles – solid or liquid – that remain suspended in a surrounding liquid without settling

Color Bodies

Colored deposits or impurities, often hydrocarbons, found in fuels and oils

Compatibility

The ability of different materials to be used together without negative interactions – crucial when selecting filter media for certain fluids

Composite Media

Filter media constructed from two or more different materials to achieve desired filtration characteristics

Compressibility 

How much filter cake particles deform under pressure – important when selecting filter media and gaskets

Concentrate

The fluid entering the filter system, typically containing suspended solids

Condensation

The cooling of a vapor to below its boiling point, converting it back into liquid form

Conditioning

Modifying feed fluid to improve its filtration characteristics 

Consistency

Describes the thickness or fluidity of a liquid product. Thicker liquids are of heavier consistency

Contact Time

The length of time which a fluid is in contact with an absorbent prior to filtration 

Contaminate

Any foreign substance – solid, liquid, or dissolved – in a fluid that negatively impacts equipment or processes

Continuous Phase

Basic product flowing through a filter or filter separator which continues on through a system after being subjected to solids and/or other liquid separation

Conversion

Changing the type of elements in a housing to vary the efficiency

Conversion Kit

A set of components required to adapt a filter housing to accept a different type of element

Convolutions

Multiple pleats or folds in filter media, increasing surface area

Coolant

A fluid used to absorb and carry away heat from a process

Corrosion

The degradation of metal caused by chemical reactions with air, water, or contaminants

Corrugations

Fine ridges or dimples added to filter paper to improve structural integrity and mantain pleat separation

Crenelated

Indented or notched

Critical Operating Pressure 

The maximum pressure at which a filter or separator can operate effectively without performance loss or damage

Critical State

A unique set of conditions (pressure, temperature, composition) where liquid and vapor phases become indistinguishable

Critical Temperature

The temperature above which a gas cannot be converted to a liquid, regardless of pressure

Cycle

A complete operating period for a filtration system, measured in time (hours, days)

D.E.

Short for diatomaceous earth – a naturally occurring, porous mineral used in filtration

Dead Areas

Regions in a filter medium where no filtration takes place. Also known as blind spots

Dead Hand

A gauge feature that records the maximum differential pressure reached between calibration intervals

Dead Void Volume

Void space in the system that does not contribute to liquid flow

Deformable

Describes the particles that can deform and penetrate filter cakes, leading to rapid clogging

Degradation

A decline in filter performance or condition due to wear or other factors

Degree of Filtration

Measurement of fluid cleanliness, typically expressed as milligrams of contaminant per unit volume

Dehydration

The process of removing water (or vaporized hydrocarbons) from a gas or liquid stream, often improving dew point

Delivery

Outlet through which filtered product exits – such as discharge port

Delta (ΔP)

The symbol representing pressure differential across a filter

Density

Mass per unit volume of a substance, often expressed in grams per cubic centimeter or pounds per cubic foot

Depth Filter Medium

Filter media that captures particles throughout its thickness via a maze of small pathways, rather than only on the surface

Depth Type Filtration

Filtration achieved by forcing fluid through a deep medium with complex flow paths, suitable for handling deformable or fine particles

Desalination

The process of producing fresh water by removing salts from seawater or brackish water through methods like reverse osmosis or distillation

Desiccant

A material that adsorbs moisture from air, gas, or liquids – examples include silica gel and molecular sieves

Detergent Oils

Special lubricants with dispersants that prevent sludge buildup in internal combustion engines

Dewater

To remove water from solid material

Dew Point

Temperature at which air or gas is saturated with moisture, causing condensation

Diaphragm

A flexible component in valves that allows movement while maintaining internal pressure

Diatomaceous Earth

A fine, porous material made from fossilized algae often used as a filter precoat

Diesel Fuel

A petroleum-based fuel used in diesel engines

Differential Pressure

The pressure difference between two poitns in a system, often measured across a filter

Differential Pressure Indicator

A device that displays or signals the pressure difference across a filter

Differential Pressure Switch

An electrical switch that activates based on pressure difference – commonly used to trigger filter maintenance alerts

Differential Rating

The maximum pressure differential a filter element can tolerate without failure

Diffusion

In filter cake washing, the movement of wash liquid through the cake to displace trapped original liquid

Digested Sludge

Organic-rich sludge that has been decomposed by bacteria

Dimensional Stability

A material’s ability to maintain its original size and shape during use

Direct Reading Differential Pressure Gauge

A gauge that directly displays the pressure drop between two points

Direction of Flow 

The intended flow path of a fluid through a filter element

Dirt Holding Capacity 

The amount of contaminant a filter can retain before reaching its maximum allowed pressure drop – often measured in weight 

Disc Pack Element

A type of filter element constructed from stacked discs of filter media 

Discharge 

The liquid or gas that exits a filter housing after passing through the medium 

Discharge Liquor

Liquid output from filtration, often called filtrate, product, or effluent

Discharge Valve

Valve controlloing flow from the outlet of a filter housing

Discharge Solids

Accumulated solids thick enough to be removed in sheets or chunks – also known as filter cake

Discontinuous Phase

The phase being separated from the main (continuous) phase – for example, water droplets removed from oil

Discrete

Describes distinct, separate particles – commonly used for describing discontinuous phases

Dispersion

The process by which solid or liquid particles become suspended in a fluid. Also applies to two-phase systems, where one phase (the dispersed phase) is distributed throughout another (the continuous phase)

Disposable

An element designed to be used once and discarded, then replaced with an identical unit. Same as replaceable. Opposite of reusable

Dissolved Solids

Any solid material that dissolves in the liquid being filtered – for example, sugar dissolved in water

Distillate

The condensed liquid product obtained through distillation, such as certain petroleum fractions

Distillation

A method of separating liquids by vaporizing them and collecting the vapor, which is typically condensed back into liquid form. Since pure substances boil at specific temperatures, one liquid can often be separated from another based on boiling point – although this becomes difficult when substances have similar boiling points

Divider

A metal plate component inside a housing used to form separate chambers, such as inlet and outlet sections

Downstream

The portion of a system or product flow that has already passed through filtration equipment such as a filter or separator

Drain Valve

A valve used to release material that has been separated from a fluid stream. May also refer to a diaphragm-operated valve that automatically removes the discontinuous phase

Drop

A small spherical mass of fluid; also may refer to multiple droplets grouped together

Droplet

A very small liquid particle, which can combine with others to form larger drops that are heavy enough to fall by gravity

Dual Gravity Valve

A float-operated valve that functions at the interface of two immiscible liquids with different densities, releasing one liquid phase

Duplex Filter

An assembly of two filters with valving to select one or both filters for operation

Dynamic Adsorption

An adsorption process where there is continuous motion between the fluid being treated and the adsorbent – often achieved by passing the gas or liquid through a stationary bed of adsorbent. 

Dyne

A unit of force that causes a one-gram mass to accelerate by one centimeter per second for each second the force is applied

Effective Area

The portion of the filter medium that is exposed to flow and actively used for its intended function – coalescing, filtering, or separating. Opposite of dead zones or blind spots

Efficiency

The capability of an element to remove solids and/or liquids from a stream

Efficiency Curve

A performance graph showing how a filter behaves when exposed to specific contaminants (natural or artificial) under controlled test conditions. The plot typically shows penetration or efficiency versus particle size at a constant face velocity 

Effluent

The fluid stream exiting a filter or separator – the opposite of affluent or influent

Element

A filter medium housed in a system to perform coalescing, filtering, or separating. Also called a cartridge, repack, or media pack

Element Cap

A component covering one end of the filter element, holding it securely in place within the housing

Elongation

Stretch or deformation of a material caused by tensile force, measured as a percentage of its original length 

Elutration

The process of washing out suspended solids from sludge 

Emissions

Gases and/or particulate matter released into the environment, usually the atmosphere

Emulsification

The dispersion of one material into another in the form of fine droplets

Emulsion

A mixture where fine liquid droplets are dispersed in another liquid. The liquids may not disssolve into each other but remain suspended.

Emulsion Separation

The chemical process used to separate emulsions, typically by removing oil from spent cutting oils before disposal – often using chemical dosing with metal salts. Other techniques may involve heat, electricity, or physical separation. 

Encapsulated

Describes a material coated or enclosed in a plastic film or outer layer

End Caps

Componenets attached to each end of a filter element (using adhesive or other means) to hold the medium in its designed form.

End Load Rating

The maximum axial load of a filter element can withstand without permanent deformation or compromising the seal 

End Point

The final target in a process. In petroleum distillation, the temperature where distillation stops. In filtraiton, this may refer to a pressure level where further use of the element is not recommended, or a color change signaling the end of chemical activity

End Seal

The bond between the filter medium and its end cap – often created with adhesives such as epoxies or polyurethanes in pleated paper cartridges. Also refers to the seal between the cartridge and housing

Entrained Water

Tiny water droplets carried within a continuous liquid or gas stream – especially when the water is immiscible with the main phase. These droplets can be separated using coalescing and gravity

Entrainment

Mist, fog, or fine droplets of liquid that are typically considered contaminants in filtration processes 

Equalizing Line

A connection used to balance pressure or vacuum between two different system points

Equillibrium Loading

The maximum loading a filter medium can support under defined temperature, pressure, and concentration conditions. Also used to describe an even distribution of particles on a filter surface

Eutectic

A mixture with the lowest possible melting point for its components – melting completely at a single temperature into a uniform liquid

Extended Area

A product line of pleated celluslose filter cartridges designed with increased surface area for higher flow rates, greater efficiency, and larger solids-holiding capacity. Manufactured with controlled specifications for pore size, weight, and strength – available in various grades for a wide range of applications

Federal Stock Number

An identification number assigned by the U.S. Government to classify specific items in their inventory. The number is typically preceded by the letters FSN

Feed

The material being filtered. Also known as concentrate, influent, intake, liquor, mud, prefilt, pulp, slime, or sludge

Felt

A fabric formed by interlocking fibers using a combination of mechanical action, chemical treatment, moisture, and heat. Often used as a filter medium, with some types suited for high-temperature air or gas filtration

Fiber

The basic unit of textile materials – examples include cotton, wool, and synthetic fibers

Fiber Migration

The movement of fibers from the filter media (coalescer, separator, or cartridge) into the effluent stream. A more specific term than media migration, as fiber migration refers to identifiable fibers

Fiberglass

A general term for products made with or composed of glass fibers

Film Strength

The ability of a lubricant to resist rupture or breakdown when placed under pressure between two metal surfaces

Filter

A device used to remove solid contaminants from liquids or gases. In modern usage, the term “filter” generally applies to equipment removing solids only. Systems that remove both solids and liquids are better described as separators or filter separators. “Filter” is sometimes incorrectly used to describe the medium itself, which should be properly called an element or cartridge

Filter Coalescer

A single-stage horizontal housing used to coalesce and separate immiscible fluids and remove solids. Recommended for systems where the continuous phase has a light density

Filter Medium

The porous material that traps solids during filtration. Often mounted on a frame or plate, and also known as filter cloth, filter plate, or septum

Filter Monitor

A water-absorbing filter element designed to continuously remove dirt and water from aviation fuel

Filter Paper

A permeable web made of randomly oriented fibers (usually cellulose or glass fibers), created on a paper-making machine. The permeability is determined by fiber type and preparation. Resin-treated filter papers offer wet strength, and creped papers provide increased surface area. Used to remove particulates from liquids or gases

Filter Plate

A porous material mounted on a plate or frame to separate solids from liquids. Also called filter cloth, filter medium, or septum

Filter Separator

A housing that removes both solids and entrained liquids from another liquid or gas stream. It typically combines baffles, coalescers, filter elements, or separator elements in single or two-stage configurations, sometimes with a prefilter for bulk solids

Filter System

A complete filtration setup, including the filter and all supporting hardware needed for operation

Filterability

The relative ease (or difficulty) with which a fluid can be filtered

Filters, Bulk Type

Similar to depth filters but without graded density, resulting in variable filtration reproductibility 

Filters, Inert Type

Filters designed to remove insoluble contaminants. Generally applies to filters other than those using adsorbent or adsorbent media

Filters, Surface Type

Typically constructed with pleated, impregnated paper or combinations of paper and glass fibers. Opposite of depth-type filters

Filtrate

The liquid that passes through the filter, separated from solids. Also known as discharge liquor, effluent, mother liquor, solute, or strong liquor

Filtration

The process of separating solids from liquids or gases by passing them through a porous medium 

Filtration Beta Ratio

The ratio of particles larger than a specified size (n) in the incoming fluid to the number of particles larger than size (n) in the filtered output

Filtration Rate

The amount of liquid that passes through a filter over time, usually expressed in gallons per square foot per minute (or hour)

Fines

The fraction of a powder made up of particles smaller than a specified size

Fire Point

The lowest temperature at which a liquid emits vapor rapidly enough to sustain continuous combustion – typically close to the flash point

Flash Distillation

A process where liquid vaporizes instantly upon entering the system

Flash Point

The lowest temperature at which a flammable liquid emits enough vapor to ignite momentarily

Float Control

A float-actuated pilot valve that controls other valves or orifices, often used to remove a discontinuous phase at the interface of two immiscible liquids – or to control liquid level in air/gas systems

Floating Scraper

A balanced scraper that follows the contour of a rotating drum with minimal pressure

Flocculation

The process of small particles agglomerating into larger clumps (flocs), making them easier to filter. Also known as coagulation

Flow

Describes how fluid moves through a system. Viscous (laminar) flow is controlled by fluid viscosity, while turbulent flow is influenced by inertia. Laminar flow typically occurs at Reynolds numbers below 2,000 turbulent flow above 4,000

Flow Rate

The volume of product moving through a system, expressed in units such as gallons per minute (GPM), barrels per hour (BPH), cubic feet per minute (CFM), etc.

Flow Resistance

The pressure required to force a unit volume of fluid through the filter medium. See also resistance ventilation filter

Fluid

In filtration terminology, this term includes liquids, gases, and air

Fog

Condensed water, hydrocarbons, or other visible liquid droplets suspended in air

Fractionation Tower

A vertical vessel where rising vapors meet descending liquids, allowing for separation based on boiling points – lighter fractions move upward, heavier ones remain below

Frazier Permeometer

A device used to measure fabric porosity – typically by gauging airflow (CFM) through one square foot of material at a fixed pressure differential. Tighter fabrics measure 2-10 CFM, while very porous ones can reach 450-500 CFM

Free Board

The clear space between the surface of the liquid and the top edge of the filter housing

Freezing Point

The temperature at which a liquid and its solid phase are in equilibrium – the liquid will solidify below this point and melt above it. Freezing point depends on liquid composition

Friable

Easily crushed or broken apart

Friction

The resistance that arises when one surface moves across another – can be reduced by introducing a lubricant, shifting from solid to fluid friction

Fuel Monitor

A housing that monitors fluid cleanliness and shuts off flow when contamination (solids or water) reaches a critical level. Moisture-sensitive elements trigger pressure changes to activate the shutoff

Fuel Wettable

Capable of being wetted by fuel. Opposite of non-wettable

Full Flow

The entire process of flow passing through the housing and filter medium. The opposite of a bypass system, where only a portion of the flow is filtered continuously at higher efficiency

Fuse

See filter monitor

Gas

A state of matter where molecules move freely, causing the substance to expand indefinitely to fill the available space. Some definitions reference critical temperature – the temperature above which gas cannot be liquefied by pressure alone

Gas Scrubber

A housing designed to remove liquid and solid contaminants from gas streams by forcing impingement on baffles or demister pads. This is achieved by greatly reducing gas velocity as it enters the scrubber. In broader use, mechanical cartridge-type separators may also be considered gas scrubbers

Gaseous Stream

A fluid stream that contains gas, either alone or mixed with a liquid

Gasket

A sealing material placed between contact surfaces in a joint to ensure a leak-proof seal. It is typically softer than the surfaces it contacts but should not permanently bond to them. Gasket material selection depends on temperature, pressure, and the chemical properties of the fluid being contained

Gelatinous

Describes suspended solids that are slimy, deformable, and prone to quickly plugging filter media

Glass Fiber

Fibrous material made from glass, used in filter and separator media. It may be used in blanket or tubular form. The random fiber distribution provides excellent filtration characteristics. These fibers are hydrophilic (water wettable), making them effective for coalescing immiscible liquids. Glass fiber can be used with compressed air, gas, or certain liquids, including mildly acidic ones. Also known as fiberglass

Glycol

A general term for a family of alcohol-based compounds – clear, colorless, and varying in solubility in water, alcohol, ether, benzene, etc. Common uses include coolants, antifreeze, and in various processing applications

GPD

Gallons per day

GPH

Gallons per hour

GPM

Gallons per minute

Gravity

The ratio between the weight of a material and an equal volume of water. In the U.S., this is commonly expressed in terms of API gravity or specific gravity

Gravity Filter

A type of filter where the driving force is the liquid’s own head height – no added pressure or vacuum is used. Gravity filters are often chosen for compressible materials or flakes that would otherwise clog under high differential pressure

Gravity Separation

The process of separating immiscible phases based on differences in specific gravity, typically aided by coalescence 

Grease Filter

A filter assembly that may include both coalescing and adsorptive sections. The coalescing section is often made from knitted wire or glass fiber, while the adsorptive section typically uses activated carbon

Grooved Coupling

A clamp device with tongue-like edges that fit into corresponding grooves to create a sealed connection. Commonly referred to by the trade name “Victaulic”

Gross Solids

A term used to describe an unusually heavy solids load in a system

Gross Water

A term describing an abnormally high water content in a stream

GSFM

Gallons per square foot per minute – a flow rate measurement. Also seen as GSFH (gallons per square foot per hour)

Haze

A fine suspension of smoke or dust that affects visibility. In liquids – especially beverages like wine – a fine suspended materials causing an opalescent appearance is also called haze

Head Gasket

The sealing gasket used at the main closure of a pressure housing – typically located between two flanges. Common types include flat gaskets or o-rings

Head Lift

A mechanism used to raise the head of a vertical pressure housing, allowing access to the housing interior

Heat of Adsorption

The heat released when a substance is adsorbed onto a surface – equal to the energy the adsorbed material must give up when moving from its normal state to the lower energy adsorbed state. The exact heat varies with the adsorbate and adsorbent used

Heat of Vaporization

The amount of heat energy required to convert a liquid into vapor at its boiling point

Holding Capacity

The total amount of solids, particulates, or foreign material that one or more filter elements can retain before reaching terminal or maximum differential pressure. Can also refer to the volume capacity for holding either solids or liquids

Homogeneity

A measure of uniformity – describing even particle size and distribution in a solid product

Hydrocarbon

One of many chemical compounds made primarily of hydrogen and carbon. Depending on molecular weight and boiling point, hydrocarbons can exist as gases, liquids, or solids.

Hydrophilic

Describes a surface or substance that readily adsorbs or interacts with water (water-wettable). A hydrophilic medium is necessary for efficient coalescing, as it helps entrained water form droplets that can combine and separate via gravity. Opposite of hydrophobic

Hydrophobic

A surface or material that resists interaction with water (non-water wetting). Hydrophobic properties can be introduced during celluslose manufacturing. Opposite of hydrophilic

Hydrostatic Test

A pressure test performed with air, water, or other fluids at a level above the housing’s design pressure – used to verify structural integrity

ID

Inside diameter

IFT

Interfacial Tension

IMHOFF Tank

A tank used for settling sewage and digesting sludge – it features an upper sedimentation chamber with a sloped floor that channels solids into a digestion chamber below

Immiscible 

Incapable of mixing or dissolving into one another; opposite of miscible

Impingement

A process that removes liquid or solid contaminants from a compressed air or gas stream by directing flow at high velocity onto a baffle plate. The contaminants fall into a calm sump area, preventing re-entrainment. The method can also be applied to liquid streams to separate solids

Inert

Inactive chemically or physically

Influent

Stream of fluid at the inlet of a filter or filter separator. Same as affluent. Opposite of effluent

Inhibitor

A chemical or material that slows or prevents undesirable reactions, such as corrosion, oxidation, or polymerization. Some inhibitors alter interfacial tension in petroleum products, which may reduce coalescing efficiency by creating tighter emulsions

Initial Pressure Drop

The differential pressure observed when new elements begin operation in a housing

In-Line

Describes processes – such as mixing or conditioning – that occur directly within the pipeline, eliminating the need for separate tanks or mixing vessels

In-Line Filter

A filter or strainer that operates as part of a continuous flow system within the piping

Insoluble

Unable to dissolve in a fluid. Opposite of soluble

Intake

The material entering the filtration process. Also called concentrate, feed, influent, liquor, mud, prefilt, pulp, slimes, or sludge

Interchangeable

An element that can replace another in the same application, provided dimensions match. The substitute element often offers enhanced features

Interface

The boundary surface where two immiscible phases – continuous and discontinuous – come into contact

Interfacial Tension

A measurement of how miscible or soluble two liquid phases are. A higher value indicated lower miscibility

Interpleat

Combining two or more types of filter media, such as glass fibers and cellulose, into a single pleated element

Interstices

The small spaces or voids within a medium, often in adsorptive materials like carbon 

Interstitial

Related to the spaces or pores within a medium

Ion

An atom or group of atoms with an electrical charge, formed by gaining or losing electrons

Ion Exchange

A reversible chemical process – typically between a solid and a liquid – in which ions are swapped between the two phases

I.P.

Abbreviation for the Institute of Petroluem

Isokinetic Sampling

A method where fluid is sampled through a probe at the same velocity as the free stream. Essential for accurately capturing solid or liquid particles larger than 5 microns in gas streams

Isotherm

A line or curve representing constant temperature

Isotropic

Having identical properties in all directions

Jet Fuel

A petroleum-based product used to power jet engines

JFTOT

Abbreviation for jet fuel thermal oxidation tester – a standard test method used in the aviation industry to measure jet fuel’s tendency to form deposits when exposed to high temperatures

Kerosene

A petroleum-derived liquid commonly used as fuel or for heating applications

Kieselguhr

A finely ground siliceous material, similar to diatomaceous earth but typically containing more impurities

Knife Edge Pleat

Sharply defined creases formed along the outer cage of a pleated filter element

Knife Edge Seal

A narrow, pointed ridge on a sealing surface – such as an end cap, center seal, or cartridge adaptor – that creates a seal by embedding into the cartridge gasket

L-Type Filter

A cartridge filter in which the inlet and outlet ports are positioned at right angles, while the filter element’s axis runs parallel to one or both port axes

Lacquer

A natural or synthetic resin dissolved in an appropriate solvent – typically an aromatic-rich hydrocarbon oil. Upon application, the solvent evaporates, leaving behind a lacquer film 

Laminar Flow

Also known as streamline flow or viscous flow. A flow regime where the characteristics are primarily influenced by the fluid’s viscosity

Leaf

A flat filter element that either contains or supports the filter septum

Life Expectancy

The anticipated operational life of a filter element before replacement is required – this varies based on the element’s design, operating conditions, and the quality of the influent

Line Size

The nominal size of piping used to transport product within a system – for example, a six inch line 

Liquid

Refers to the process stream being filtered. In gas-liquid separation, may also refer to the liquid phase to be removed by an entrainment separator

Liquid Level Control

Typically a float-operated device that functions at the interface between two liquid phases, used to remove one liquid from a housing after separation. In gas service, it controls liquid removal from the gas stream

Liquor

The material entering a filtration system – also called concentrate, feed, influent, intake, mud, prefilt, pulp, slimes, or sludge

Liter

Equal to 1.057 quarts. A volumetric standard used to measure liquids, especially for determining water or solids content

Lock Up

A mechanism that secures a column, elements, or the housing body in place

Low Interfacial Tension

Refers to situations where the interfacial tension between two liquids is below 5 dynes/cm at 70°F. See inhibitor for its effect on coalescing performance

LOX Cleaning

A specialized cleaning process for components used in liquid oxygen service – removes hydrocarbons and other foreign materials to ensure compatibility

Lubrication

The process of introducing a lubricating fluid between two moving surfaces to replace solid friction with fluid friction

LVM (Low Volatile Material)

Substances that have a low tendency to evaporate or vaporize at a given temperature and pressure

Main Closure

The access point through which a filter housing is serviced, used when the housing has more than one opening 

Male Mounting Cap

A device that allows filter elements to be mounted through an opening in a tube sheet. Typically removed with the cartridge. Often used in conversion kits

Manifold

A pipe or assembly that connects multiple filter elements, providing a common outlet for the filtered product

Mass

The amount of matter contained within a body, regardless of location

Mass Distribution

The distribution of particle sizes by mass, often presented as a cumulative percent undersize

Mass Transfer

The movement of matter from one point to another

Mass Transfer Rate

A measurement of the rate at which mass moves, often expressed in terms of atoms or molecules over time

Matter

The material substance of which elements or masses are composed. In this context, not referring to cartridge elements

Maximum Allowable Pressure Drop

The highest differential pressure a housing is rated to handle under specified product and flow conditions

Maximum Differential Pressure

The maximum pressure difference a filter element can withstand without structural damage or collapse

Maximum Operating Pressure

The highest pressure allowed in the system

Mean Efficiency Rating

The average efficiency of a filter medium, determined by Multi-Pass testing. Corresponds to an average BETA ratio of 2.0

Media

The material that performs the separation of solids from liquids or gases. Sometimes mistakenly called a septum

Media Migration

The carryover of media materials (such as fibers) from filter or separator elements into the effluent. More general than fiber migration

Medium

The core material within a filter element – either a controlled-pore structure that removes particles or droplets, or an uncontrolled material (like glass fiber mat) that aids in filtration or separation

Membrane

A medium through which liquids are passed for separation – commonly used in ion exchange, dialysis, osmosis, and diffusion. Filter paper could also be classified as a membrane

Membrane Filter

A thin, permeable polymer film with controlled pore size, number, and shape. Used in bacterial filtration, sterilization, beverage processing, and ultrapure water systems. Available as cylindrical cartridges for applications such as reverse osmosis and dialysis

Mesh (Wire Cloth)

The number of openings per linear inch in wire cloth. May also be expressed as a fractional movement. Should not be confused with clear opening or space between wires

Meter Proving Tank

A tank used to verify volumetric accuracy of positive displacement meters. Also called a calibrating tank

Micrometer

One millionth of a meter – a standard SI unit of length

Micron

A unity of length equal to one millionth of a meter. Used to describe filter performance, the size of particles being removed, and the condition of influent or effluent. Typically expressed as absolute or nominal rating – nominal generally means 98% removal of particles above the rated size

Microorganisms

Living organisms that can only be seen with a microscope

Microscope Count

A method of estimating mean particle size by using a microscope with calibrated aids. Requires 500-600 observations for accurate results

Migration

The release of contaminants downstream of a filter. Categories include built-in dirt migration (introduced during manufacturing), contaminant migration (caused by unloading), and media migration (due to materials from the filter media itself)

Milliliter

One-thousandth of a liter – equivalent to approximately one cubic meter

Miscible

Capable of being dissolved or mixed into another substance. Opposite of immiscible

Mist

Visible droplets of water or hydrocarbon vapor suspended in air or gas

Mixing

The process of intermingling fibers from similar sources to create a uniform blend. Distinct from blending, which typically involves different fiber types, colors, and materials

MMSCFD

Million standard cubic feet per day

MMSCFH

Million standard cubic feet per hour

MMSCFM

Million standard cubic feet per minute

Mole

A quantity in chemistry representing the amount of a substance equal to the sum of the atomic weights of all atoms in a molecule. Expressed as a gram mole or pound mole

Molecular Sieve

A natural or synthetic zeolite with a lattice structure containing numerous small cavities and precisely sized pores. Used for drying gases or liquids and in other adsorption processes. Can be regenerated under specified conditions

Molecular Weight

The sum of atomic weights of all atoms in a molecule. Sometimes called mol weight or mole weight

Monofilament

A single, continuous synthetic fiber strand

Montejus

A closed pressure tank partially filled with fluid, forced out by applying gas pressure to its surface

Montmorillonite

A soft mineral commonly found in bentonite clay – forms a mud-like texture when wet but does not significantly expand

Mother Liquor 

The liquid that passes through a filter. Also called discharge liquor, effluent, filtrate, solute, or strong liquor

Motivating Force

The driving force behind coalescing, filtering, or separating actions

MS

Military Standard – prefix used for government-assigned item numbers built to military specifications

MSCFD

Thousand standard cubic feet per day

MSCFH

Thousand standard cubic feet per hour

MSCFM

Thousand standard cubic feet per minute

Mud

Material entering a filtration system. Also called concentrate, feed, influent, intake, liquor, prefilt, or sludge

Mud Sump

A section in a horizontal housing (before the media) where solids settle by gravity before reaching the coalescing media – used when large amounts of solids are present

Mullen Burst Test

A measurement of the force needed to burst a specific area of paper or cloth under fluid conditions. Usually stated as the pressure (inches of water) required to burst a 1-inch diameter specimen

Multifilament

A yarn formed by twisting together multiple continuous fiber strands – used in weaving filter cloth

Multi-Pass

A test method simulating hydraulic or lubrication circuits. Contaminants are added to the test fluid and circulated repeatedly through the test filter

Multiple Cartridges

Two or more filter cartridges fastened together end-to-end to form a single element

Negative Pressure

A condition of vacuum or suction

Nominal

An industry term used to define a degree of filtration. Filtration manufacturers may use varying definitions, making ratings non-standard. Typically, nominal means 98% removal of particles larger than the stated micron size on a single pass. See also: absolute

Nominal Rating

An approximate micron value assigned by the manufacturer. Because of inconsistencies between methods, this rating is considered deprecated

Nonaqueous

Not related to, carried by, or containing water

Nonpolar

A molecule or element whose electrons are fully satisfied, leaving it electrically neutral and typically non-reactive. Opposite of polar

Nontoxic

Non-poisonous; having no toxic effect

Nonwoven

A filter cloth or paper that is formed of synthetic fibers that are randomly oriented in the media. Typically held together with a binder

Normal Piling

The structural formation of a filter cake during operation

Nozzles

Inlet and outlet ports on a filter housing through which fluid flows; may also refer to accessory connection points. The term “nozzle” is not considered as descriptive 

NPT

National Pipe Thread standard

NTP

Normal temperature and pressure – typically defined as gas at 1 atmosphere absolute (760mm Hg) and 0°C. Some definitions use a different reference temperature 

Occluded

Absorbed within a material

OD

Outside Diameter

On-Stream

Describes when a filter system is actively producing filtered product 

Open Area

The pore space in a filter medium – often expressed as a percentage of total surface area

Operating Pressure

The normal working pressure of system during operation 

Operating Pressure, Critical

A pressure above design or normal limits that may lead to equipment damage

Operating Pressure, Maximum

Maximum pressure allowed in the system

Organic

Describes the vast number of chemical substances containing carbon, hydrogen, and oxygen

Organic Solvents

Liquids capable of dissolving organic material

Orifice Plate

A flat plate with a central circular opening, installed in piping or ductwork. Pressure tappings on or near the plate allow measurement of the pressure drop across the plate, from which flow rate can be calculated

Osmosis

The diffusion of a solvent through a semi-permeable membrane from a dilute solution toward a more concentrated solution, aiming to equalize concentration on both sides of the membrane

Out of Balance Pressure

The unequal pressure on opposite sides of a filter press plate, which may result from blocked feed ports or inconsistent conditions in adjacent chambers

Outer Shell

The external covering of a filter element – often perforated or screened

Outer Wrap

An outer protective covering or layer on a filter element

Outlet (Filtrate Outlet)

Ports in a filter plate though which filtrate exits the filter chamber 

Outside-In

A flow direction where product flows from the outside to the inside of the filter element

Oxide

A chemical compound consisting of oxygen combined with another element

Oxidation

A chemical reaction where an element’s oxidation state (positive valence) increases

Ozone

A a gas that appears deep blue when compressed. Though unstable and potentially explosive under pressure, it is used as ozonized air produced by electrical discharge. While previously considered beneficial to health, Ozone is now known to be harmful and its presence in air-handling equipment is undesirable

Packed Bed

Discrete materials such as sand, gravel, anthracite, fabricated rings or saddles, assembled in a confined space as a filtration medium liquids or gases

Paper

Filter medium used in many elements – generally refers to resin-impregnated cellulose. A wide range of cellulose papers are engineered to specific requirements for filtration

Particle

Single piece of solid material which is small in relation to its environment. Normally characterized by its size and shape

Particle Count

The process of grouping and counting solid particles by size. Commonly used to design filters for specific applications or to evaluate filter performance under defined conditions

Particle Size Distribution

A data set showing particle size groupings (usually by micron size) within an influent or effluent stream. Results are typically expressed as a percentage of total solids in each group (e.g. % in the 6-10 micron range). See particle count

Particulate

Relating to minute, separate particles

Pellet Strength

The ability of a pellet to resist breaking or producing dust during service

Perforated

Describes material (such as a center tube) that has been punched with holes

Perlites

Naturally occurring volcanic glass-like material with a concentric shell structure

Permeability

The ability of a cake or filter medium to allow liquid to pass through. Lower permeability generally indicates better retention of fine particles

Permeable

A material with openings that allow liquid to pass through during filtration. Also known as porous or pervious

Pervious

See permeable

pH Range

A scale from 0 to 14 used to indicate the acidity or alkalinity of a solution. pH 7 is neutral; values below 7 are acidic; above 7 are alkaline

Phase

May refer to either the continuous phase (product flowing through a housing) or the discontinuous phase (the material being separated)

Phenolic Resins

Synthetic thermosetting resins derived from the reaction of phenols with aldehydes – used as binders in cellulose and glass fiber filter media

Pigment

Natural or synthetic chemical substances (organic or inorganic) used for coloring paints, inks, and other products

Plastisol

A thermosetting plastic in suspension that can be molded. Often used as an element’s end cap or gasket material

Plate

Flat-surfaced filter element – commonly used in horizontal plate filters

Pleat, Pinched

A pleat in a filter element that has been compressed by excess differential pressure, reducing effective filtration area

Pleat, Spacers

Supports that prevent pleats from collapsing under pressure – may include expanded metal, plastic, or wire-cloth

Pleated

Describes a filter cartridge that has been folded accordion-style to increase surface area

Pleating

The folding process used to create pleats in filter media, increasing surface area within a given volume

Plugging

Occurs when trapped particles fill filter pores, restricting or stopping flow. Also called blinding or blocking

Polar

A molecule or element capable of gaining or losing electrons

Polyelectrolyte

Synthetic, water-soluble polymers with ionizing groups – used to aid flocculation

Polymerization

A chemical process in which small molecules (monomers) bond to form large molecules (polymers)

Polyurethanes

Synthetic plastics formed from reactions between di-isocyanates and dihydric alcohols, polyesters, or polyethers

Pores

Openings in a filter medium. Also called interstices

Pore Size Distribution

The distribution of pore sizes in permeable media, often compared to particle size distribution

Porosity

The ratio of a medium’s void volume to its total volume. Higher porosity generally means larger or more pores

Porous

A material with openings that allow liquids to pass – also known as permeable or pervious

Potable

Safe for drinking

Pour Point

The lowest temperature at which a liquid will flow under specified conditions

PPM

Parts per million – a unit of concentration

Precoating

Applying a layer of inert filter aid to a filter surface before starting filtration

Prefilt

The material entering a filtration system. Also called concentrate, feed, influent, intake, liquor, mud, pulp, slimes, or sludge

Prefilter

A filter used to remove large contaminants before product enters the main filter separator

Prefilter Coalescer

A two-stage horizontal housing designed for high-rate removal of solids and water from light gravity streams

Prefilter Coalescer Separator

A three-stage housing used when streams contain high solids. The first stage removes bulk solids to improve coalescing and separating in the later stages

Pressure Absolute

A three-stage housing used when streams contain high solids. The first stage removes bulk solids to improve coalescing and separating in the later stages

Pressure, Atmospheric

Atmospheric force at sea level – equivalent to 14.7 psi

Pressure, Expressed in Atmospheres

Gauge pressure divided by 14.7 – expressed in atmospheres

Pressure, Partial

In a gas mixture, the pressure of each gas equals the total pressure times its mole (volume) fraction. The sum of all partial pressures equals the total pressure

Pressure, Proof

A test pressure above normal operating limits to verify that equipment will not fail

Pressure Differential

The difference in pressure between two points

Pressure Drop

The pressure difference (drop) across a filter or filter separator – typically measured between inlet and outlet

Pressure Drop, Clean

The differential pressure across a new, clean filter at rated flow

Pressure Drop, Maximum Allowable

The highest pressure differential allowed for a housing at specified product and flow conditions

Pressure Relief

A valve that prevents excess pressure buildup by releasing fluid from a housing

Pretreatment

Physical or chemical methods used to improve the filterability of a liquid-solid mixture. Techniques include coagulation, flocculation, sizing, aeration, agitation, freezing, heating, ultrasonic or mechanical vibration, electrical or magnetic treatment, and the use of filter aids 

Prime

Refers to either a government prime contractor, the first coat of paint, supplying a pump with liquid for startup 

Product

The continuous phase (liquid, air, or gas) being processed in filtration or separation equipment

Prover Tank

A tank used to verify the volumetric accuracy of positive displacement meters. Also called meter calibrating tank or meter proving tank

PSI

Pounds per square inch

PSIA

Pounds per square inch absolute

PSID

Pounds per square inch differential

PSIG

Pounds per square inch gauge

Pulp

Material to be filtered – also called concentrate, feed, influent, intake, liquor, mud, prefilt, slimes, or sludge. In papermaking, also refers to fiber material used to make paper and cellulose products

Pulsating Blowback

Intermittent bursts of air or gas used to dislodge filter cake, with or without actual discharge of the cake

Purification

The removal of water or hydrocarbon vapor from an air or gas stream – lowering the stream’s dew point. Related to dehydration, clarification, or classification

Quiescent

A state of rest or inactivity. In entrainment separation, this typically refers to the liquid phase. The term also describes a sump where separated liquids or solids collect undisturbed

Rate of Flow

See flow rate

Rate of Flow Control

Valve operated by differential pressure across an orifice for control of the rate at which a product flows through a housing

Rated Flow

Normal operating flow rate at which a product is passed through a housing; flow rate which a housing and medium are designed to accommodate

Raw Sludge

Untreated sewage sludge

Recycle

Return of filtered liquid for another filtering; a continuous flow of liquid through an open or closed system

Red Mud

Filter cake in sodium aluminate filtration

Redistill

To distill a liquid again

Reentrainment

The process by which previously captured particles become airborne again – for example, from increased airflow velocity or mechanical vibration of a filter

Regenerated

Cleaned of impurities and restored for reuse

Regenerated Cellulose

Cellulose-based fibers that have been physically – but not chemically – altered. Includes viscose, cuprammonium, and nitrocellulose rayons

Rejects

Undesired material remaining after ore disintegration

Relative Humidity

The ratio (as a percentage) of the actual water vapor present in air at a given temperature to the maximum amount the air can hold at that temperature

Repack

A cylindrical element used in single-stage filter separators for removing water and coarse solids from another liquid. May be used individually, in combinations, or in clusters. Typical media include excelsior, glass fibers, or steel wool

Repair Kit

A collection of frequency replaced parts for an accessory – intended to allow complete service of high-wear components

Repellency

The ability to repel water (hydrophobic behavior); opposite of water wettable

Replaceable

A filter element intended to be discarded after use and replaced with an identical one. Synonymous with disposable. Opposite of reusable

Residue

Solids left behind on the filter medium after filtration – often thick enough to be removed as sheets or larger pieces. Also called cake or discharged solids

Resin Impregnated

Describes fiber that has been treated with resin to enhance strength and durability. Resin is carefully controlled during manufacture to maintain desired filter properties

Resin-Wool

Filter media composed of wool combined with resin – used for particle removal from gas streams. Common in industrial respirators

Resistance

In ventilation filters, the pressure drop across a filter at a stated flow rate – typically expressed in mm water gauge or Pascals. See also flow resistance

Retainer

A device used to hold a filter component in place

Retention

The ability of a filter medium to capture and hold particles of a given size

Retrofit

A modification that converts a filter or separator to a new configuration or functionality

Retrofitting

The process of modifying existing equipment to add improvements or new features

Reusable

A filter element that can be cleaned and reused. Opposite of disposable or replaceable

Reverse Osmosis

A membrane-based process that separates solvent from a solution. High pressure is used to overcome natural osmotic pressure and force solvent through the membrane, retaining solutes. The purified solvent is called permeate. See osmosis

Reynolds Number

A dimensionless number (LVP/N) used in fluid dynamics to describe flow condition

RFSO

Raised Face Slip-On – a type of flange facing

RFWN

Raised Face Weld Neck – a type of flange facing

RTJ

Ring Type Joint – a type of flange facing, which may be used on slip-on, weld neck, or long weld neck flanges

Runs

Refers to filtration cycles or batches

SAE Number

Viscosity classification for crankcase and transmission lubricating oils, standardized by the Society of Automotive Engineers

Sand Filter

A filter composed of layered sand, graded so that coarser material faces incoming flow. Common in water filtration. Variations using crushed coke or grit have also been used for gas filtration

Scavenger

An element or filter at the bottom of a tank that recovers remaining liquid at the end of a cycle

SCFD

Standard cubic feet per day

SCFH

Standard cubic feet per hour

SCFM

Standard cubic feet per minute 

Screen

A protective covering for a filter element, or the core material of separator elements or baskets. May have special coatings like Teflon®

Screw Base

A threaded element base that mounts by screwing onto a cartridge adaptor

Seal

Any component used to prevent leakage – includes gaskets, O-rings, center seals, mounting caps, and machined surfaces (metal-to-metal seals)

Seal Nut

A gasketed nut that secures an element cap

Sedimentation

The settling of suspended solids

Selector Valve

A pressure gauge component that allows readings from multiple points 

Self-Cleaning

A filter that clears itself via blowdown or backwash – often used for bulk solids removal at high flow rates

Separation

The process of removing solids or liquids from a fluid. Achieved by impingement, filtration, or coalescing

Septum

A permeable support material for filter media

Service Life

Length of time a filter element can operate before it reaches the maximum allowable pressure drop

Serviced

A housing that has had old elements replaced. May also include gasket replacement, cleaning, and accessory repairs

Shell

The outer wall of a housing – also called body or housing

Silica Gel

A regenerated amorphous silica adsorbent used for drying or dehumidifying gases, liquids, and oils

Silting Index

A measure of a fluid’s tendency to cause silting in close-tolerance devices due to to fine or gelatinous

Single-Pass

Test method where contaminant is added to fluid and passed through a test filter. Remaining contaminant is removed by a cleanup filter before fluid is recirculated

Single-Stage Filter Separators

Filter separators with only one type of replaceable element (unlike two-, three-, or four-stage separators)

Size Distribution

Proportion of particles by size (by mass, number, or volume) in a powder or suspension

Skid-Mounted

A portable unit with one or more housings plus pump and motor mounted on a frame

Slag

Waste byproduct from blast furnaces or coal burning

Slimes

Fine solids slurry – material to be filtered

Sludge

Residues and deposits – often from extended oil use; also material to be filtered

Slug Valve

A pilot-operated valve that stops flow when a slug liquid (like water) passes through. Also called discharge valve

Slurry

A watery suspension of solids – material to be filtered

Smog

A fog containing industrial pollution or fine particles and gases

Smoke

Particles smaller than 5 microns, formed by condensation, oxidation, or other processes

Soft Iron Filled

Gasket filled with small soft iron particles

Solids

Undesirable mass or matter in a fluid stream – removed through filtration

Soluble

Able to dissolve in a fluid. Opposite of insoluble

Solute

The liquid that has passed through a filter – also called filtrate, mother liquor, or effluent

Solution

A single-phase mixture of a solvent and dissolved substances

Solvent

A liquid that dissolves another substance – typically the larger component in a solution 

Sonoco

Trade name for a kraft-impregnated paperboard center tube

Sp. G.

Specific Gravity – weight of a substance relative to water

Space

Available area for installing a filter or separator

Spectrophotometer

Instrument measuring the wavelength and intensity of light emitted by chemical elements – used for trace analysis

Spin-On Filter

An integral disposable filter that screws onto a filter head for quick replacement

Spinning

A manufacturing method for shaping pressure housing heads

Spore Forming Bacteria

Bacteria capable of forming resistant resting cells

Squatty

A short-profile filter or meter proving tank

SS

Stainless steel (type & material unspecified)

Stack

Multiple cartridges mounted on a single column

Static Generation

Static electricity created by friction between non-conductors (e.g., filter elements and hydrocarbons)

Steel Jacketed Asbestos

Gasket material with a steel outer layer

Stock

Refers to paper pulp feed or a specific oil in refining

Stool

Mounting device for filter elements – also called cartridge adaptor

Stratification

Larger particles settling below finer ones. Also called classification

Stream

Refers to a product, liquid, or other matter processed through filtration

Substrate

A material on which an enzyme acts, or a base material used to make filter media

Sump

A collection area in a housing for separated liquids or solids. Also called water leg or mud sump

Supernatant

Liquid remaining above settled solids

Surface

Part of filter medium perpendicular to flow – in surface filtration

Surface Energy

Molecular forces causing iron release from a surface

Surface Filter

A filter that traps particles entirely on its surface

Surface Tension

A liquid’s tendency to minimize surface area due to cohesion

Surface Tensity

The quality or condition of a liquid’s surface

Surfactants

Surface-active agents (wetting agents/emulsifiers) that lower interfacial tension and may interfere with coalescing

Surge

A peak in system pressure caused by flow restriction

Suspended Solids 

Undissolved solids present in a liquid – removable by filtration 

Suspension

A liquid containing undissolved solids

Swing Bolt

A quick-opening housing closure. Faster than thru-bolt designs

Temperature, Absolute

Temperature measured from absolute zero (-273°C or −460°F).

Tensiometer

An instrument for measuring surface tension of a liquid, or interfacial tension between two immiscible liquids

Terminal Pressure

The pressure drop across a filter system at shutdown or when maximum allowable pressure drop has been reached

Terminal Velocity

The constant velocity a particle achieves when falling through a fluid – when gravitational force is balanced by viscous drag

Thermal Relief

A valve preset to open when pressure rises due to increased temperature

Thermoswitch

A temperature-sensitive control used to start and stop an immersion heater at preset temperatures

Three-Stage Filter Separators

Liquid prefilter coalescer separators with three types of replaceable elements. For air/gas applications, includes two types of elements plus a first-stage baffle. Compared to single-stage, two-stage, or four-stage separators

Thru-Bolt

A housing closure using studs and nuts (such as ASA flanges)

Titration

A method of analyzing a solution by adding a second solution until a specific reaction occurs

Tortuous Path

A winding or irregular path that helps trap solid particles 

Toxic

Poisonous; having harmful effects

Tramp Oil

Free oil in emulsion-type coolants – may result from machine leakage or emulsifier breakdown. Can impair filter performance and is often removed by belt or drum skinners

Transmission

The percentage of contaminant that passes through a filter or filter medium. Synonymous with penetration or transmittance

True Density

The mass of a particle divided by its volume, excluding internal pores. See porosity 

Tube

Refers to center tube, mounting tube, or a wound or molded cylindrical cartridge (such as glass fiber) 

Tube Sheet

A cartridge mounting plate

Turbidity

Cloudiness or opacity in a liquid caused by suspended insoluble particles

Turbulent Flow

A flow regime dominated by fluid inertia rather than viscosity – associated with high Reynolds Numbers and greater drag forces

Two Stage Filter Separator

A liquid or air/gas filter separator using two types of replaceable elements (or one plus a baffle in air/gas). Considered highly efficient for separating immiscible liquids – compared to single, three, or four stage separators

Ultrafiltration

The process of separating colloidal solids from liquids using a semi-permeable medium

Uniformity Coefficient

A sizing factor for sand used in water filtration plants – calculated as the ratio of the mesh size through which 60% of the sand passes to the mesh size through which 10% passes. Common sand size is 0.4 to 0.6 mm with a uniformity coefficient not exceeding 1.7 

Uniformity of Feed

Refers to the even distribution of solids within the feed liquid 

Unloading

The release of previously trapped contaminants downstream – can result from flow changes, vibration, mechanical stock, excessive pressure, or media failure

Upstream

The portion of the product stream that has not yet passed through the filtration system

Vacuum

A space devoid of matter – a true void. Often used to describe pressures below atmospheric, created by partial air removal. Many filters operate under vacuum below the filter cloth, using atmospheric pressure above to create differential pressure

Vapor

A gaseous state of a solid or liquid under normal temperature and pressure. More generally, a gas below its critical temperature. See critical state and critical temperature

Vegetable Fiber

A paper-like material used for gaskets

Velocity

The rate of motion in a given direction over time

Velocity Head

Kinetic pressure – equal to half the product of fluid density and the square of its velocity. It represents the difference between total and static pressure in incompressible flow

Viscosity

A fluid’s resistance to flow – a result of its molecular cohesion and adhesion. Measured in poise or stokes. A liquid that has 1 poise viscosity if a force of 1 dyne/cm² moves two surfaces 1 cm apart past each other at 1 cm/sec. Many test methods exist, generally measuring flow time of a fluid or movement of an object through the fluid

Viscosity Index (VI)

A number that indicated how much a lubricating oil’s viscosity changes with temperature – higher VI means less change

Viton A

Trade name for a gasket and O-ring material

Void Channels

Open pathways in a medium through which fluid travels

Void Restriction

Blockages in void spaces that interfere with fluid flow

Voids

Open spaces in a medium – also called interstices or pores

Volumetric Flow Rate

The amount of fluid volume flowing per unit time (e.g., cc/sec, ft³/min) 

Wafer

Type of repack consisting of four or more cylindrical

Waste

Material that is removed, rejected, or lost during manufacturing process

Water Leg

The section of a housing designed to collect water – see also sump 

Water Wettable

Able to accept water – hydrophilic in nature. Opposite of hydrophobic or repellent surfaces

Weight of Solids

The amount of solid particulate matter in a fluid sample – typically reported as mg/L, weight percent, lbs per barrel, etc.

Wet Strength

The strength of filter medium when saturated with water. May also refer to filter paper treated with additives to improve strength when wet

Wetted

Condition of a material that has absorbed or been covered by water or another liquid

Yoke

End cap used to hold a cartridge in place

Zeolite, Artificial

Desiccant made in various-sized pellets