Glossary of Oil Filtration Terms
This glossary defines oil filtration terms used in the filter industry and explains how these terms are applied. Filter Industry is a general term intended to include such products as filters, coalescer/separators, prefilters, clay treaters, etc. Because this list contains many words that may be considered colloquial or expressions coined by equipment manufacturers, it may also be viewed as a vocabulary of filter terms. While many of these terms may have other definitions in other industries or engineering usages, the definitions used herein are limited to the use or application as they relate to the filtration industry.
ABRASION – Migration of foreign material which enters the fluid stream from system components that wear from close tolerances, vibration, or shock.
ABRASIVE WEAR – Wear caused by abrasive particles
ABSOLUTE – An arbitrary term used to describe or define a degree of filtration. The filtration industry uses various methods of determining absolute ratings that are not necessarily interchangeable. Generally, absolute references 100% removal of solids above a specified micron rating on a single pass basis.
ABSOLUTE FILTER – In liquid filtration, absolute implies the size above which no particles will be found in the filtrate, e.g., a one‑micron absolute filter. It has been applied to air filters of high efficiency, greater than 95% against submicron particles, but is now less frequently used. Modern terminology prefers HEPA filter (High Efficiency Particulate Air), but a better form is probably HESPA (High Efficiency Submicron Particulate Air).
ABSOLUTE RATING – The diameter of the largest hard, spherical particle that will pass through a filter under specified test conditions. This is an indication of the largest opening in the filter element.
ABSORB – To soak in, as a sponge soaks in water.
ACTIVATED CARBON – Carbon activated by high temperature to form a material of high adsorptive capacity.
ACID – A large class of compounds that contain the element hydrogen (H+) in its formula, which may be replaced by metallic salts. The deleterious effect most acids may have on filter medium and housings is of primary concern. An acid is capable of neutralizing or being neutralized by a base.
ACIDITY – The quality, state, or degree of being acid. In lubricating oils, acidity denotes the presence of constituents whose concentration is usually defined in terms of a neutralization number. The constituents vary in nature and may or may not markedly influence the behavior of the fluid.
ACTIVATED ALUMINA – A highly porous and granular form of aluminum oxide having preferential adsorptive capacity for moisture from gases, vapors, and some liquids. It may be regenerated for extended use under specified conditions.
ACTIVATED CARBON – Any form of carbon characterized by high adsorptive capacity for gases, vapors, or colloidal solids. The carbon or charcoal is produced by destructive distillation of wood, peat, lignite, nut shells, bones, vegetable or other carbonaceous matter, but must be activated by high temperature steam or carbon dioxide which creates a porous particle structure.
ACTIVATED CHARCOAL – Reference Activated Carbon.
ACTIVATED CLAY – An adsorbent clay that removes color, odor, tree fatty acids, surfactants, etc., from oils and hydrocarbons.
ACTIVATED SLUDGE – Biologically active floc from aeration and settling sewage and/or organic matter.
ACTUATION PRESSURE – The preselected PSID setting of a differential pressure indicator at which the final button actuates.
ADDITIVE – A material, usually chemical, added to a product to impart new or unusual characteristics or to improve existing characteristics.
ADHESION – Intermolecular forces that hold matter together. Also applied to the sticking together of a particle to a surface, a fiber, or another particle. The main factors affecting the adhesion of particles are (1) London‑van der Waals forces, which are electrical in origin, (2) electrostatic forces, and (3) surface tension due to films of moisture on particles or on the surface. Other factors influencing adhesion are the
nature of the surfaces, surface contaminants, particle size, shape and roughness, and time of contact.
ADHESIVES – Used in the essential bonding process between cylinders of pleated filter paper and end caps in paper filter element production. Types used include air drying synthetic rubber/solvent/resin mixtures, two part epoxide and/or polyurethanes, and heat curing adherent plastisols.
ADHESIVE WEAR – Wear caused by metal-to-metal contact due to oil film breakdown (example scuffing).
ADSORB – Attracting and holding a gas, vapor, or liquid on the surface of a solid.
ADSORBENT – A solid material that adsorbs, such as clay, carbon, or activated alumina.
AEROSOL – A dispersion of small particles in a gas.
AFFLUENT – Fluid entering the filter or filter separator. More commonly described as influent. Opposite of effluent.
AGGREGATE – A fluid mixture of concentrated solids to be filtered.
AGGLOMERATE – A cluster of particles more or less fixed firmly to one another as a sintering or growing together.
AIR ELIMINATOR – Float‑operated valve to evacuate air or gas from a housing or chamber.
ALKALI – A term that applies to the type of compounds that have basic properties and which will neutralize acids. Some alkaline materials are hydroxides, carbonates, caustics, etc.
AMBIENT – The term used to present a generalized description of an environment (ambient temperature). The localized atmospheric environment.
AMORPHOUS – Non‑crystalline, having no determinable form or crystalline form. Solids to be removed by filtration may be amorphous.
ANION – Negatively charged ion, i.e., an atom or molecule that has gained one or more electrons in an electrolyte. It travels to the positive electrode, the anode, on electrophoresis or electrolysis. Anions include all nonmetallic ions, acid radicals, and the hydroxyl ion (OH). (Reference Ion Exchange)
ANTIFORM AGENT – An additive used to suppress the foaming tendency of petroleum products in service. Maybe a silicon oil to break up surface bubbles or a polymer to decrease the number of small entrained bubbles.
ANTIWEAR AGENT – Additives or their reaction products that form thin, tenacious films on highly loaded parts to prevent metal-to-metal contact.
ANHYDROUS – Free from water.
API – American Petroleum Institute
APPARENT DIRT CAPACITY – The actual weight of contaminate injected into the filter test system when the terminal press drop is reached.
AREA – The available apparent surface exposed to the flow of a fluid for maximum utilization. The function of area in filtration is related to initial pressure drop, rate of flow, and solids retention capacity. In many applications, proper utilization of the area of medium produces greater efficiency and solids retention. This is accomplished by pleating the material into an accordion form to create an increased surface area much greater than in a cylindrical form.
ASBESTOS – A group of impure magnesium silicate minerals that are found in fibrous form.
ASH – Inorganic, noncombustible solid residue remaining after combustion. Some additives, particularly conventional detergent additives, leave behind a powdery residue after combustion. Excess ash can cause engine malfunction if allowed to build up in the combustion chamber, cylinder liner ports, and turbochargers.
ASH (SULPHATED) – The ash content of an oil is determined by burning the oil and complexing the metals in the residue with sulphuric acid, expressed as % by mass.
ASME – American Society of Mechanical Engineers. Published code which governs the design of pressure housings.
ASSEMBLY – A general term to describe the combination of a number of items used to make up a whole. Example: A cartridge mounting assembly for a filter would include the cartridges and all items needed to install the assembly in the filter housing. Final assembly would be used to name the action of assembling all items into an end product.
ASPHALTENES – Components of asphalt that are insoluble in petroleum naphtha but are soluble in aromatic solvents. They are made up largely of high molecular weight polynuclear hydrocarbon derivatives containing carbon, hydrogen, sulphur, nitrogen, oxygen, and usually nickel, iron, and vanadium.
ATMOSPHERIC PRESSURE – The pressure of approximately 4.7 pounds per square inch exerted at sea level in all directions by the atmosphere.
ATTRITION – A wear caused by rubbing or friction. It produces fine particles that usually contaminate liquids surrounding the attrition point. Sometimes referred to as scouring or scoring.
BACKWASH – To reverse flow air, steam, or fluid through the filtration medium, resulting in the removal of solids.
BAFFLE – Component of a housing which constitutes a stage when used; removes liquid and solids by impingement; may be either upstream or downstream of the basic filter medium. It may also be a plate to protect filter elements from the velocity of flow entering the vessel.
BAR – A unit of pressure one (1) Bar = 14.5 PSI.
BASE – A compound that reacts with an acid to produce a salt plus water.
BASE NUMBER – A measure of the acid-neutralizing power in a lubricating oil, also known as Total Base Number.
BASE STOCK (BASE OIL) – Refined petroleum oil used to produce lubricants and other products. The base stock may be used alone or blended with other base stocks and/or additives to manufacture a finished lubricant.
BASKET – Element for a basket strainer. A device typically uses a screen as its medium for the removal of coarse bulk solids.
BASKET STRAINER – Housing for removing coarse bulk solids from liquid, air, or gas; the element is a basket covered with a screen of a given mesh.
BETA RATIO – The ratio of the number of particles of a specified micrometer in the influent fluid to the number of particles the same micrometer in the effluent fluid.
BLEED – The extraction from any circuit of a proportion of the throughput for sampling, quality control, recirculation, or process control.
BLIND SPOTS – Places in filter medium where no filtering occurs. These are also referred to as dead areas. Opposite of effective area.
BLINDING – Reducing or shutting off of low due to closing pores in the filter media.
BLOWBACK – To reverse flow air, steam, or fluid through the medium to effect solids removal. Sometimes referred to as backwash.
BLOW-BY – A passage of combustion gases past the piston rings of internal combustion engines, contaminating the crankcase oil.
BLOWDOWN – The action to evacuate liquids and/or solids from a vessel using pressure.
BRIDGING – Where particles being removed form an arch over the individual opening in the filter medium.
BTU (BRITISH THERMAL UNIT) – A standard measure of heat content in a substance that can be burned to provide energy.
BUBBLE POINT – The differential gas pressure, which, when applied to a filter element submerged near the surface of a test fluid, causes the first steady emission of gas bubbles from the filter element. A means of verifying the micron rating.
BUNA N – A nitrile rubber seal compound frequently used for housing closures, flanges, and filter elements.
BURST PRESSURE – The maximum pressure a housing will safely withstand.
BURSTING STRENGTH – The ability of a filter medium, such as a filter paper, to resist disruption by pressure applied in a direction normal to the surface.
BYPASS – Condition resulting from the product flowing through a housing without flowing through the medium. Also, a filtering system continuously filters only part of the stream. Opposite of full flow.
BYPASS INDICATOR – An Indicator that signals alternate flow.
BYPASS OIL FILTRATION – A bypass filter is used to eliminate nearly all contaminants in the engine oil while not starving the engine during the process. It is called bypass filtration because the oil flows from the bypass filter back to the sump and bypasses the engine. This continual process will eventually make all of the oil analytically clean, reducing long-term wear, and can extend drain intervals. Centrifugal bypass filters are the most effective and economical way to remove smaller particles effectively.
BYPASS VALVE (RELIEF VALVE) – Valve to pass the flow around the filter media or the housing, usually activated at a given differential pressure setting.
CAKE – Solids deposited on the filter media.
CAPACITY (DIRT HOLDING CAPACITY) – The quantity of contaminant that a filter element is capable of retaining without exceeding a specified differential pressure at rated flow.
CATALYST FINES – Small (typically less than 50 microns) particles of aluminum silicate used as a catalyst in catalytic cracking (cat cracker) refineries. They are sometimes carried over in the refinery process and can be found in residual fuels. They are very abrasive and can cause excessive wear in engine parts, particularly fuel pumps, injectors, cylinder liners, and piston rings.
CAPILLARY – Fine, hairlike tube having a very small opening.
CARTRIDGE – Medium used in a housing to perform the function of coalescing, filtering, or separating. Also referred to as element, media, repack, etc. It is made in a specified physical shape to be mounted using hardware designed for that purpose.
CASE SHUT-OFF VALVE – An optional design feature of filter assemblies that allows the case and element to be removed without draining the system.
CATION – A particle carrying a positive charge which, in an electrolytic process, moves toward the cathode. It may refer to a positive ion, molecule, or radical. (Reference Ion Exchange)
CATALYST – A substance that accelerates a chemical reaction without itself taking part in the reaction. For example, alkylation will not take place unless some substance such as sulfuric acid is present; such a substance is called a catalyst.
CATALYTIC FINES – Abrasive contaminants resulting from catalytic cracking processes.
CELLULOSE – A fibrous material of vegetable origin.
CELLULOSIC MEDIA – Compact structures of fibers, basically cellulose, impregnated with resin for strength, rigidity, and fluid compatibility.
CENTER TUBE – A support device designed to support the filter medium in a filter element while permitting fluid flow and resisting element collapse.
CENTIPOISE – A unit of absolute viscosity. One (1) centipose equals 0.01 poise.
CENTISTOKE (cSt) – A unit of kinematic viscosity. One (1) centistoke equals 0.01 stoke. 
CENTRIFUGE – A machine designed to subject material held in it or being passed through it to centrifugal force. Separation is achieved due to any difference in density, i.e., accelerated sedimentation.
CENTRIFUGE FILTRATION – The process that uses centrifugal force generated by high-speed spinning to separate solid particles from a liquid medium, essentially accelerating the natural sedimentation process by applying a force much greater than gravity, allowing for rapid separation of components based on their density; it is often used in applications like separating contaminants from lubricating oils or clarifying liquids in industrial settings.
CLARIFICATION – Filtration of liquids containing small quantities of suspended solids; filtration takes out most of these solids and increases the clarity of the liquids.
CLARITY – Amount of contaminates left in a filtered liquid; the absence generally indicates the liquids to be free of contamination to an unspecified degree.
CLAY – A naturally occurring material usually being activated and used as an adsorbent.
CLEANABLE FILTER ELEMENT – A filter element that, upon reaching a predetermined differential pressure, can be cleaned to an acceptable level of performance for reuse in its fluid system.
CLEAN PRESSURE DROP – Differential pressure (drop) across a housing, measured in pounds per square inch at rated flow on new elements with clean product.
CLOTH – A type of woven filter septum made from natural or synthetic yarns.
COAGULANT – That which produces coagulation or agglomeration of suspended solids.
COALESCER – Means of causing the disperse phase of two liquids to combine into discrete droplets which, by reason of a difference in density compared with the continuous phase, will separate. Coalescers/separators are widely used for separating water from petroleum fuels.
COALESCING – Action of uniting of small droplets of one liquid preparatory to its being separated from another liquid.
COLLAPSE PRESSURE – The minimum differential pressure that a filter element is designed to withstand without permanent deformation.
COLLOID – Tiny, insoluble, non‑diffusible solid or liquid particles that remain suspended in a surrounding liquid. Solids are usually on the order of 0. μ or less.
COLLOIDAL PARTICLES – Gelatinous substance of minute particles which remain in suspension.
COMPOSITE MEDIA – Media made up of more than one material.
CONCENTRATE – Material to be filtered; also referred to as feed, influent, intake, liquor, mud, prefilt, pulp, slimes, or sludge.
CONDITIONING – Improving the filtering qualities of the filter feed.
CONTAMINANT – Undesirable solid, liquid, or gaseous material present in the liquid or gaseous medium.
CONTAMINANT CAPACITY – The resultant weight of a contaminant which, when added at specified internals and at a specific flow rate, produces a differential pressure a differential pressure across a filter element which can be converted or related to the useful life of a filter element.
CONTAMINATE – Foreign matter in a fluid which is accumulated from various sources such as system dirt, residue from wear of moving parts, and atmospheric solids which settle in an open system. Contaminates tend to discolor a liquid, cause additional wear on moving parts, cause system upsets in process streams, or reduce fluid efficiency. Water, as well a solid, may be considered a contaminate when the presence of water causes adverse results. The presence of contaminates, whether liquid or solid, is the basis on which the use of filters or filter separators is sought.
CONVOLUTING – The accordion pleating of filter media to obtain a large effective filtration area in a minimum volume.
CORE – Material used for the center of an element, generally of the wound design. It may also be called a center tube when used in the coalescer, separator, or other types of filter elements. It may also be a tube of fibers formed into an element with sufficient strength to provide its own center core.
CORROSION – Conversion of metals into oxides, hydrated oxides, carbonates, or other compounds due to the action of air, water, or both. Salts and sulphur are also important sources of corrosion. Removal of solids and water reduces the effect or speed of corrosion in many cases; in other cases, corrosion inhibitors are used to reduce the effect of corrosion.
CORRUGATIONS – Fine ribbing is sometimes applied to filter paper following resin impregnation and before pleating to form a pleated paper filter element. Corrugations that run at right angles to the main pleats help hold the pleats apart against the differential pressure encountered in use. Discontinuous corrugation or dimples are sometimes alternately employed.
COUNT – Used in the term particle count to tabulate number and sizes of solids in specified groups.
CRITICAL OPERATING PRESSURE – Pressure above which filtration or separation equipment may produce reduced efficiency or fail to function correctly.
CYCLE – Filtration interval; length of time filter operates before cleaning.
CYCLONE – Liquid or gas filter using the principle of centrifugal force, which causes the contaminant to settle to the bottom of the housing without the use of a filter medium.
CYLINDRICAL – Having round sides, the ends being equal circles. Opposite of pleated when used to describe elements.
DEAD AREAS – Places in medium where no filtering occurs. These are also referred to as blind spots. Opposite of effective area.
DEGRADATION – Wearing down, or reduction in the efficiency of medium.
DEGREE OF FILTRATION – A measure of the efficiency of filter element expressed in terms of percentage retention of standard contaminants under defined test conditions (Nominal Rating) and the size in microns of the largest hard spherical particle that will pass through the filter element (Absolute Rating).
DEHYDRATION – Removal of water or hydrocarbon in vapor form from an air or gas; also water from another immiscible liquid. Differs from entrainment removal in that the dew point of a gas stream will be lowered by vapor removal. A form of purification.
DELTA P (ΔP) – Pressure drop, differential pressure.
DENIER – A unit of size of textile thread. The basis is that 450 metres have a standard weight of 0.05 gm of significance in describing filter fabrics.
DENSITY – Compactness or thickness; ratio of medium weight to an equal volume of fiber. In general, mass per unit volume is usually expressed in grams per cubic centimeter, pounds per cubic foot, or gallons.
DEPTH FILTRATION – Filtration accomplished by flowing a fluid through a mass filter medium, providing a tortuous path with many entrapments to stop the contaminates. Flow may be cross flow, such as from the outside to inside and then down the center of an element, or from end to end. Certain types of solids, or combinations of solids, do not lend to surface filtration, where depth-type filtration is found to be more suitable.
DESALINATION – Production of fresh (potable) water from sea water, salt or brackish water by one of several processes, e.g., distillation, flash distillation, electrodialysis or reverse osmosis if salt content is not too high.
DESICCANT – A drying agent or medium used in the dehydration of air, gas, or liquids. Examples: silica gel, activated alumina, molecular sieve, etc.
DETERGENT OILS – Lubricating oils possessing special sludge-dispersing properties for use in internal combustion engines. These properties are usually conferred on the oil by incorporating special additives.
DEWATER – Removal of water from solids.
DIESEL FUEL – Petroleum product used as fuel for diesel engines.
DIFFERENTIAL PRESSURE – The difference in pressure between two points in a fluid system, usually in filtration systems expressed as ΔP between a housing inlet and outlet.
DIFFERENTIAL PRESSURE INDICATOR – An indicator that signals the difference in pressure at two points.
DIFFERENTIAL PRESSURE SWITCH – An electrical switch operated by the difference between two pressures and often used to give warning of the end of a filtration cycle.
DIFFERENTIAL RATING – Differential pressure is specified as the maximum an element can withstand without structural failure.
DIGESTED SLUDGE – Sludge or thickened mixture of water with sewage solids in which the organic matter has been decomposed by anaerobic bacteria.
DIRECTION OF FLOW – The direction in which product flows through the element; may be from inside to outside, from outside to inside, or end to end, depending on the design of the element.
DIRT HOLDING CAPACITY – Volume of contaminant an element can hold before reaching the maximum allowable pressure drop. Volume will vary depending on the element’s size and design and the solid particles’ density. Usually reported by weight such as grams or pounds per element and also called solids retention or solids holding capacity.
DISC PACK ELEMENT – Filter element constructed by packing alternate discs of filter medium and flow distributor plates into a compact cylindrical form.
DISCHARGE – Liquid that leaves the housing after passing through the medium. It may be different from filtrate, e.g., wash water discharge.
DISCHARGE LIQUOR – Liquid that has passed through the filter, also referred to as effluent, filtrate, mother liquor, solute, strong liquor, product, clean and dry product, etc.
DISCHARGE SOLIDS – Solids deposited upon the filter medium during filtration in sufficient thickness to be removed in sheets or sizable pieces and sometimes referred to as cake or residue.
DISPOSABLE FILTER ELEMENT – A filter element that is not cleanable and is therefore discarded and replaced at the end of its useful life (sometimes referred to as a throwaway or noncleanable element).
DISSOLVED SOLIDS – Any solid material that will dissolve in the liquid that is being filtered, such as sugar in water.
DISTILLATION – Process of vaporizing a liquid and collecting the vapor, which is then usually condensed to a liquid. In industry, this process is widely used to separate the components in a liquid solution. Since every pure compound boils at a specific temperature, it is often possible to boil off one liquid while most of the higher boiling point material remains in its liquid state. It is extremely difficult and sometimes impossible to separate materials in this way when they boil at the same or near the same temperature.
DIVIDER – Component of a housing: metal plate used to create chambers such as inlet and outlet chambers.
DOWNSTREAM – Portion of the product stream that has already passed through the system; portion of a system located after a filter, filter separator, etc.
DUPLEX FILTER – Assembly of two filters with valving to select either or both filters.
EDGE TYPE FILTER – A filter that entraps particles on the edges of the medium.
EFFECTIVE FILTRATION AREA – The area of filter medium exposed to flow and usable for its intended purpose: coalescing, filtering, or separating. Opposite of blind spots or dead area.
EFFICIENCY – The ability of a filter element to remove/retain a specific artificial contaminant in a specified concentration under controlled test conditions. Efficiency is expressed in percent (%).
EFFICIENCY CURVE – Graph showing the performance of a filter when challenged by specified artificial or natural contaminants under controlled conditions. Penetration or efficiency may be plotted against particle size at constant face velocity.
EFFLUENT – The discharged liquid from a filter, filtrate.
ELEMENT – Medium used in a housing to perform the function of coalescing, filtering, or separating. Also referred to as a cartridge, repack, etc.
EMULSIFICATION – The dispersion of one substance in the form of minute drops within another substance.
EMULSION – The dispersion of fine liquid particles in a liquid stream which do not necessarily dissolve in each other but are held in suspension. Many emulsions may be broken by coalescing if the liquids are immiscible. Emulsion stabilizers modify the surface tension of the droplets, which makes coalescing difficult, if not impossible.
EMULSION SEPARATION – Chemical methods of emulsion separation are regularly employed to remove the oil phase from spent emulsion cutting oils before disposal. The typical treatment is dosing with a divalent or trivalent metal solute. Thermal, electrical, and physical methods are also used. (Reference Coalescence)
ENGINE DEPOSITS – Accumulation of sludge, varnish, and carbonaceous residues on engine components.
ENTRAINED WATER – Discrete water droplets carried by a continuous liquid or gas phase when water is immiscible with the liquid. It may be separated from the continuous phase by coalescing and gravity separation and usually picked up in a system by condensation or a water washing used in the process.
FEED – Material to be filtered and referred to as concentrate, influent, intake, liquor, mud, prefilt, pulp, slime, or sludge.
FIBER MIGRATION – Carry‑over of fibers from the media used in coalescer, separator, or filter cartridges into the effluent. More definitive than media migration since fiber migration is qualitative.
FILM STRENGTH – The property of a lubricant that permits it to resist being ruptured or broken when under pressure between two metal surfaces.
FILTER – Term generally applied to a device that removes solid contaminates from a liquid or gas. As referred to in the industry today, a filter is limited to a device that removes solid contaminates only. If a device is used to remove solid and liquid contaminates, it is generally referred to as a separator, filter separator, or entrainment separator. The term filter is sometimes erroneously used to describe the medium used inside the housing or filter case, but the correct term should be filter element, cartridge, etc.
FILTER AID – Powders added to the liquid to be filtered to increase the porosity of the cake of solids formed on the filter septum, thus maintaining the permeability and the flow of filtrate, lengthening the operating cycle.
FILTER ASSEMBLY – A filtering device consisting of a housing and filter element that directs flow from an inlet port, through a filter element, and through an outlet port.
FILTER COALESCER – Single-stage, horizontal housing for coalescing and separating one immiscible fluid from another and removing solids. Generally recommended for use where the continuous phase has a light gravity. Available with various efficiencies.
FILTER ELEMENT – A porous device that performs the actual filtration process.
FILTER MEDIA – The porous structures upon which, or in which, fluid system contaminants are trapped.
FILTER SEPARATOR – Housing that removes solids and entrained liquid from another liquid or gas. It uses a combination of a baffle and/or coalescer, filter, or separator element. It may be single‑stage, two‑stage, or single or two‑stage with a prefilter section for gross solids removal. The common application is removing water from gas or another immiscible liquid. General reference to the term implies the equipment can both filter and separate to specific degrees of efficiencies.
FILTER SYSTEM – The combination of a filter and associated hardware required for the filtration process.
FILTERABILITY – Ease or difficulty of filtering.
FILTRATE – The liquid that has passed through the filter, effluent.
FILTRATION – The process of removing solid particles from liquid or gas by forcing them through a porous medium through which only the fluid passes.
FILTRATION BETA RATIO – The ratio of a number of particles greater than a given size (n) in the influent fluid to the number of particles greater than size (n) in the effluent fluid.
FILTRATION RATE – The volume of liquid that passes through a given area of filter in a specific time. Usually expressed as gallons per square foot per minute (or hour).
FINES – Particles which are smaller than a specified size.
FLOATING SCRAPER – Balanced scraper which, with minimum pressure, follows the contour of a drum.
FLOCCULATION – Process of small particles coming together to form larger ones, called flocs, and easier to filter. Also referred to as coagulation.
FLOW FATIGUE RESISTANCE – The ability of a filter medium to resist structural failure or deterioration from cyclic loading.
FLOW RATE – Rate at which product is passed through a housing or system; generally expressed as gallons per minute, barrels per hour, barrels per day, actual or standard cubic feet per minute, hour, day, etc. It is the same as the rate of flow.
FLOW RESISTANCE – Resistance offered by filter medium to fluid flow; the pressure difference required to give unit flow of a fluid of unit viscosity through a unit cube of filter medium.
FLUID – A term used in filtration and separation to include liquids, air, or gas as a general term.
FLUID COMPATIBILITY – The suitability of filtration media and seal materials for service with the fluid involved.
FRICTION – Resistance created by the surface of one object moving over the surface of another due to the interlocking of minute projections from the surfaces; this is called solid friction. If a lubricant is introduced between the two moving surfaces, fluid friction replaces solid friction.
FULL FLOW – Product flow through the housing at the rate for which the housing is designed to operate. It also refers to all products passing through the medium. Opposite of a bypass filter, which is designed to filter only a portion of the stream at a higher efficiency continuously.
FULLER’S EARTH – Clay; a hydrous aluminum silicate
GAS SCRUBBER – Housing designed to knock out liquid and solid contaminates by impingement on a series of baffles or demister pads. Accomplished by drastic reduction of velocity as the gas enters the scrubber. Entrainment separation would expand the term’s general use to include mechanical cartridge-type separators.
GPD – Gallons per day
GPH – Gallons per hour
GPM – Gallons per minute
GRAVITY FILTER – Filter in which the driving force for filtration is provided solely by the head of liquor above the filter medium (i.e., not employing pressure or vacuum to give a high differential pressure). Gravity filters often handle compressible materials or materials in the form of flakes, which would pack down and become impervious under high differential pressure.
GRAVITY SEPARATION – Separation of immiscible phases resulting from a difference in specific gravity by coalescing.
GREASE FILTER – An assembly consisting of either a coalescing section, an adsorptive section, or both.
HEAT OF ADSORPTION – Heat released when a substance is adsorbed; equivalent to the energy which the adsorbate must give up in going from its normal energy state to the lower energy state it has when adsorbed. The heat depends on the adsorbate and adsorbent.
HOLDING CAPACITY – Refers to the amount of solids, particulate, or foreign material one or more elements is capable of retaining up to the terminal or maximum differential pressure. It can also refer to the volumetric holding capacity of either a solid or a liquid.
HYDROPHILIC – Water accepting or water wetting. Having an affinity for water. Capable of uniting with or dissolving in water. Effective coalescing requires the medium to have hydrophilic characteristics, causing free or entrained water to commingle into droplets which, when mated with other droplets, form into drops which separate by gravity. Opposite of hydrophobic.
HYDROPHOBIC – Non‑water wetting (water rejecting). Not capable of uniting or mixing with water. Opposite of hydrophilic.
IMMISCIBLE – incapable of being mixed; insoluble; opposite of miscible.
IMPINGEMENT – Process of removing liquid or solid contaminates from a stream of compressed air or gas by causing the flow to impinge on a baffle plate at a high velocity. Contaminate falls off by gravity into a large quiescent sump area to prevent the contaminates from being picked up a second time by the velocity of the stream. It may also be used on liquid streams to separate solid contaminates.
IMPREGNATION – The infusion or saturation of a material with resin.
INFLUENT – Stream of fluid at the inlet of a filter or filter separator. It is the same as affluence and the opposite of effluent.
IN-LINE FILTER – A filter assembly whose inlet, outlet, and filter element have a common centerline.
INORGANIC – Not formed from a living substance; substances that do not contain carbon as a major constituent.
INSOLUBLE – Incapable of being dissolved in a fluid; opposite of soluble.
INSOLUBLES – Contaminants found in used oil due to dust, dirt, wear particles, oxidation products, combustion products, etc, often measured as pentant/heptain or toluene insoluble to reflect insoluble character.
INTAKE – Material to be filtered, also referred to as concentrate, feed, influent, liquor, mud, prefilt, pulp, slimes, or sludge.
INTERFACE – The surface over which the continuous phase and discontinuous phase are in contact.
INTERPLEAT – Pleating of two or more filter media into an element, such as glass fibers and cellulose.
ION – Any atom or molecule that has a resultant electric charge due to loss or gain of valence electrons.
ION EXCHANGE – Using zeolites, artificial resins, or immiscible liquids to capture anions or cations from solutions. Industrial applications include water softening, desalination and purification, solvent extraction, isotope separation, and the extraction of metals from ores.
JET FUEL – Petroleum product used as fuel for jet engines.
KIDNEY LOOP SYSTEM – A kidney loop system contains a pump/motor and an independent filtration unit. It is a compact, self-contained filtration system designed for high efficiency and high capacity, capable of removing solid particulate contamination not removed by the full-flow filters. A kidney loop system can run intermediately or continuously, helping to reduce costs and achieve and maintain proper ISO cleanliness levels.
KINEMATIC VISCOSITY – A measure of a fluid’s resistance to flow under gravity at a specific temperature (usually 40°C or 100°C).
L-TYPE FILTER – A filter assembly in which the inlet and outlet ports are positioned at 90° to each other.
LEAF – A support for the filter medium.
LIFE EXPECTANCY – The amount of use that may be expected from an element before it must be replaced will vary according to the element’s characteristics, operating conditions, and influent conditions.
LIQUOR – Material to be filtered; also referred to as concentrate, feed, influent, intake, mud, prefilt, pulp, slimes, or sludge.
LUBE OIL CONDITIONER – A lube oil conditioner (oil filtration system) is designed to maintain lube oil within the engine and turbine OEM manufacturers’ specifications for water and solid particle contamination, effectively extending the life of the lubricating oil.
LUBRICATION – Substituting fluid friction for solid friction by inserting oil between two moving parts.
MANIFOLD – A pipe or assembly that connects the filter elements to form one common discharge for the filtered product.
MEAN FILTRATION RATING – A measurement of the average pore size of the specific filter medium.
MEDIA – The material that performs the actual separation of solids from liquids.
MEDIA MIGRATION – Separation and/or deterioration of components of the filter medium and subsequent release into the effluent.
MEDIUM – The principal component of an element. The porous material that performs the actual process of filtration.
MEMBRANE FILTER – A thin permeable film of inert polymeric material cast in such a way, from a mixture of solvents, so that the size, number, and shape (tortuosity) of the pores is controlled.
MESH (WIRE CLOTH) – Number of openings, or fractions of openings, in a linear inch of wire cloth.
MICROMETER or MICRON – A unit of length. A micrometer is one-millionth of a meter or 0.000039″ (39 millionth’s of an inch). Expressed in convenient terms, 25 Micrometers is approximately equal to one-thousandth of an inch (0.001″). The naked eye can see a particle that is 40 microns or larger.
MICROORGANISMS – Living bodies that can be seen only through a microscope.
MIGRATION – Contaminant released downstream of a filter.
MULTI-PASS TEST – A test used to determine the Beta Ratio of a filter element.
MULTIPLE CARTRIDGES – Two or more cartridges fastened together end to end to make up one element.
NEGATIVE PRESSURE – Vacuum or suction.
NOMINAL FILTRATION RATING – An arbitrary micrometer value established by a filter manufacturer to indicate filtration capability.
OFFLINE OIL FILTRATION – A portable or fixed supplemental filtration system designed to help achieve ISO cleanliness levels. (Reference Kidney Loop System)
OIL CENTRIFUGE – A mechanical device that uses centrifugal force to separate impurities and contaminants from oil.
OIL DEGRADATION – Lubricant degradation occurs throughout the service life of the lubricants, depending on the oil type, the temperature, the operational conditions, and the environment. The baseline for change occurs when further deterioration leads to a level whereby the lubricant can no longer protect the system. When oil degrades, it changes composition and functional properties, and unwanted products are formed: acid compounds, soft contaminants (also called sludge/resins (dissolves in warm oil)), and varnish (deposit formation).
ORGANIC – Describes the vast number of chemical substances containing carbon, hydrogen, and oxygen.
ORGANIC SOLVENTS – Substances in which an organic material will dissolve.
OSMOSIS – Diffusion of a solvent through a semi‑permeable membrane from a dilute solution into a more concentrated solution, thus tending to equalize the concentration of each side of the membrane.
OUTER SHELL – The outer covering of an element, usually perforated or screened.
OUTER WRAP – The outside covering of an element.
OUTLET (FILTRATE OUTLET) – Ports integrally formed in a filter plate through which filtrate can escape from the filter chambers.
OUTSIDE-IN – Flow of product from outside to inside of element.
OXIDE – A combination of oxygen with another element.
OXIDATION – A chemical combination of any substance in which the oxidation state (positive valence) of an element is increased.
PACKED BED – Discrete materials such as sand, gravel, anthracite, fabricated rings or saddles, assembled in a confined space as a filtration medium for liquids or gases.
PAPER – Medium used in many elements. A very general term applied to resin-impregnated cellulose. Many types of paper or cellulose, made to specification, are used as a filter medium.
PARTICLE – A single piece of solid material that is small in relation to its environment. Usually characterized by its size and shape.
PARTICLE COUNT – The practice of counting particles of solid matter in groups based on relative size. It is frequently used in engineering a filter to a specific task or to evaluate the performance of a filter under specific operating conditions. When used as data to engineer a filter, proper consideration can be given to the type of medium to be used, the expected life of the medium, and the actual cost of operation.
PARTICLE SIZE DISTRIBUTION – The distribution obtained from a particle count grouped by specific micron sizes.
PARTICULATE – Relating to minute, separate particles.
PERFORATED – Material in which holes have been punched, such as the material used to make the center tube of a cartridge.
PERMEABILITY – The relationship of flow per unit area to differential pressure across a filter medium.
PERMEABLE – Material that has openings through which liquid will pass in filtering. Also referred to as porous or pervious.
pH RANGE – A pH scale measures how acidic or basic a substance is, ranging from 0 to 14. A pH of seven (7) is neutral, a pH less than seven (<7) is acidic, and a pH greater than seven (>7) is a base.
PHOSPHATE ESTER BASE FLUIDS – Fire-resistant hydraulic fluids.
PLEATED – A physical form of a cartridge made into a convoluted form to resemble the folds in an accordion.
POISE (ABSOLUTE VISCOSITY) – Numberically equal to the force required to move a plane surface of one square centimeter over another plane surface e at the rate of one centimeter per second when the surfaces are separated by a layer of fluid one centimeter in thickness (dyne sec/cm²).
PORES – A small channel or opening in a filter medium that allows fluid passage.
PORE SIZE DISTRIBUTION – The ratio of the number of holes of a given size to the total number of holes per unit area is expressed as a percent (%) and as a function of hole size.
POROSITY – The ratio of pore volume to total volume of filter medium expressed as a percent (%).
POROUS – Material that has openings through which liquid will pass in filtering. Also referred to as permeable or pervious.
POTABLE – Drinkable (water).
PPM (PARTS PER MILLION) – A unit of concentration.
PREFILT – Material to be filtered; also referred to as concentrate, feed, influent, intake, liquor, mud, pulp, slimes, or sludge.
PREFILTER – Filter for removing gross contaminants before the product stream enters a filter separator.
PREFILTER COALESCER – Two‑stage, horizontal housing for efficient solids and water removal at high flow rates. Used on light gravity streams.
PREFILTER COALESCER SEPARATOR – Three‑stage housing for use where stream carries an unusually high amount of solids; prefilter elements in first stage remove bulk of solids and permit coalescer and separator elements in next two stages to function more effectively for phase separation.
PRESSURE RELIEF – A valve that permits enough liquid or gas to escape from the housing to prevent extreme pressure buildup within the housing.
PRETREATMENT – Changing the properties of a liquid‑solid mixture by physical or chemical means to improve its filterability. Chemical means include coagulation, flocculation, and conditioning; physical means include size classification, preaeration, mechanical agitation, freezing and thawing, heating, ultrasonic and mechanical vibrations, electronic and magnetic treatment, and ionizing radiation. Filter aids are also used for pretreatment.
PSI – Pounds per square inch.
PSIA – Pounds per square inch absolute = PSIG (guage) + atmospheric pressure (14.696).
PSID – Pounds per square inch differential, ΔP.
PSIG – Pounds per square inch gauge = PSIA minus atmospheric pressure (14.696). That pressure registered on a conventional type gauge.
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.
REGENERATED – Cleaned of impurities and made reusable.
RESIDUE – Solids deposited upon the filter medium during filtration in sufficient thickness to be removed in sheets or sizable pieces, sometimes referred to as cake or discharged solids.
REVERSE OSMOSIS – The reverse of natural osmosis achieved by external application of sufficient reverse pressure to cause solvent flow in its unnatural direction through a membrane, that is from the more concentrated to the dilute solution.
SAE NUMBER – Classification of lubricating oils for crankcases and transmissions in terms of viscosity as standardized by the Society of Automotive Engineers.
SAND FILTER – Filter composed of layers of sand graded in particle size so that the coarser particles face the unfiltered flow. Commonly employed in the filtration of water supplies. Filters of this type (perhaps incorporating crushed coke and grit) have occasionally been used for the removal of particles from gases.
SECONDARY OIL FILTER – Designed to clean less than ten percent (10%) of the engine lube oil used to remove contaminants that the primary oil filter has not removed from the lube oil. The engine oil flows through the secondary oil filter is diverted back to the oil sump before reaching the primary filter. The bypass filter captures smaller particles than the full-flow oil filter. It is another term for bypass filtration.
SEDIMENTATION – Action of the settling of the suspended solids.
SELF-CLEANING FILTER – A filtering device that cleans itself using a blowdown or backwash action. The medium is commonly a screen mounted on a cylindrical drum or device that removes bulk solids from large flow rates. A baffle or strainer (mesh) in the first stage aids in separating solids by impingement. Blowdown may be continual or intermittent and operated either manually or automatically by instruments.
SEMI-DEPTH TYPE FILTRATION – The retention of contamination both on the surface and within the internal pore structure of the medium.
SEPARATION – Action of separating solids or liquids from fluids. This may be accomplished by impingement, filtration, or coalescing.
SEPTUM – Any permeable material that supports the filter media.
SERVICE LIFE – Length of time an element operates before reaching the maximum allowable pressure drop.
SHELL – Outer wall of a housing. Also referred to as a body or housing.
SILICA – Abrasive contaminant (example, catalytic fines, dust particles (example, from landfill gas). Very abrasive, resulting in excessive wear.
SINGLE-STAGE FILTER SEPARATORS – Liquid or air/gas filter separators containing only one type or kind of replaceable element instead of two‑stage, three‑stage, or four‑stage filter separators.
SINTERED FILTER MEDIA – Porous media formed by packing and fusing together a thin layer of metal or plastic particles or fibers.
SLOC – Specific lube oil consumption, based on g/kWh or g/bhph
SLUDGE – Residues and deposits occasionally formed by oils after extended use; material to be filtered, also referred to as concentrate, feed, influent, intake, liquor, mud, prefilt, pulp, or slimes.
SLURRY – Filter feed material in which the solids content is appreciable, such that the solids can easily be seen.
SOLIDS – Mass or matter contained in a stream, considered undesirable and should be removed; that part of the discontinuous phase removed from liquid or gas through filtration.
SOLUBLE – Capable of being dissolved in a fluid. Opposite of insoluble.
SOLUTE – A liquid that has passed through the filter and also referred to as discharge liquor, effluent, filtrate, mother liquor, or strong liquor.
SOLVENT – Substance, usually a liquid, in which another substance becomes dissolved; solvent will generally comprise the greater part of the solution.
SPECIFIC GRAVITY – The ratio of the weight of a given volume of matter to the weight of an equal volume of water.
SPIN-ON-FILTER – Cartridge filter in which the filter body and the filter element have been constructed as an integral disposable item. Filter change is quick by spinning off the used unit from a fixed filter head and quickly spinning on a replacement unit.
STOKES’ LAW – A physical law that approximates the velocity of a particle falling under the action of gravity through a fluid. The particle will accelerate until the frictional drag of the fluid balances the gravitational acceleration, after which it will continue to fall at a constant velocity known as the terminal or free-settling velocity.
SSU (SAYBOLT SECONDS UNIVERSAL) – A measure of viscosity. The time in seconds for 60 cubi centrimeters (cc) of liquid to flow through a standard orifice at a specific temperature.
STRAINER – A course or relatively open filter element, usually greater than 50 micons.
STRATIFICATION – Condition in which the larger particles settle out below the finer ones. Also referred to as a classification.
STREAM – Term sometimes used and synonymous with the words product, liquid, etc., in speaking of any matter processed by filtration or filtration separation equipment.
SURFACE TYPE FILTRATION – A filter medium that primarily retains contaminant on the influent face.
SUSPENDED SOLIDS – Solids that do not dissolve in liquid; those that remain suspended and can be removed by filtration.
SUSPENSION – Any liquid containing undissolved solids.
SYSTEM SILTING – The agglomeration and settling of ultrafine particles in a fluid system.
TEE TYPE FILTER – A filter assembly whose inlet and outlet ports are on a common center line at right angles to the axis of the filter element. Features element replacement without disturbing system connections.
TERMINAL VELOCITY – Steady velocity achieved by a falling particle when gravitational forces are balanced by viscous forces. (Reference Stokes’ Law)
TORR – The unit of pressure used in vacuum measurement; equal to 1/760 of a standard atmosphere.
TOTAL BASE NUMBER (TBN) – Expresses the quantity of acid required to neutralize all basic components in a sample (of e.g., lubricating oil); i.e., high TBN indicates high alkalinity.
TRAMP OIL – Free oil contained in emulsion-type machine tool coolants. This may be caused by machine leakage or the breakdown of the emulsifying agents in the cutting oil. Impairs the efficient operation of some types of cutting oil filters and is often removed by rotating the steel drum of belt skimmers.
TRANSMISSION – Percentage of contaminant that passes through filter or filter medium. Penetration and transmittance have the same meaning.
TRIBOLOGY – The science of lubrication, friction, and wear.
TRUNK PISTON DIESEL ENGINE – A medium-speed or high-speed engine generally uses the same oil for both cylinder and crankcase lubrication and utilizes connecting rods to transmit piston power directly to the crankshaft rather than through a crosshead.
TURBIDITY – Any insoluble particle that imparts opacity to a liquid.
TURBINE – A piece of equipment in which a shaft is steadily rotated by the impact of a current of steam, air, water, or other fluid directed from jets or nozzles upon the blades of a wheel or series of wheels.
TURBOCHARGER – A compressor driven by an exhaust gas-driven turbine that supplies air at higher pressure to the engine to increase power.
ULTRAFILTRATION – Separation of colloidal solids from liquids through semipermeable medium.
UNLOADING – The removal of a contaminant that was previously trapped or retained by the filter medium.
UPSTREAM – Portion of the product stream that has not yet entered the system.
VACUUM DISTALLATION SYSTEM – A Vacuum dehydration oil conditioning system that keeps industrial oils free of water and particulate contamination to achieve long-term, predictable, and profitable performance. A vacuum dehydration system uses the vacuum dehydration-distillation method to remove water and solid particles from industrial oils. These oil pressure filtration systems are excellent purification solutions for high-viscosity oils and poor water-shedding oils.
VARNISH – Varnish (also known as lacquer, sludge, or tar) is a detrimental by-product of oxidation, additive drop-out, and thermal degradation of lube oil. Varnish in lube oil systems is a serious maintenance concern for operators of rotating equipment, particularly gas turbines, compressors, and paper machines. Oils can potentially create varnish, an insoluble film that forms inside the lubrication and hydraulic systems. If left unchecked, varnish contamination leads to valve sticking and the formation of deposits on metal surfaces throughout these systems. If these deposits occur on heat exchangers or reservoir walls, the varnish reduces the equipment’s ability to transfer heat from the system.
VARNISH REMOVAL SYSTEM – A varnish removal system provides continuous kidney-loop filtration and circulation of the oil reservoirs to effectively remove soluble and suspended varnish.
VISCOSITY – Degree of fluidity. A measure of the internal friction or the resistance of a fluid to flow. The standard unit of measure is poise, stoke, or SSU.
VOIDS – Openings in the medium or filter cake.
WASTE – Material removed, rejected, or otherwise lost in various manufacturing processes.
WIRE CLOTH – A metallic filter medium formed by weaving fine wires into a cloth with controlled pore size.
YOKE – The end cap is used to hold a cartridge in place.
Separator Spares & Equipment is here to help you meet and exceed your reliability and filtration requirements. We offer different types of complete filtration solutions and spare filter parts (including elements, housing, and filter aids). We regularly partner with customers to tackle specialized oil and fuel filtration challenges. Our reliable filtration, coalescing, and distillation dehydration solutions, key manufacturer-engineered products, and engineering teams ensure that our supplied equipment performs as requested and projects are completed.
Separator Spares & Equipment helps bring fluid contamination problems under control. Let us help you keep your equipment’s maintenance schedule on track while maximizing uptime across your entire operation. We allow you to save money without losing quality.