Here is a glossary of Filtration Terms and their meanings.  Please refer to the Machine Coolant Filtration Index for articles and information on these topics.

A  |  B  |  C  |  D - F  |  G - M  |  N - R  |  S - Z

A:

Abrasion:  Migration of foreign material which enters the fluid stream from system components that wear from close tolerances, vibration, or shock. 

Absolute:  An arbitrary term used to describe or define a degree of filtration.  The filtration industry uses various methods of determining absolute ratings which are not necessarily interchangeable.  Generally ‘absolute’ references 100% removal of solids (glass beads) above a specified micron rating on a single pass basis.  See nominal. 

Absolute Pressure, The total pressure exerted, including atmospheric pressure.  Pressure is defined as force per unit area.  See differential pressure, gauge pressure, head pressure, static pressure. 

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.  See article on Why filter clean finer than their ratings. 

Absorb:  To intercept, or drink in.  To suck in, as a sponge sucks in water.  See adsorbent. 

AC Coarse, AC Fine, See Arizona Road Dust. 

Accelerator:  To hasten action.  Also used to describe an auxiliary valve to hasten fluid action. 

Acetate Rayon:  A fiber or filamentous material made by the acetate process.  Differs from other rayons in that it is not regenerated cellulose, but an ester of cellulose, namely cellulose-acetate.  Has different physical and chemical properties from other rayons especially in its reactions to dyes. 

ACFM:  Actual Cubic Feet per Minute.  Measured at operating temperature and pressure. 

Acid:  A large class of compounds which contain the element hydrogen (H-) in its formula which may be replaced by metallic salts.  Of primary concern is the deleterious effect most acids may have on filter media and vessels. 

Acidity:  The quality, state or degree of being acid.  In lubricating oils, acidity denotes the presence of acid-type 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.  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 and other carbonaceous matter, but must be activated by high temperature steam or carbon dioxide which creates a porous particle structure. 

Activated Charcoal:  See activated carbon. 

Activated Sludge:  Biologically active floe from aeration and settling sewage and/or organic matter. 

Adiabatic:  Insulated and neither heated nor cooled; as in an “adiabatic change”, wherein a condition is altered without gain or loss of heat. 

Adsorb:  The phsysio-chemical phenomenon involved to attract and hold a gas, vapor, or liquid on the surface of a solid, particularly on a finely divided material. 

Adsorbate:  The material which is adsorbed; I.e., the gas, vapor, or liquid which adheres or is chemically attracted to the surface of the solid. 

Adsorbent:  A material which adsorbs; I.e., the solid which attracts and holds on its surface the gas, vapor, or liquid.  Also materials added to liquors to decolorize or purify by adsorbing the color of impurity.  Fuller’s earth, activated carbon, activated alumina, etc. are all adsorbents. 

Adsorbtion:  The natural phenomenon of a gas, vapor, or liquid being attracted to and held on the surface of a solid. To some extent adsorption takes place on any solid surface, but certain materials have sufficient adsorbent capacity because of the finely divided material to make them useful in such industrial applications as the purification and separation of gases and liquids. 

Aeration, Sparging air or cascading liquid in a manner that the liquid will come  in contact with air.  Usually used when oxygen will cause desirable chemical or biological reactions in the liquid. 

Aerobic Bacteria, Bacteria which requires the presence of oxygen for growth.  Also see the Article on Bacteria in Coolant. 

Aerosol:  A liquid or solid particle suspended in air, gas, or vapor. 

Affluent:  Fluid entering the filter or separator/filter.  More commonly described as influent.  Opposite of effluent.               

Aggregate:  Fluid mixture of concentrated solids to be filtered. 

Air Eliminator:  Float-operated valve to evacuate air or gas from a vessel or chamber. 

Alkali:  A term that applies to the type of compounds which have basic properties and which will neutralize acids.  Some alkaline materials are hydroxides, carbonates, caustics, etc. 

Alkylation:  A petroleum refining process. 

Ambient:  Surrounding.  For example, ambient operating temperature of a vessel is temperature essentially the same as that surrounding the vessel. 

Amorphous:  Non-crystalline, having no determinable form or crystalline form.  Solids to be removed by filtration may by amorphous. 

Anaerobic Bacteria, Bacteria which grows in the absence of oxygen. 

Anchor Bolt Plan:  Arrangement of mounting devices to hold a vessel in position.  Specific location of bolting to anchor a vessel. 

Anhydrous:  Free from water. 

Aqueous Contaminant:  Water contaminant. 

Area:  The available apparent surface exposed to the flow of a fluid for maximum utilization.  Function of the area in filtration is related to initial pressure drop, rate of flow, and solids retention capacity.  In many applications, proper utilization of area of media produces greater efficiency and solids retention.  This is accomplished by pleating of material into an accordion form to produce increased surface area much greater than in a cylindrical form. 

Arizona Road Dust, Standardized test dust classified from natural Arizona dust.  Commercially available as AC Fine and AC Coarse 

Aromatic Compounds:  Compounds related to six-carbon membered rings as benzene or its derivatives. 

Asbestos:  A group of impure magnesium silicate minerals which are found in fibrous form.  Serpentine type is used for insulation, linings, and gaskets.  Amphibole type is used as filter material or filter aids in chemical applications. 

ASME:  American Society of Mechanical Engineers.  Publish code which governs the design of pressure vessels. 

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 vessel.  Final assembly would be used to name the action of assembling all items into an end product. 

Asymetric Membrane, A membrane with very small pores on one surface and progressively larger pores through the depth of the membrane structure.  Asymetric membranes usually have a very thin skin of small pores.  Minimizing the length of the small pores results in relatively low pressure loss across the pores. 

Atmospheric Pressure: The pressure of approximately 14. 7 pounds per square inch exerted at sea level in all directions by the atmosphere. 

Attrition: Wear caused by rubbing or friction. Produces fine particles that usually contaminate liquids which surround the point of attrition. Sometimes referred to as scouring or scoring. 

Avogadro’s Law:  Sometimes referred to as Avogadro’s principle.  Equal volumes or different gases under the same conditions of temperature and pressure contain the same number of molecules.  See also Boyle’s Law and Charles’ Law.

B: 

Backwash:  To reverse flow air, stream, or fluid through the media to effect solids removal.  Sometimes referred to as blowback. A method of cleaning a filter by reversing the flow to push off the accumulation of contaminants. 

Bactericide, An agent used to kill bacteria.  Bactericides are sommonly used in machine coolant fluids to prevent bacteria growth in water based emulsions. 

Baffle: Component of a vessel which constitutes a stage when used; removes liquid and solids by impingement; may be either upstream or downstream of the basic filter media. May also be a plate to protect filter elements from the velocity of flow into a vessel. 

Basis Weight, Weight per unit area.  Basis weight is one of the specifications for fibrous materials, roll goods and filter media.  Typical units are grams per square meter or ounces per square yard. 

Basket:  element for a basket strainer.  A device normally using a screen as it medium for removal of coarse bulk solids. 

Basket Strainer:  Vessel for the removal of coarse bulk solids from liquid, air, or gas; element is a basket covered with a screen of a given mesh. 

Batch:  The quantity of material prepared or required for one operation.  Example:  a batch may be exemplified as a discontinuous process, such as batch processing of paint, soap, etc. 

Baume Gravity:  An arbitrary scale expressing the gravity or density of a liquid.  Water is 10° BE. 

Belt Skimmer, A tramp oil remover in the shape of a continuous belt which dips into the liquid to attract  floating oils and contaminants 

Blind Spots:  Places in medium where no filtering occurs.  Also referred to as dead areas.  Opposite of effective area. 

Blinding:   Where filtered-out particles fill the openings in the medium to the extent of shutting off the flow of product; loading up of the medium so as to reduce capacity.  Also referred to as blocking or plugging. 

Blowback:  To reverse flow air, steam, or fluid through the media to effect solids removal.  Sometimes referred to as backwash. 

Blowdown:  The action to evacuate liquids or solids from a vessel by use of pressure. 

Body:  A vessel containing the filter media.  Also referred to as housing. 

Boyle’s Law:  IF the temperature of a given kind of gas is held constant, the volume of a sample gas varies inversely with the pressure.  See also Avogadro’s Law and Charles Law. 

Breaking Strength:  Average force required to break a test specimen by tension. 

Breakthrough:  Used to describe the passing of solids through the cake built up on a filter media.  Also referred to as the breakpoint. 

Bubble Test:  Measurement of the largest opening in an element by determining the minimum pressure required to force air or a gas through the element while submerged in alcohol or other liquid.  Used as a quality control bench mark to determine of a surface type separator or filter cartridge meets the same value as the prototype cartridge. 

Bulk Density Ratio:  Ratio of total mass or weight of the material divided by the volume. 

Buna N:  Gasket material.  A synthetic rubber frequently used for vessel closures, flanges and filter elements. 

Burst Pressure:  The maximum pressure a vessel will safely withstand. 

Bursting Strength:  Force required to burst a vessel.  Example:  burst pressure may be 100 psi. while bursting strength may be 175 psi. 

Bypass:  Condition resulting from the product flowing through a vessel other than through the media.  Also a filtering system which filters only part of the stream on a continuous basis. 

Bypass Valve:  Valve to pass the flow around the media or the vessel, usually activated at a given differential pressure setting.

C: 

Canister:  Container or mounting mechanism for elements.  May be an actual part of and performing a function of the elements, or may be used to hold the element in position. 

Cap, Element:  Component which covers one end of an element and holds the element in place in the vessel.  Sometimes called a yoke. 

Capacity:  Volume of product which a vessel will accommodate.  This is expressed in gallons or similar units.  Also amount which will filter at a given efficiency and flow rate, expressed in gallons per minute or similar units. 

Capillary:  Fine, hair like tube having a very small opening. 

Cake:  Solids deposited on the filter medium during filtration in sufficient thickness to be removed in sheets or sizable pieces.  In many cases, cake may provide its own filter media by adding to the surface of media.  Also referred to as discharged solids or residue. 

Cake Release:  Ability of a medium to allow clean separation of the cake from the medium. 

Cake Repuddling:  Breaking cake structures for reformation. 

Calendered Wire Cloth:  Wire cloth that has been passed through a pair of heavy rollers to reduce the thickness of the cloth or to flatten the intersections of the wires and provide a smooth surface.  The term “rolled” is often used. 

Calibrating Tank:  A tank for calibrating capacity to provide volumetric proof of the delivery of liquids by positive displacement meters.  Also referred to as meter proving tank. 

Carding:  One of the most important processes in yarn manufacture.  It removes most of the impurities and a certain amount of the short, broken, or immature fibers; the maximum fibers are rearranged and delivered in the form of comparatively thin and light sliver, which is an entirely different form from the way it entered.  Carding should not be confused with combing.  The machine used is known as a card and there are different types for cotton, wool, worsted, etc. 

Carrying Body:  Liquid in which the solid particles are suspended. 

Cartridge:  Medium used in a vessel to perform the function of coalescing, filtering, or separating.  Also referred to as element, media, repack, etc.  Made in a specified physical shape, to be mounted by use of hardware designed for that purpose. 

Catalyst:  A substance which accelerates a chemical reaction without itself taking part in the reaction.  For example, alkylation will not take place unless some substance such as sulphuric acid is present; such a substance is called a catalyst. 

Caustic:  A class or a name given to a group of chemicals, usually caustic soda or sodium hydroxide.  A substance which has the power to burn, corrode, or eat away.  Used in chemical manufacture, petroleum refining, pulp and paper, detergents, soap, textiles, and vegetable oil refining. 

Cellulose:  The preponderant and essential constituent of all vegetable tissues and fibers.  Basic in the textile and paper making industries.  Three types exist in alpha-cellulose, beta-cellulose, and gamma-cellulose.  Material used in filter media is bond by impregnation, usually a phenolic resin.  Process of manufacture controls the basic weight and pore size to specification.  Filter paper, when impregnated with other properties, produces an excellent hydrophobic membrane which is non-water wetting and is used in the second stage of two stage separation/ filtration equipment.  Ideal cellulose material provides for a variety of filtration efficiencies, low initial pressure drop, high wet strength, and solids retention. 

Cellulose Acetate Rayon:  Rayon made by the acetate process; technically, acetate rayon filaments are composed of acetic ester of cellulose which has been coagulated or solidified from the solution.  See acetate rayon. 

Center Core:  Material formed into a tube or cylinder for structural purposes to permit a cartridge to retain its original physical form.  May also be the basic media, formed with sufficient strength so as to serve the purpose of a center tube. 

Center Pipe:  Component of a vessel which is used as a mount for cartridges made with perforated effect to accommodate flow.  A center rod is used for the same purpose but is not perforated and does not accommodate flow. 

Center Road:  Component of a vessel used for mounting cartridges in the vessel.  Usually made of a round bar material.  A center pipe may also be used for the same purpose but is made with perforated effect and directs flow through the cartridge. 

Center Seal:  Part which forms seal between two elements when one element is on the top of another element.  May also be called an adaptor. 

Center Tube:  Component of an element or cartridge which supports the medium at the center of smallest diameter. 

Centipoise:  One one-hundredth of a poise.  A poise is the unit of viscosity expressed as one dyne per second per square centimeter. 

Centistoke:  One one-hundredth of a stoke.  A stoke is equal to the viscosity in poises times the density of the fluid in grams per cubic centimeter. 

Chain Weave:  A compact, heavyweight weave made with plied yarn in both directions; identified by pattern of two up and two down broken twill, two ends of right hand and two of left hand, repeated on four threads each way.  Although its tensile strength may be low, it affords both high filtrate clarity and high flow rates. 

Channel:  To cut grooves or lines in or through the solids deposited on the media, or through the media itself.  Also may be described as a breakthrough in the media which would result in a bypass. 

Charles Law:  If the pressure on a given kind of gas is held constant, its density is inversely proportional to its absolute temperature.  See also Avogadro’s Law and Boyle’s Law. 

Cheesecloth:  A loosely woven, light weight, open construction cotton fabric made from carded print cloth yarns and using the plain weave.  The name is derived from the original use, which was a wrapping for pressed cheese.  Now widely used for bandages and surgical gauze as well as many other purposes when converted. 

Chemical Polarity:  An attribute of a chemical or family of chemicals, whose arrangement of atoms around the nucleus is not symmetrical.  This makes them much more chemically reactive than symmetrical chemicals. 

Chlorinate:  To combine chemically with chlorine. 

Clarification:  Filtration of liquids containing small quantities of suspended solids; filtration takes out most of these solids and increases the clarity of the liquids. The filtration of liquids containing small quantities of suspended solids, resulting in improved clarity of the liquid. 

Clarity:  The amount of contaminates left in a filtered liquid; the absence generally indicates the liquid to be free of contamination to an unspecified degree. 

Classification:  A condition in which the larger particles settle out below the finer ones.  Also referred to as stratification.  May also be referred to as the action to sort out particles by various size groups or to some other 

Clean-in-Place, A term used to describe a type of system used for sanitary processing.  A clean-in-place design allows equipment to be cleaned to sanitary standards by simply flushing cleaning agents through the system. 

Clean Pressure Drop:  The differential pressure (drop) across a vessel, measured in pounds per square inch at rated flow on new elements with clean product. The differential pressure (drop) across a vessel when the fluid is flowing through new filters.  Also called Initial Pressure Drop. 

Closed Loop, A system where the total amount of liquid is recirculated. 

Coagulant:  That which produces coagulation or agglomeration of suspended solids. 

Coagulation:  The growing together of minute particles to form larger ones, which are called flocs and are easier to filter.  Also referred to as flocculation. 

Coalesce, A device that separates a suspended liquid from a suspending liquid by intercepting and coalescing droplets of the suspended liquid while allowing the suspended liquid to pass through.  The drops of intercepted liquid typically coalesce into large enough droplets to allow gravity separation. 

Coalescer:  A mechanical device which unites discrete droplets of one phase prior to being separated from a second phase.  Can be accomplished only when both phases are immiscible.  Requires a tight media which is preferentially wettable and, by its nature of being tight, the media is also a good filtering material.  Good coalescing permits gravity separation of the discontinuous phase.  Coalescing may be accomplished by only a coalescer cartridge when the specific gravities of the two phases are widely separated.  As the gravities’ difference becomes less, the two stage principle is generally required where finely coalesced discontinuous droplets are repelled by the second stage separator cartridges. 

Coalescing:  The action of uniting of small droplets of one liquid preparatory to its being separated from another liquid. 

Code:  Generally refers to vessel design.  A standard to which a vessel may be fabricated.  As an example, the design may meet the requirements of Section VIII, ASME Code for unfired pressure vessels.  When used in referring to other standards, the full code title should be given. 

Colloid, A stable dispersion of very small particles in liquid. 

Colloidal Particles:  A gelatinous substance of minute particles which remain in suspension. 

Combing:  The process of treating cotton, wool, etc. in a comber.  Combing removes those fibers below a desired length, combs the fibers that are retained and arranges them in parallel order, and takes out dirt, etc. which are not removed in previous processes.  Combing is necessary for the production of fine yarns and is also used on coarser yarns when high quality is required. 

Compatibility:  Capability of two or more materials or substances to be used together without ill effect.  Factor must be considered when choosing the medium to be used with any fluid stream. 

Composite Media:  Media made up of more than one material. 

Compressibility:  Degree of physical change in filter cake particles when subjected to normal pressures.  Also a factor to consider when selecting gasket material. 

Concentrate:  Material to be filtered.  Also referred to as feed, influent, intake, liquor, mud, prefilt, pulp, slimes, or sludge. 

Concentration Ploarization, An undesirable condition that can exist at the surface, of a reverse osmosis membrane. 

Condensation:  The process of cooling a vapor below its boiling point in order for it to be liquefied. 

Conditioning:  Improving the filtering qualities of the filter feed. 

Consistency:  Degree of density or firmness, especially of thick liquids.  Thus a product of light consistency is almost fluid, while a product of heavy consistency is thick, and in some liquids it may be hard. 

Consistency of Feed:  Usually refers to the ratio of solids to liquid in the feed. 

Contaminate:  The foreign matter in a fluid which is accumulated from various sources such as system dirt, residue from wear of moving parts, 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 the efficiency of a fluid.  Water as well as 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 separator/filters are sought. 

Contaminant, The foreign matter in a fluid, which is usually undesirable.  Contaminants may cause discoloration or haze in a liquid, abrasion or wear on surfaces, system upsets in process systems, disease in living things.  Contaminants are the reason why filtration is necessary. 

Continuous Phase:  The basic product flowing through a filter or separator/filter which continues on through a system after being subjected to solids and/or other liquid separation. 

Conversion:  Change of type of elements in a vessel to vary the efficiency.  May also refer to the adaptor hardware to provide for use of elements in competitive equipment, sometimes called retrofit.  In general, it refers to the changing of one type media to another type for a specific purpose. 

Convolution:  Used to describe one pleat of a pleated surface type element usually in the shape of a “V”.  Also refers to the twisting or coiling of a cotton material as well as the irregular spiral or screw like condition of mature cotton.  Generally, the finer fibers have more twists. 

Convolutions:  Twisting or coilings.  Used to describe one complete pleat of an element. 

machine coolant:  Liquid used in industrial processes to cool, lubricate and flush away contaminants from the work area.  Also see articles on Machine Coolant and types of Machine Coolant. 

Core:  Material used for the center of an element; generally of the wound design.  May also be called a center tube when used in the coalescer, separator, or other type filter element.  May also be a tube of fibers formed into an element which has sufficient strength so as to provide its own center core. 

Critical Operating Pressure:  Pressure above which filtration or separation equipment may produce reduced efficiency or fail to function properly. 

Cross Flow Filtration, A filter system with one inlet and two outlets. Liquid passing through the filter medium is called the per­meate. Liquid that exits the filter without go­ing through the filter medium is called the concentrate ( or retentate) because unwanted components of the feed liquid are carried out of the filter in the concentrate stream. This technique is commonly used in reverse osmo­sis systems and ultrafiltration. See dead end filtration. 

Cryogenics:  The field of science dealing with matter at very low temperatures.  In filtration, the extremely low temperature negates the use of many media, gaskets, at certain type vessels. 

Cycle:  The actual interval of filtration, expressed in units of time; hours or days. 

Cyclically:  Operating in cycles. 

Cyclone:  Liquid or gas filter using the principle of centrifugal force which causes the contaminate to settle to the bottom of the vessel without the use of fiber media. 

Cylindrical:  Having round sides, the ends being equal circles.  Opposite of pleated when used to describe elements.