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Filtration Glossary continued s-z

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Filtration Glossary continued s-z

Machine Coolant Filtration Glossary

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 - C  |  D - F |  G - M  |  N - R  |  S  |  T  |  U  |  V  |  W  |  X  |  Y  |  Z


SAE Number:  A classification of lubricating oils for crankcases and transmissions in terms of viscosity as standardized by the Society of Automotive Engineers.

 Sacrificial Element,  A metal allowed to corrode by galvanic attack so that more critical components are not corroded. 

Saybolt Seconds Universal (SSU):  Units of viscosity as measured by measured by observing the time in seconds required for 60 ml. Of a fluid to drain through a tubular orifice 0.483 inches long by 0.0695 inches in diameter at stated conditions of temperature and pressure. 

SCFD:  Standard cubic feet per day. 

SCFH:  Standard cubic feet per hour. 

SCFM:  Standard cubic feet per minute. 

Screen:  Covering for element for physical protection; also used as a basic material for a separator element or the basket in a basket strainer.  May have special coating such as Teflon. 

Screw Base:  Describes element base which is threaded to mounting by screwing the cartridge on the cartridge adaptor. 

Seal:  Any device which serves the purpose of sealing; examples are center seal gaskets, “O” rings, and mounting caps.  May also include two precision machined surfaces that seal, which is referred to as a metal to metal seal. 

Seal Nut:  A gasketed nut which holds element cap in place. 

Sedimentation,  Gravitational settling of particles suspended in a liquid.  Sometimes used in particle size analysis, since settling rate is a function of particle size.  See Stoke’s  law, terminal settling velocity. 

Selector Valve:  Component of a pressure gauge which permits independent pressure readings at two or three points. 

Self Cleaning:  Generally refers to a filtering device that is designed to clean itself by the use of a blowdown or backwash action.  Medium is commonly a screen mounted on a cylindrical drum or device that removes bulk solids from large flow rates.  Baffle in first stage aids in the separation of solids by impingement.  Blowdown may be continual or intermittent and operated either manually or automatically by instruments. 

Separation:  The action of separating solids or liquids from fluids. May be accomplished by impingement, filtration, or by coalescing.  The term “separation” is used in some circles when referring to the separation of liquids.  Also used to describe the action in the second stage of two stage separation. 

Separator/Filter:  Vessel which removes solids and entrained liquid from another liquid or gas.  Uses some combination of a baffle and/or coalescer, or separator element.  May be single stage, two stage, or single or two stage with prefilter section for gross solids removal.  Common application is the removal of water from gas or another immiscible liquid.  General reference to term implies the equipment is capable of both separation and filtration to specific degrees of efficiencies. 

Septum:  The porous material mounted on a plate or frame which separates the solids from the liquids in filtering.  Also referred to as filter cloth, filter medium, or filter plate. 

Service Life:  The length of time an element operates before reaching the maximum allowable pressure drop. 

Serviced:  Describes a vessel which has had old elements removed and replacement elements installed; servicing may also include installation of a new head gasket, repair of accessories, cleaning, etc. 

Shell:  Outer wall of a vessel.  Also referred to as body. 

Shredding,  A term used to describe the process when debris or particles show up in the effluent from a filter.  See fiber migration, media migration, unloading. 

Shute Wires:  Wires running the short way of the cloth as woven.  Often referred to as “fill” wires. 

Silica Gel:  A regenerated adsorbent, consisting of amorphous silica.  Used as a drying or dehumidifying agent for gases, liquids, or oils.  Also used in certain types of packaging where moisture may be a problem. 

Silicone, A class of rubber used for gaskets and “O” ring seals.  Also a class of lubricants widely used to lubricate machinery.  Silicone oil is commonly used to lubricate fibers or thread to make it slide easier.  Silicone lubricants are frequently used as a process aid when staple fiber is needled into felt products.  Silicone oils will ruin E-coat paint systems even when present at part per million levels. 

Silt Density Index,  An ASTM standard test, (ASTM D4189) for measuring the relative quantity of particulate matter in water.  The test uses 47 mm membranes and measures the decay in flow rate over a 15 minute period when water is filtered at a constant upstream pressure of 30 psi. 

Silting Index:  Measurement of the tendency of a fluid to cause silting in close tolerance devices as a result of fine particles and gelatinous materials being suspended in the fluid; measured by a silting index apparatus. 

Single Stage Separator/Filter:  Liquid or air/gas separator/filters containing only one type or kind of replaceable element, as opposed to two stage, three stage, or four stage separator/filters. 

Sintered:  Filter medium manufactured by the fusion of powdered, granular materials.  Sintering produces greater strength and density. 

Sisal:  A hard fiber obtained from the sword-like leaves of the sisal plant.  Agave sisalana.  The fibers are rather coarse but somewhat more flexible than henequen to which it is closely related.  It is white or creamy white in color, 24 to 70 inches in length, and very strong and durable.  It is cultivated commercially on large plantations in the State of Campeche, Mexico, in Haiti, East Africa, Java, and to a lesser extent in many other places.  It is used extensively in binder twine, also for summer rugs, brushes, etc.  Frequently called sisal hemp. 

Size Selectivity,  A measure of the ability of a separation process to separate particles according to size.  Filters with steep particles above the size of interest while allowing smaller particles to pass without plugging the filter. 

Skid Mounted:  Describes one or more vessels with pump and motor, all mounted on a portable platform. 

Slimes:  Slurry of fine solids; material to be filtered.  Also referred to as concentrate, feed, influent, intake, liquor, mud, prefilt, pulp, or sludge. 

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.  See article on how to dispose of Carbide Sludge. 

Slurry:  A thin, watery suspension; a material to be filtered. 

Soft Waste:  Waste from yarn manufacturing operations prior to spinning, and including some spinning waste.  It is waste without any twist, or with only the soft twist of a roving frame.  Almost all soft waste is reprocessed directly in the mill, and very little of it is offered for sale. 

Solids:  A mass contained in a stream which is considered undesirable and should be removed; that part of the discontinuous phase which is removed from liquid or gas through filtration. 

Soluble:  Capable of being dissolved in a fluid.  Opposite of insoluble. 

Solute:  The liquid which has passed through the filter.  Also referred to as discharge liquor, effluent, filtrate, mother liquor, or strong liquor. 

Solution:  A single phase combination of liquid and non-liquid substances, or two or more liquids.

Solvent:  Substance, usually a liquid, in which another substance becomes dissolved; the solvent will generally comprise the greater part of the solution. 

Space:  Area available to install a filter, separator/filter, or entrainment separator. 

Specific Gravity:  The ratio of weight of any volume of a substance to the weight of an equal volume of another substance.  Water for solids and liquids, and air or hydrogen for gases. 

Spectrophotometer:  A laboratory instrument which measures the wave length and intensity of light emitted by most chemical elements.  When a sample is atomized and burned, the presence of most elements may be determined by their spectra (wave length) emission down to the parts per million range. 

Spinning:  The operation of drafting roving to the required counts, inserting the required number of turns per inch in the yarn, and winding it into the form of a copy or onto a bobbin or spool.  Spinning is done on ring frames, mules, cap frames, or flyer frames.  Collectively, all of the operation in manufacturing a yarn from fibrous raw material.  The extrusion of a spinning solution through spinnerettes to form filaments.  Also describes a method of forming pressure vessel heads. 

Spore Forming Bacteria:   Bacteria which form a resting cell, difficult to destroy. 

Square Mesh (Wire Cloth):  Mesh count that is the same in both directions. 

Stack:  A term used to describe one or more cartridges mounted on a single column. 

Staple:  In natural fibers this expresses the length of a fiber of cotton, wool, flax, and the like.  In a synthetic, it signifies filaments that have been cut to the length of natural fibers. 

Static Generation:  Result of friction between two non-conductors such as filter or separators/filter elements and hydrocarbons and is retained in the liquid dielectric. 

Stoke’s Law:  A physical law which 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 just balances the gravitational acceleration, after which it will continue to fall at a constant velocity known as the terminal or free-settling velocity. 

Stool:  A device on the cartridge mounting plate used to mount an element.  Also called a cartridge adaptor. 

Stratification:  A condition in which the larger particles settle out below the finer ones.  Also referred to as classification. 

Stream:  A term sometimes used and synonymous with the words product, liquid, etc. in speaking of any matter processed by filtration or separation/filtration equipment. 

Strong Liquor:  The liquid which has passed through the filter.  Also referred to as discharge liquor, effluent, filtrate, mother liquor, or solute. 

Substrate:  Substance on which an enzyme or ferment acts; a basic material used in making filter media, usually in a deposit type process. 

Sump:  Collecting area of a vessel, located downstream from the coalescer elements, in which coalesced droplets of the dispersed phase are deposited; also called water leg.  May also be used to collect solids in applications where gross solids are present in a stream; also called a mud sump. 

Supernatant:  Liquid above settled solids. 

Surface:  That part of the media which is perpendicular to the direction of flow.  Also surface media which provide filtration, as opposed to media which may be considered depth media. 

Surface Energy:  A molecular reaction, the breaking away of ion particles from a mass. 

Surface Tension:   That property of liquids which tends to contract the exposed surface to the smallest possible area; I.e., cohesion between like molecules. 

Surfactants:  Coined expression for surface active agents which are sometimes called emulsifiers or wetting agents.  First appeared in hydrocarbons with the advent of the catalytic cracking process in refining.  Caused by the forming of sodium sulfonate and sodium napathanate molecules.  Affects liquid/ liquid separation by reducing interfacial tension and forming into a slime which blinds off the fibers used in coalescing media.

Surge:  The peak system pressure measured as a function of restricting or blocking fluid flow. 

Suspended Solids:  Non-settled particles in feed. 

Swarf,  The accumulation of contaminants generated from a grinding facility. 

Swing Bolt:  A type of vessel closure which reduces service time.  Opposite of thru-bolt flange where studs and nuts are used, such as with ASA type flanges. 

Synthetic machine coolant,  A man-made oil which emulsifies in water and is an alternative for natural oils from animal, vegetable or mineral sources. 



Temperature, Absolute:  The temperature measured from absolute zero which is minus 2730C., or minus 4600F. 

Tensiometer:  Device used to read the surface tension of a liquid, or to read the interfacial tension between two immiscible liquids. 

Terminal Pressure:  Pressure drop across the unit at the time system is shut down, or when the maximum allowable pressure drop is reached. 

Terminal Settling Velocity,  The steady velocity achieved by a falling particle when gravitational forces are balanced by viscious forces.  Terminal settling velocity is a function of particle size.  Some separation processes use this principle.  Large particles settle faster than small particles, all other things being equal. 

Thermal Relief:  Valve which is preset of effect opening when pressure becomes excessive due to increased atmospheric temperature. 

Thermoswitch:  Control which is preset to start and stop immersion heater operation at certain temperatures. 

Thixotropic,  A flow characteristic of certain solutions and suspensions whose viscosity is reduced by stirring, shearing, or pressure.  The opposite of dilatant. 

Three Stage Separator/Filters:  Liquid prefilter/ coalescer/ separators containing three kinds or types of replaceable elements.  Air/ gas separator/ filters containing two kinds of replaceable elements in addition to a first stage baffle.  As opposed to single, two, or four stage separator/ filters. 

Thru-Bolt:  A type of vessel closure using studs and nuts. 

Time-to-cleanup, A term used to describe how long it takes for the effluent from a fresh filter to reach a stated level of cleanliness at a stated flow.  This is one measure of how clean the filter is and how long it takes for residual manufacturing debris to work its way out of the filter.  This test is used in the electronics industry to evaluate filters for critical applications. 

Titration:  A method of analyzing a solution by adding another solution until a given reaction is produced. 

Tortuous Path:  Crooked, twisting, or winding path which tends to trap or stop solid particulate matter. 

Total Suspended Solids (TSS),  The concentration of suspended particles per unit volume in a fluid.  This term is sometimes used to prevent confusion with measurements that include dissolved solids. 

Toxic:  Having a poisonous effect. 

Tramp OilAny foreign undesirable oil, grease or floating contaminants found in a water base machine coolant. 

Tube:  Either center tube or cartridge mounting tube.  Sometimes used to describe a wound cartridge or glass fibers formed into a cylinder with an open center. 

Tube Sheet:  A cartridge mounting plate. 

Turbidity,  A condition describing a hazy or cloudy fluid.  See NTU, nephelometer. 

Turbulent Flow,  A flow regime characterized by high Reynolds numbers and high drag forces on the surfaces the fluid flows past.  Turbulent flow is characterized by internal agitation and flow lines that are not parallel to the pipe or duct.  Turbulent flow helps keep solids in suspension.  The opposite of laminar flow. 

Twist:  The turns about its axis; per unit of length, observed in a fiber, roving, yarn, cord, etc.  Twist is usually expressed as turns per inch, T.P.I. Term sometimes applied to warp yarn to distinguish it from filling yarn.  Silk sewing thread; e.g. buttonhole twist. 

Twisting:  The process of combining two or more ends into a ply yarn or cord.  Yarns are twisted to obtain greater strength and smoothness, increased uniformity, or to obtain novelty effects. 

Two Stage Separator / Filters:  Liquid separator / filters and prefilter / coalescers containing two kinds or types of replaceable elements.  Air / gas separator / filters containing one kind or type of replacement element in addition to a first stage baffle.  As opposed to single stage, three stage, or four stage separator / filters.  Two stage are considered the most efficient device to separate immiscible liquids.  See separator / filters or separation. 



Ultrafiltration:  Separation of colloidal solids from liquids through semi permeable media. 

Ultraviolet Sterilization,  A technique used to prevent the growth of microbes in pure water.  Ultraviolet light is effective at killing microbes and it doesn’t change the purity or chemistry of water. 

Uniformity Of Feed:  Uniformity of the mixture of the solids in the feed liquid. 

Underflow,  The liquid discharging from the bottom of a hydroclone which has the concentrated contaminants separated by the hydroclone.  Also, flow drawn from the bottom of a tank. 

Unloading:  Release downstream of trapped contaminate; due to change in flow rate, mechanical shock and vibration, or as excessive pressure builds up; or media failure. 

Upstream:  Portion of the product stream which has not yet entered the system.   



Vapor:  A solid or a liquid in a gaseous form under normal conditions of pressure and temperature. 

Vegetable Fiber:  A paper-like gasket material. 

Velocity:  The time rate of motion in a given direction and sense.

Viscosity:  Degree of fluidity; property of fluids’ molecular structure by virtue of which they resist flow.  The resistance to flow exhibited by a liquid resulting from the combined effects of cohesion and adhesion.  The units of measurement are the poise and the stoke.  A liquid has a viscosity of one poise if a force of one dyne per square centimeter in area and one centimeter apart to move past one another at a rate of the time of flow or movement of a ball, ring, or other object in specially shaped or sized apparatus. 

Viscosity Index:  A numerical value assigned to a lubricating oil which indicates to what degree the oil changes in viscosity with change in temperature.  Higher (VI) Viscosity Index Oils show the least change. 

Viton A:  A trade name for a material used in gaskets and “O” rings.

Void Channels:  The open passages of the medium through which the liquid travels. 

Void Restriction:  Obstructions in the void openings which interfere with flow. 

Voids:  The opening in the medium.  Also referred to as interstices or pores. 

Volumetric Flow Rate:  Fluid flow expressed as a volume flowing per unit of time 



Waffle Weave:  Pattern of these fabrics resembles the cellular comb of the honey bee; is used for drainage cloths beneath the regular filter cloth.  Also called honeycomb weave. 

Waste:  Material removed, rejected, or otherwise lost in various manufacturing processes.  

Water Leg:  Area of vessel for collection of water.  Also called a sump. 

Water Wettable:  Capable of accepting water, or being hydrophilic; opposite of repellency. 

Weight Of Solids:  A measure of solid particulate matter contained in a fluid sample.  May be reported in various units such as milligrams per liter, weight percent, pounds per barrel, etc. 

Wet Strength:  The strength of the medium when saturated with water.  It can also refer to the property obtained when an additive is imparted to a filter paper to give it additional strength when wet. 

Wetted:  Having accepted water or other liquid. 

Wound:  Name for filter elements constructed of fibers wound around a center core. 

Woven:  Term given filter materials which are formed by weaving, much the same as for fabrics or textiles. 



Yarn:  A generic term for an assemblage of fibers or filaments, either natural or manufactured, twisted or laid together so as to form a continuous strand which can be used in weaving, knitting, or otherwise made into a textile material. 

Yoke:  End cap used to hold a cartridge in place.