Glossary of Terms

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  • Ablation
    Process of removal by erosion, melting, evaporation, or vaporization.
  • Abrasion
    A wearing, grinding or rubbing away by friction, usually (but not always) involving the action of particles against or between surfaces.
  • Absolute (Dynamic) Viscosity
    The ratio of shear stress to shear rate, representing a fluid's internal resistance to flow. Although the fundamental unit of absolute or dynamic viscosity is the poise, results are often expressed in centipoise (cP). 1 centipoise equals .01 poise.
  • Absorption
    The process by which one substance draws itself into another substance. An example is a sponge picking up water, or on oil recovering gasoline from wet natural gas
  • Accumulator
    An in-line vessel that stores fluid under pressure for later release; used in some larger hydraulic systems.
  • Accuracy
    The closeness of a measured result to the actual (true) value.
  • Acid
    any one of various hydrogen-containing molecules or ions capable of giving up a proton to a base, of accepting an unshared pair of electrons from a base, or of reacting with a base to form a salt. A more limited definition restricts the acid to a hydrogen-containing substance that contains a(...)
  • Acid digestion
    process of dissolving a sample in an acid matrix, usually accompanied by heating.
  • Acid Treating
    A refining process where unfinished petroleum products (gasoline, kerosene, lube oil stocks, etc.) are brought into contact with sulfuric acid to improve their color, odor, and other properties.
  • Acidity
    Specific to oil analysis, acidity denotes the presence of weakly and strongly acidic materials whose total concentration is usually defined in terms of the TAN (Total Acid Number).
  • Active metal
    A metal ready to corrode, or being corroded. Contrast with noble metal.
  • Additives
    An agent added to oils, fuels, and coolants to impart specific beneficial properties to the finished products. Additives create new fluid properties, enhance properties already present and reduce the rate at which undesirable changes take place in a fluid during service. Selected additives(...)
  • Adhesion
    the force of molecular attraction exerted between two surfaces in contact.
  • Adsorption
    the adhesion of an extremely thin layer of molecules (gases, dissolved solids, or liquids) to the surfaces of solids or liquids with which the molecules are in contact. This process is utilized in a broad range of fluid and additive applications to concentrate one material on the surface of another
  • Aeration
    combining or charging a fluid with a gas, as in oil being aerated with air
  • Aerosol
    a highly dispersed suspension of fine solid or liquid particles in a gas.
  • Aftercooling
    the process of cooling compressed gases under constant pressure after the final stage of compression.
  • Agglomeration
    the action of combining a number of small particles into a larger single mass, often the operating principle for additives which promote particle attraction and clumping.
  • Air entrainment
    The incorporation of air (bubbles) as a dispersed phase in a liquid. Air entrainment may result from mechanical means or by sudden environmental changes. The presence of entrained air is usually obvious from the hazy, opaque, or bubbly physical appearance of the liquid while dissolved air can(...)
  • Alkali
    any substance having basic (as opposed to acidic) properties. A more limited definition restricts the alkali to hydroxides of ammonium, lithium, potassium and sodium.
  • Alloy steel
    steel containing specified quantities of alloying elements added to effect changes in mechanical or physical properties.
  • Ambient temperature
    temperature of the area or atmosphere around a process, (not the operating temperature of the process itself).
  • Anhydrous
    free of water, especially water of crystallization (water present as an internal part of the structure of a salt crystal).
  • Aniline point
    the minimum temperature for complete miscibility of equal volumes of aniline and the sample. A product of high aniline point will be Iow in aromatics and naphthenes and, therefore, high in paraffins. Aniline point is often specified for spray oils, cleaning solvents, and thinners, where(...)
  • Annealing
    a generic term denoting a treatment consisting of heating a metal to a suitable temperature and holding it there, followed by cooling at a suitable rate. This process is used primarily to soften metallic materials, but also to simultaneously produce desired changes in the metal’s(...)
  • Anodizing
    forming a conversion coating on a metal surface by anodic (electron-removing) oxidation; most frequently applied to aluminum.
  • API base stock
    base fluid for automotive engine oils. The API (American Petroleum Institute) currently designates five classes of base stocks. These stock types are independent of crude source or processing. Instead, they are based on physical characteristics of the base stock, which are then related to(...)
  • API engine service categories
    gasoline and diesel engine oil quality levels established jointly by API, SAE, and ASTM, and sometimes called SAE or API/SAE categories; formerly called API Engine Service Classifications.
  • API gravity
    a gravity scale established by the American Petroleum Institute and in general use in the petroleum industry, the unit being called "the API degree", which is represented by the equation:API gravity, deg = (141.5/specific gravity at 60/60ºF)-131.5
  • Apparent viscosity
    the ratio of shear stress to rate of shear of a non-Newtonian fluid such as lubricating grease, calculated from Poiseuille's equation and measured in poises. The apparent viscosity changes with changing rates of shear and temperature and must, therefore, be reported as the value at a given(...)
  • Aromatic
    derived from, or characterized by, the presence of the benzene ring.
  • Ash
    a measure of the amount of inorganic material in lubricating oil. Determined by burning the oil and weighing the residue.
  • Asperities
    microscopic projections on metal surfaces. Asperities result from normal finishing processes or from any other process or condition which changes the surface profile. Interference between opposing asperities in sliding or rolling wear is a source of friction, and can lead to metal welding and(...)
  • Auto-ignition point
    the temperature at which a substance ignites without other sources of energy. Also, associated with the spontaneous ignition and sustained combustion of part or all of the fuel-air mixture in an engine. The flame speed is many times greater than that associated with normal spark ignition,(...)
  • Babbitt
    a soft, white, non-ferrous alloy of copper, antimony, tin and lead. Found in sleeve/journal bearing overlays.
  • Bactericide
    chemical agent that inhibits the growth of bacteria promoted by the presence of water.
  • Bactericide
    chemical agent that inhibits the growth of bacteria promoted by the presence of water.
  • Base
    a material that neutralizes acids. Also, term referring to an oil additive containing colloidally dispersed metal carbonate, used to reduce corrosive wear.
  • Base stock
    a primary refined petroleum fraction or a selected synthetic material, into which additives are blended to produce finished lubricants.
  • Batch
    quantity of product resulting from a single blending or other processing operation.
  • Bearing
    a machine part which positions and supports load and movement through the action of fitted or formed surfaces that move with respect to each other by sliding, rolling, reciprocating, or by combinations of these motions. Selected bearing types are: Rolling element bearingsDeep groove(...)
  • Beta Rating
    efficiency-based filter performance rating. This is done using the Multi-Pass Test which counts the number of particles of a given size before and after fluid passes through a filter, over multiple passes of the fluid through the filter being tested.
  • Beta ratio (ß-ratio)
    the ratio of the number of particles greater than a given size entering a filter to the number of particles greater than the same size leaving the filter, under specified test conditions.
  • Black oils
    lubricants containing asphaltic materials, which impart extra adhesiveness, that are used for open gears and steel cables.
  • Blend(ing)
    omposite of two or more components or lubricants for the purpose of obtaining the desired physical and/or chemical properties. In petroleum product manufacture, a blend may consist of two or more basestocks or a basestock combined with chemical additives.
  • Bloom
    rapid growth and spread of a bacterial or algal colony. Also, fluorescence; the color of an oil by reflected light that could differ from its color by transmitted light.
  • Blow-by
    passage of unburned fuel and combustion gases past the piston rings of internal combustion engines, resulting in fuel dilution and contamination of the crankcase oil.
  • Boiling point
    rthe temperature at which a substance boils, or is converted into vapor by bubbles forming within the liquid; it varies with pressure.
  • Bottoms
    in refining, the high-boiling point residual liquid that collects at the bottom of a distillation column, such as a pipe still. Examples of bottoms include such components as heavy fuels and asphalts.
  • Boundary lubrication
    the state of lubrication when conditions exist that do not permit the formation of a lubricant film capable of completely separating the moving parts. Under these conditions, additives are used to increase oil film strength or coat metal surfaces with a sacrificial 'anti-wear' film. Anti-wear(...)
  • Brinelling
    tpermanent deformation of the bearing surfaces where the rollers (or balls) contact the races. Brinelling results from excessive load or impact on stationary bearings. It is a form of mechanical damage in which metal is displaced or upset without being permanently removed from the surface.
  • Brookfield viscosity
    apparent viscosity in cP (centipoise) determined by Brookfield viscometer, which measures the torque required to rotate a spindle at constant speed in oil of a given temperature. Basis for measuring low temperature viscosity of lubricants.
  • BS&W (bottom sediment and water)
    the material that collects in the bottom of storage tanks, usually composed of oil, water, and foreign matter. Also called bottoms, or bottom settling and water.
  • BTU
    British thermal unit. The amount of heat required to raise the temperature of 1 pound of water 1 degree Fahrenheit.
  • Bubble point
    the differential (inner vs. outer) gas pressure at which the first steady stream of gas bubbles is emitted from a wetted filter element under specified test conditions.
  • Burst pressure rating
    maximum specified differential pressure that can be applied to a filter element without outward structural or filter-medium failure.
  • Bushing
    a usually removable cylindrical lining for an opening used to limit the size of the opening, resist abrasion, or serve as a guide.
  • Bypass filtration
    filtration approach in which only part of the total flow of a circulating fluid system passes through a filter at any given time, or approach in which a separate pump and filter combination operates in parallel to the main flow.
  • Bypass valve
    differential pressure valve or fitting on a filter which opens when the filter reaches a preset maximum capacity, assuring continued flow by allowing part or all of the fluid to bypass the filter element.
  • Calibration / standardization
    These two terms have a broad or narrow definition, depending on circumstances, and some sources use them interchangably. Calibration connotes extensive or exacting measurements, under specified conditions, to determine how closely the output values of a measuring process or system compare to(...)
  • Cam
    a rotating or sliding eccentric part which passes motion to a roller or pin moving against its edge. Used to cyclically raise, lower, or otherwise move a part a specific distance, such as the action of a cam moving an engine's valves.
  • Capacity
    the measure of total content, production or output. For example, the amount of heat a burned fuel will release, or amount of contaminants a filter will hold before an excessive pressure drop is caused.
  • Capillarity
    a property of a solid-liquid system manifested by the tendency of the liquid in contact with the solid to rise above or fall below the level of the surrounding liquid; this phenomenon is seen in a smallbore (capillary) tube.
  • Capillary viscometer
    a viscometer in that the oil flows through a capillary tube.
  • Carbon
    a non-metallic element, number 6 in the periodic table, found in the native (uncombined) form as graphite or diamond. Carbon is a constituent of all organic compounds including coal, petroleum, asphalt, etc. It also occurs in combined form in many inorganic substances; i.e., carbon dioxide,(...)
  • Carbon residue
    coked material remaining after an oil has been exposed to high temperatures under controlled conditions.
  • Case drain filter
    a filter located in a line conducting fluid from a pump or motor housing to reservoir.
  • Catalyst
    a substance which speeds a chemical action without undergoing a chemical change itself during the process.
  • Catalytic converter
    an integral part of vehicle emission control systems since 1975. Oxidizing converters remove hydrocarbons and carbon monoxide (CO) from exhaust gases, while reducing converters control nitrogen oxide (NOx) emissions. Both use noble metal (platinum, palladium or rhodium) catalysts that can be(...)
  • Catastrophic failure
    sudden, unexpected failure of a system.
  • Cavitation
    the formation and instantaneous collapse of innumerable air or vapor pockets (or bubbles) in flowing liquids due to the hydrodynamic generation of rapid and intense pressure changes. This may result from the movement of a solid body, such as a propeller blade or piston. Cavitation can also(...)
  • Cavitation damage
    the degradation of a solid body resulting from its exposure to cavitation. This may include loss of material, surface deformation or changes in properties or appearance.
  • Cellulose media
    a filter material made from plant fibers. Because cellulose is a natural material, its fibers are rough in texture and vary in size and shape. Compared to synthetic media, these characteristics create a higher restriction to the flow of fluids.
  • Centipoise (cP)
    a standard reporting unit of absolute viscosity. 1 centipoise = 0.01 poise.
  • Centistoke (cSt)
    a standard reporting unit of kinematic viscosity. 1 centistoke = 0.01 stoke.
  • Centralized lubrication
    a system of lubrication in which a metered amount of lubricant or lubricants for the bearing surfaces of a machine or group of machines are supplied from a central location.
  • Centrifugal separator
    a separator that removes immiscible fluid and solid contaminants that have a different specific gravity than the fluid being purified by accelerating the fluid mechanically in a circular path and using the radial acceleration component to isolate these contaminants.
  • Certificate of analysis
    list of laboratory test results that the supplier affirms to be representative of the quality of a product shipped to a particular customer.
  • Cetane improver
    a substance which, when added to a diesel fuel, has the effect of increasing its cetane number. In this class are nitro alkanes, nitrates, nitro carbonates, and peroxides.
  • Cetane index
    an approximation of cetane number based on API gravity and mid-boiling point of a fuel.
  • Cetane number (calculated)
    the cetane number of distillate fuels as estimated from the API gravity and mid-boiling point by using a formula. This estimate is used if a standard test engine is not available, or if the sample is too small for an engine test.
  • Channeling
    the phenomenon observed among gear lubricants and greases when they thicken, due to cold weather or other causes, to such an extent that a groove is formed through which the part to be lubricated moves without actually coming in full contact with the lubricant.
  • Chip detector
    a magnetic plug fitted with open electrical contacts. When one or more ferromagnetic particles are attracted to the detector end and bridge the contacts, this completes an electrical circuit and activates an indicator, thus notifying the operator that this particle buildup has occurred. Often(...)
  • Chromatography
    a method of separation based on selective adsorption. A solution of the substance is allowed to diffuse slowly through a column of adsorbent, moved by a gas or solvent flow. Different substances will pass with different speeds down the column and will eventually be separated into zones whose(...)
  • Circulating lubrication
    lubricating system that recirculates fluid through a system after it has passed through the system and returned to a central collection point.
  • Clean room
    an enclosed area in which air quality factors (such as particulate level, temperature, humidity, and pressure) are controlled and maintained at specific levels by special facilities and operating processes.
  • Cleanable filter
    a filter element whose media allows cleaning for reuse, using a suitable process to restore an acceptable percentage of the filter's original contaminant capacity.
  • Cloud point
    the temperature at which paraffin waxes or other solid substances begin to crystallize or separate from the solution, imparting a cloudy appearance to the oil when chilled.
  • Coalescer
    a separator that divides a mixture or emulsion of two immiscible liquids using the interfacial tension between the two liquids and the difference in wetting of the two liquids on a particular porous medium.
  • Coefficient of friction
    the number obtained by dividing the friction force resisting motion between two bodies by the normal force pressing the bodies together.
  • Cohesion
    molecular attraction that causes substances to resist mechanical separation.
  • Cold cranking simulator (CCS)
    an intermediate shear rate viscometer that predicts the ability of an oil to permit a satisfactory engine cranking speed under cold conditions.
  • Collapse
    an inward structural failure. For example, filter element failure due to abnormally high differential pressure.
  • Collapse pressure
    the minimum differential pressure that an element is designed to withstand without permanent deformation.
  • Colloid
    a suspension of finely divided particles in a gas or liquid which do not settle and are not easily filtered. A lubricating grease is a colloidal system, in which metallic soaps or other thickening agents are dispersed in, and give structure to, the liquid lubricant.
  • Complex grease
    a lubricating grease thickened by a complex soap consisting of a normal soap and a complexing agent.
  • Compound
    a distinct substance formed by the combination of two or more elements in definite proportions by weight and possessing physical and chemical properties different from those of the combining elements.
  • Compounding
    the addition of fatty oils and similar materials to lubricants to impart special properties. Lubricating oils to which such materials have been added are known as compounded oils.
  • Compressibility
    the change in volume of a unit volume of a fluid when subjected to a unit change of pressure.
  • Compression
    the use of mechanical force and motion to pressurize (apply force to) a gas or liquid. Examples of pressure-creating devices are compressors, where the pressure of a gas is raised, and pumps, which are more commonly associated with liquids.
  • Compression ratio
    in an internal combustion engine, the ratio of the volume of combustion space at bottom dead center to that at top dead center.
  • Consistency
    the degree to that a semisolid material such as grease resists deformation. Sometimes used qualitatively to denote viscosity of liquids.
  • Contaminant
    any foreign or unwanted substance that can have a negative effect on system operation, life or reliability.
  • Contaminant capacity
    the weight of a specified artificial contaminant entering a filter to produce a given differential pressure across a filter at specified conditions. Used as an indication of relative service life.
  • Contaminant failure
    any loss of performance due to the presence of contamination. This process may occur gradually or rapidly, depending on conditions.
  • Contaminant lock
    the binding or jam of a moving part caused by solid contaminant accumulation between critical surfaces.
  • Contamination control
    a broad subject that applies to all types of material systems (including both biological and engineering). It is concerned with planning, organizing, managing, and implementing all activities required to determine, achieve and maintain a specified contamination level.
  • Coolant
    a fluid used to remove heat. This term has broad application in any process which generates heat as a result of frictional or combustion processes.
  • Coolant
    a fluid used to remove heat. This term has broad application in any process which generates heat as a result of frictional or combustion processes.
  • Copper strip corrosion
    a test that assesses a petroleum product’s tendency to corrode pure copper.
  • Correlation
    two or more things so related that the presence or amount of one corresponds to the presence or amount of another. For example, the percentage of peaks in a used oil infrared spectrum which match those in a new reference oil. A high correlation would imply the oils match, a low correlation(...)
  • Corrosion
    the decay and loss of a metal due to a chemical reaction between the metal and its environment. It is a transformation process in which the metal passes from its elemental form to a combined (or compound) form.
  • Coupling
    a connecting assembly, as in a joining connector for hoses or pipes.
  • Cracking
    the process whereby large molecules are broken down by the application of heat and pressure to form smaller molecules.
  • Crown
    the top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.
  • Cryogenics
    the branch of physics relating to the production and effects of very low temperatures.
  • Cutting fluid
    any fluid that assists the cutting operation by cooling or lubricating the cutting tool or the material being cut.
  • Cycle
    a single complete operation consisting of progressive phases starting and ending at the neutral position.
  • Cyclic stress
    a stress whose magnitude fluctuates in a regular pattern.
  • Cylinder
    a device that converts fluid power into linear mechanical force and motion. It usually consists of a moveable element such as a piston and piston rod, plunger rod, plunger or ram, operating with in a cylindrical bore.
  • Deaerator
    a separator that removes air from the system fluid.
  • Defect
    an imperfection in a material that contributes significantly to failure or limited serviceability.
  • Degas
    removing air from a liquid, usually by ultrasonic and/or vacuum methods.
  • Degradation
    the progressive reduction of performance, usually ending in failure of a machine or lubricant.
  • Dehydrator
    a separator that removes water from the system fluid.
  • Delamination
    a complex wear process where a machine surface is peeled away or otherwise removed by forces of another surface acting on it in a sliding motion.
  • Demulsibility
    the ability of a fluid that is insoluble in water to separate from water with which it may be mixed in the form of an emulsion.
  • Density
    the mass of a unit volume of a substance. Its numerical value varies with the units used.
  • Deposit
    process of a solid residue accumulating on a surface. For example, oil-insoluble materials that result from oxidation and decomposition of lube oil and contamination from external sources and engine blow-by are deposited on machine or engine parts. Other examples are sludge, varnish, lacquer(...)
  • Depth filter
    a filter medium that retains contaminants primarily within the winding deep structure of the filter.
  • Desorption
    opposite of absorption or adsorption. In filtration, it relates to the downstream release of particles previously retained by the filter.
  • Detection limit
    practically defined as the point where the signal level decreases to less than two to three times the noise level.
  • Detergent
    in lubrication, either an additive or a compounded lubricant having the property of keeping insoluble matter in suspension thus preventing its deposition where it would be harmful. A detergent may also redisperse deposits already formed.
  • Dielectric Strength
    a measure of the ability of an insulating material to withstand electric stress (voltage) without failure. Fluids with high dielectric strength (usually expressed in volts or kilovolts) are good electrical insulators.
  • Dieseling
    the continued running of a spark-ignited engine after the ignition is turned off. There are two basic causes of dieseling: surface ignitionwhere combustion chamber surfaces remain hot enough to ignite fuel after the spark is terminated. compression ignitionwhere the conditions of(...)
  • Differential pressure indicator
    an indicator that signals the difference in pressure between any two points of a system or a component.
  • Disposable
    a filter element intended to be discarded and replaced after one service cycle.
  • Dissolved gases
    those gases that enter into chemical solution with a fluid, as distinguished from free or entrained gases (mechanically mixed but not chemically bound).
  • Distillation
    process of driving gas or vapor from liquids or solids by heating, then condensing the vapor for the purposes of separation, purification, or measurement.
  • Dry-film lubricant
    solid material deliberately deposited between two moving surfaces to prevent metal-to-metal contact, thus reducing friction and wear. Such materials are especially useful in the region of boundary lubrication, and for lubrication under special conditions of extremely high or low temperature(...)
  • Duplex filter
    an assembly of two filters with valving for selection of either or both filters.
  • Effluent
    material exiting a system.
  • Elastohydrodynamic lubrication
    Lubrication modified to take into consideration the elastic properties of the bearing material and the viscosity increase of the lubricant under concentrated load. In rolling element bearings, the bearing undergoes elastic deformation (flattening) as it rolls under load in the bearing race.(...)
  • Electrostatic separator
    a separator that removes contaminant from dielectric fluids by applying an electrical charge to the. Once charged, the contaminant is then attracted to a collection device of different electrical charge.
  • Emulsibility
    the ability of a non-water-soluble fluid to form an emulsion with water.
  • Emulsion
    intimate mixture of oil and water, generally of a milky or cloudy appearance. Emulsions may be of two types: oil-in water (where water is the continuous phase) and water-in-oil (where water is the discontinuous phase).
  • Environmental contaminant
    material entering a system from an operating system's external surroundings, such as dust, air, moisture or chemicals.
  • Erosion
    the progressive removal of a machine surface by cavitation or by particle impingement at high velocities.
  • Failure
    a general term used to imply that a part or system has:Become completely inoperable;Is still operable but is incapable of satisfactorily performing its intended function;Has deteriorated seriously to the point that it has become unreliable or unsafe for continued use.
  • Fatigue
    a structural failure due to flexing caused by cyclic motions or cyclic differential pressures which do not exceed the tensile strength of the material.
  • Fault
    failure to reach or maintain a measured standard of reliability or performance. With respect to condition monitoring, additional terms relating to fault are: OccurrenceAny detected or diagnosed fault requiring remedial action whether the action was reactive, preventive or proactive Apparent(...)
  • Ferrography
    a method of debris analysis that uses a high gradient magnetic field to attract, hold and deposit particles contained in a fluid. The resulting slide traps both magnetic and non-magnetic particles, which are then microscopically examined for characteristics that reveal size, composition, mode(...)
  • Film strength
    the property of an oil which enables it to maintain an unbroken film on lubricated surfaces under operating conditions, where otherwise there would be scuffing or scoring of the surfaces.
  • Filter
    any device or porous substance used as a strainer for cleaning fluids by removing suspended matter.
  • Filter efficiency
    method of expressing a filter's ability to trap and retain contaminants of a given size.
  • Filter element
    the porous device that performs the actual process of filtration.
  • Filter head
    an end closure for the filter case or bowl that contains one or more ports.
  • Filter housing
    a ported enclosure that directs the flow of fluid through the filter element.
  • Filter life test
    a type of filter capacity test in which a clogging contaminant is added to the influent of a filter, under specified test conditions, to produce a given rise in pressure drop across the filter or until a specified reduction of flow is reached. Filter life may be expressed as test time required(...)
  • Filter media, depth
    porous materials that primarily retain contaminants within a tortuous path, performing the actual process of filtration.
  • Filter media, surface
    porous materials which primarily retain contaminants on the influent face, performing the actual process of filtration.
  • Filtration
    the physical or mechanical process of separating insoluble particulate matter from a fluid by passing the fluid through a filter medium that traps the insoluble particles.
  • Fire point
    the temperature at which vapor released from a combustible liquid will burn continuously when ignited under specified conditions.
  • Fire-resistant fluid
    a fluid difficult to ignite and/or which shows little tendency to propagate flame, used especially in high-temperature or hazardous hydraulic applications. These fluids are less flammable than mineral (petroleum) oil and are approved for fire resistancy by Factory Mutual Research. They will(...)
  • Flash point
    the lowest temperature at which vapors arising from the oil will ignite momentarily when exposed to a flame.
  • Flaw
    an imperfection in a material that does not affect its serviceability. A component may have imperfections and still retain its usefulness. This fact is recognized by most material codes that permit, but limit, the size and extent of imperfections.
  • Flow fatigue rating
    the ability of a filter element to resist structural failure of the filter medium due to flexing caused by cyclic differential pressure.
  • Flow, laminar
    fluid flow in parallel layers.
  • Flow rate
    the volume, mass, or weight of a fluid passing through any conductor per unit of time.
  • Flow, turbulent
    fluid flow in random directions.
  • Flowmeter
    a device which indicates either flow rate, total flow, or a combination of both.
  • Fluid
    a general classification of physical state, including liquids and gases.
  • Fluid compatibility
    assessment of a fluid mixture or one or more of its components to avoid or control undue effects on fluid properties, filters, seals or the system serviced with the mixture.
  • Fluid power
    energy transmitted and controlled through use of a pressurized fluid.
  • Flushing
    a fluid circulation process designed to remove contamination from the wetted surfaces of a fluid system.
  • Foam
    an agglomeration of gas bubbles separated from each other by a thin liquid film, which is observed as a persistent phenomenon on the surface of a liquid.
  • Force feed lubrication
    pressurized lubrication system delivering oil directly to the lubricated parts.
  • Fourier Transform
    a mathematical technique for analysing a complex waveform into its component frequencies and thus expressing it as a sum of a continuous series of sine and cosine (fixed frequency and amplitude) waves. The Fourier transform is central to many kinds of signal processing, including the analysis(...)
  • Fretting corrosion
    surface oxidation resulting when two metals are held in contact and subjected to repeated small sliding, relative motions. Also termed brinelling or chafing.
  • Friction
    the resisting force encountered at the common boundary between two bodies when, under the action of an external force, one body, moves or tends to move relative to the surface of the other.
  • Full-flow filtration
    a system of filtration in which the total flow of a circulating fluid system passes through a filter.
  • Full fluid-film lubrication
    a continuous lubricating film thick enough to completely separate two surfaces. Normally in full fluid-film lubrication oil adheres to the moving part and is drawn into the area between the sliding surfaces, where hydrodynamic processes form a pressure wedge.
  • Gasohol
    a blend of 10% anhydrous ethanol (ethyl alcohol) and 90% gasoline, by volume. Used as a motor fuel.
  • Gauge
    an instrument or device for measuring, indicating or comparing a physical characteristic.
  • Gear
    a cylindrical or conical part using a tooth or screw-based surface configuration to mechanically transmit power from one portion of a machine to another. Gear designs are based in part on the shaft alignment: parallel, angled, over-and-under, etc. Selected gear types are: Spur gearHas teeth(...)
  • Gear train
    group or sequence of gears which perform a desired mechanical transfer of power. Selected gear train types are: TransmissionGear train characterized by multiple selectable gear speed ratios and the ability to uncouple the gear train from the power source to permit starting and stopping the(...)
  • Generated contaminant
    created by internal processes such as wear or progressive degradation of system fluids, rather than external sources or inherent from assembly or maintenance.
  • Graphite
    a crystalline form of carbon having a laminar structure, which is used as a lubricant. It may be of natural or synthetic origin.
  • Gravimetric analysis analysis
    a method of analysis whereby the dry weight of contaminant per unit volume of fluid can be measured showing the degree of contamination in terms of milligrams of contaminant per liter of fluid.
  • Grease
    a lubricant composed of an oil or oils thickened with a soap, soaps or other thickener to a semisolid or solid consistency.
  • Hardness
    the resistance of a substance to surface abrasion.
  • Heat exchanger
    device which transfers heat through a conducting wall from one fluid to another.
  • Housing
    a ported enclosure which directs the flow of fluid through the filter element.
  • Hydraulic Fluid
    fluid serving as the power transmission medium in a hydraulic system, with specific properties tailored to the fluid's use in this application.
  • Hydraulics
    engineering science pertaining to liquid pressure and flow.
  • Hydrocarbon
    a compound containing only hydrogen and carbon. The simplest hydrocarbons are gases at ordinary temperatures; but with increasing molecular weight, they change to the liquid form and, finally, to the solid state. They form the principal constituents of petroleum.
  • Hydrodynamic lubrication
    a system of lubrication in which the shape and relative motion of the moving surfaces causes the formation of a fluid film having sufficient pressure to separate the surfaces.
  • Hydrofinishing
    a process for treating raw extracted base stocks with hydrogen to saturate them for improved stability.
  • Hydrolysis
    breakdown process that occurs in anhydrous hydraulic fluids as a result of heat, water, and metal catalysts (iron, steel, copper, etc.)
  • Hydrolytic stability
    ability of additives and certain synthetic lubricants to resist chemical decomposition (hydrolysis) in the presence of water.
  • Hydrometer
    an instrument for determining either the specific gravity of a liquid or the API gravity.
  • Hydrostatic lubrication
    a system of lubrication in which the lubricant is supplied under sufficient external pressure to separate the opposing surfaces by a fluid film.
  • Hypoid gear lubricant
    a gear lubricant especially designed for hypoid gear types, as in the differential of an automobile. Hypoid gear tooth contact involves a combination of radial and sideways sliding which is intermediate between the worm type and the spiral bevel type gear, requiring additional EP (extreme(...)
  • Idler
    a wheel, gear or roller inserted into a drive train primarily for the function of guiding, supporting or tensioning a portion of the drive train.
  • Immiscible
    incapable of being mixed without separation of phases. Water and petroleum oil are immiscible under most conditions, although they can be made miscible with the addition of an emulsifier.
  • In-line filter
    a filter assembly in which the filter element is mounted along the same orientation as the filter inlet and outlet.
  • Indicator
    a device which provides external evidence of sensed phenomena.
  • Indicator, differential pressure
    n indicator that signals the difference in pressure between two points, typically between the upstream and downstream sides of a filter element.
  • Influent
    the material entering a system.
  • Infrared spectra
    a graph of infrared energy absorbed at various frequencies in the additive region of the infrared spectrum. The current sample, the reference oil and the previous samples are usually compared.
  • Ingested contaminants
    environmental contaminant that enters a system due to the action of the system or machine.
  • Inhibitor
    any substance that slows or prevents such chemical reactions as corrosion or oxidation.
  • Insolubles
    residues of carbon or agglomerates of carbon and other material such as spent additives or oxidation by-products.
  • Interfacial tension (IFT)
    the energy per unit area present at the boundary of two immiscible liquids, usually expressed in dynes/cm.
  • ISO Solid Contaminant Code
    a index number code assigned on the basis of the number of particles per unit volume, allowing quick assessment of contamination.
  • ISO viscosity grade
    a number indicating the nominal viscosity of an industrial fluid lubricant at 40°C (104°F) as defined by ISO Standard 3448. For example, an unused ISO 68 grade product would be expected to show a viscosity at 40°C of 68 cSt, plus or minus 10% (6.8 cSt). This pattern is maintained throughout(...)
  • Kinematic viscosity
    the ratio of the absolute viscosity to the density at the temperature of the viscosity measurement. The metric units of kinematic viscosity are the stoke and centistoke, which correspond to the poise and centipoise of absolute viscosity.
  • Lacquer
    a deposit resulting from the oxidation and polymerization of fuels and lubricants when exposed to high temperatures. Similar to, but harder than, varnish.
  • Laminar particle
    wear analysis-specific term for very thin free metal flakes which are generated during the life of a rolling element bearing, but whose increased presence is generally accepted as preceding deep spalling.
  • Liquid
    any substance that flows readily or changes in response to the smallest influence. More generally, any substance in which the force required to produce a deformation depends on the rate of deformation rather than on the magnitude of the deformation.
  • Load-carrying capacity
    property of a lubricant to form a film on the lubricated surface, which resists rupture under given load conditions. Expressed as maximum load the lubricated system can support without failure or excessive wear.
  • Lubricant
    any usually oily liquid or solid of vegetable, animal, mineral or synthetic origin that reduces friction, heat and wear when applied to the surfaces of moving parts.
  • Lubricity
    ability of an oil or grease to lubricate; also called film strength.
  • Magnetic filter
    a filter element which removes additional ferromagnetic particles from the filtered fluid by the action of one or more magnets built into the filter body.
  • Magnetic plug
    solid plug with a magnetic tip protruding into a dynamically circulating part of the oil system. This plug attracts and removes ferromagnetic particles, thus providing a visual condition indicator of the presence of larger iron alloy and similar debris in the oil system. Although it does(...)
  • Maintenance
    group or sequence of gears which perform a desired mechanical transfer of power. Selected gear train types are: Scheduled maintenance Performed to reduce the possibility of or prevent the occurrence of a life-limited failure. See preventive maintenance. Unscheduled maintenance Performed(...)
  • Manifold
    an assembly containing multiple inlet and/or outlet ports and integral relating components servicing more than one area. For example, an intake manifold which delivers air to multiple cylinders, or a filter manifold which directs and collects oil from multiple filter sets.
  • Manifold filter
    a filter in which the inlet and outlet port axes are at right angles, and the filter element axis is parallel to either port axis.
  • Matrix
    the components of the sample other than the elements of interest. In spectroscopy, the matrix can cause result changes through spectral interference or viscosity change.
  • Matrix matching
    an approach to instrument operation in which the calibrations and standardizations of the instrument attempt to match the major chemical compositions of the standards, blanks, and samples in order to reduce the effect of the sample matrix on the analysis results.
  • Media
    with respect to filtration, the plural of ‘medium’.
  • Media migration
    portions of the filter medium itself passing into the effluent (downstream) from the filter.
  • Medium
    the porous material that performs the actual process of filtration.
  • Micron, micrometer (µm)
    a unit of length. One micron = 39 millionths of an inch (.000039"). Contaminant size is usually described in microns. Relatively speaking, a grain of salt is about 60 microns and the eye can see particles to about 40 microns. Many hydraulic filters are required to be efficient in capturing a(...)
  • Middle distillate
    one of the distillates obtained between kerosene and lubricating oil fractions in the refining processes. These include light fuel oils and diesel fuel.
  • MIL-Spec
    military specification; a guide in determining the quality requirements of products used by the military services, published by the United States Department of Defense.
  • Mineral oil
    any petroleum oil, as opposed to animal or vegetable-based oils.
  • Miscible
    capable of being mixed in any concentration without separation of phases; e.g., water and ethyl alcohol are miscible.
  • Motor
    a device which converts fluid power into mechanical force and motion.
  • Multigrade oil
    one of the multiviscosity number oils in which one oil combines three SAE viscosity number grades. For example, multigrade SAE 1 OW-40 grade may be used where SAE 1 OW, SAE 20W, SAE 20, SAE 30, or SAE 40 grades are specified. These oils are made possible by improved refining processes and the(...)
  • Multigrade oil
    an oil meeting the requirements of more than one SAE viscosity grade classification, and may therefore be suitable for use over a wider temperature range than a single-grade oil.
  • Multipass or recirculation test
    filter performance tests in which the contaminated fluid is allowed to recirculate through the filter for the duration of the test. Contaminant is usually added to the test fluid during the test. The test is used to determine the beta ratio (relation of pre- to post-filter fluid cleanliness).
  • Naphthenic
    a type of petroleum fluid derived from naphthenic crude oil. Characterized by low pour point (due to low wax content), and good solvency properties.
  • Napthene
    hydrocarbon characterized by saturated carbon atoms in a ring structure, having the general formula CnH2n; also called cycloparaffin or cycloalkane.
  • Neutralization number
    a measure of the total acidity or basicity of an oil; this includes organic or inorganic acids or bases or a combination thereof.
  • Newtonian fluid
    a fluid whose viscosity does not change with the rate of flow / shear. So-called multigrade oils are non-Newtonian because viscosity varies with shear rate.
  • Nitration
    specific to internal combustion engines, the formation of nitrogen oxides (NOx) during fuel combustion. NOx escapes the combustion area via ring blowby and reacts with water in the crankcase to form nitrous acid (HNO2), which can degrade the oil and increase oil viscosity. Nitration is a(...)
  • NLGI number
    one of a series of numbers classifying the consistency range of lubricating greases, based on the ASTM cone penetration number. The National Lubricating Grease Institute (NLGI) grades are in order of increasing consistency (hardness).
  • Noble metal
    a metal with marked resistance to chemical reaction, particularly to oxidation and to solution by inorganic acids. Contrast with active metal.
  • Nominal filtration rating
    filter rating indicating the approximate particle size for which the majority will not pass through a given filter. It is generally interpreted as meaning that 85% of the particles of size equal to the nominal filter rating will be retained by the filter. Due to unreproducibility and lack of(...)
  • Non-Newtonian fluid
    fluid, such as a grease or a polymer-containing oil (e.g., multi-grade oil), in which shear stress is not proportional to shear rate.
  • Octane number
    term numerically indicating the relative antiknock value of a gasoline. For octane numbers 100 or below, it is based upon a comparison with the reference fuels isooctane (100 octane number) and n-heptane (0 octane number). The octane number of an unknown fuel is the percent by volume of(...)
  • Oil analysis
    generic term for scientific examination of fluid properties, entrained wear and contamination for a variety of purposes. Selected goals and capabilities of oil analysis include: Assay Tests are performed to examine and determine a sample's characteristics, specifically related to the(...)
  • Oil drain interval
    time between complete oil drains from a sump or crankcase.
  • Oiliness
    a loose ring, the inner surface of which rides a shaft or journal and dips into a reservoir of lubricant from which it carries the lubricant to the top of a bearing by its rotation with the shaft.
  • Oxidation
    the chemical combination of a substance with oxygen. All petroleum products are subject to oxidation, with resultant degradation of their composition and performance. The organic acids formed by oxidation are corrosive to metals. The process is accelerated by heat, light, metal catalysts and(...)
  • Oxidation stability
    ability of a substance to resist natural degradation upon contact with oxygen.
  • Pale oil
    base or process oil refined until its color, by transmitted light, is straw to pale yellow.
  • Paraffinic
    a type of petroleum fluid derived from paraffinic crude oil and containing a high proportion of straight chain saturated hydrocarbons. Often susceptible to cold flow problems.
  • Particle
    a minute quantity or solid fragment, not necessarily of uniform composition. Particle size, quantity and characteristics (composition, shape, surface features, color, etc.) are all important factors considered in a total fluid analysis. A particle’s visual characteristics may be described(...)
  • Particle count
    the number of particles present greater than a particular micron size per unit volume of fluid. Selected methods of particle counting are: automated optical where particles are directly sized and counted using the dispersion or blockage of light created by a solid particle passing between a(...)
  • Patch test
    a method by which a specified volume of fluid is filtered through a membrane filter of known pore structure. All particulate matter in excess of an "average size," determined by the membrane characteristics, is retained on its surface. Thus, the membrane is discolored by an amount proportional(...)
  • Penetration
    consistency, expressed as the distance in millimeters that a standard needle or cone penetrates vertically into a sample of the material (for example, grease) under known conditions of loading, time, and temperature.
  • Permeability
    the relationship of flow per unit area to differential pressure across a filter medium.
  • pH
    measure of alkalinity or acidity in water and water-containing fluids. pH can be used to determine the corrosion-inhibiting characteristic in water-based fluids. Typically, pH > 8.0 is required to inhibit corrosion of iron and ferrous alloys in water-based fluids.
  • Pinion
    the smaller of two mating or meshing gears; may apply to either the driving or the driven gear.
  • Platelet
    wear analysis-specific term for a smooth-surfaced, irregular or round-edged flake whose appearance is "plate-like", associated with rolling element bearing fatigue; also known as spall flakes.
  • Pleated filter
    a filter element whose medium consists of a series of uniform folds and has the geometric form of a cylinder, cone, disc, plate, etc. Synonymous with "convoluted" and "corrugated".
  • Pneumatics
    engineering science pertaining to gaseous pressure and flow.
  • Poise (absolute viscosity)
    a unit of viscosity equal to the viscosity of a fluid that would require a shearing force of one dyne to move a square-centimeter area of either of two parallel layers of fluid one centimeter apart, with a velocity of one centimeter per second relative to the other layer, with the space(...)
  • Polar compound
    a chemical compound whose molecules exhibit electrically positive characteristics at one extremity and negative characteristics at the other. Polar compounds are used as additives in many petroleum products. Polarity gives certain molecules a strong affinity for solid surfaces; as lubricant(...)
  • Polishing (bore)
    excessive smoothing of the surface finish of the cylinder bore or cylinder liner in an engine to a mirror-like appearance, resulting in decreased ring seal and increased oil consumption.
  • Polymerization
    the chemical combination of similar-type molecules to form larger molecules, often in chain-like structures.
  • Pore
    small channel or opening in a filter medium which allows passage of fluid.
  • Pore size distribution
    the ratio of the number of effective holes of a given size to the total number of effective holes per unit area expressed as a percent and as a function of hole size.
  • Porosity
    the ratio of pore volume to total volume of a filter medium expressed as a percent.
  • Positive crankcase ventilation (PCV)
    system for removing blow-by gases from the crankcase and returning them through the carburetor intake manifold to the combustion chamber where the recirculated hydrocarbons are burned. A PC valve controls the flow of gases from the crankcase to reduce hydrocarbon emissions.
  • Power unit
    a combination of pump, pump drive, reservoir, controls and conditioning components which may be required for its application.
  • Pressure
    force per unit area, usually expressed in pounds per square inch.
  • Pressure, absolute
    the sum of atmospheric and gage pressures.
  • Pressure, atmospheric
    pressure exerted by the atmosphere at any specific location. (Sea level pressure is approximately 14.7 pounds per square inch absolute.)
  • Pressure, back
    the pressure encountered on the return side of a system.
  • Pressure, cracking
    the pressure at which a pressure operated valve begins to pass fluid.
  • Pressure drop
    Resistance to flow created by the element (media) in a filter. Defined as the difference between upstream pressure (filter inlet) and downstream pressure (filter outlet).
  • Pressure line filter
    filter located in a line conducting working fluid to a working device or devices.
  • Pressure, rated
    the qualified operating pressure which is recommended for a component or a system by the manufacturer.
  • Pressure, system
    the pressure which overcomes the total resistances in a system. It includes all losses as well as useful work.
  • Process contamination
    unwanted solids or liquids entering one part of a process from another part of the same process, but generally not referring to operating environment sources.
  • Process oil
    an oil not used for lubrication but as a component of another material, or as a carrier of other products.
  • Pump
    a device which applies mechanical force and motion to a liquid, creating hydraulic fluid power. Pumps are divided into two categories: Positive displacement pumps force liquid to flow in volume proportion to increasing and decreasing pump volume, as in reciprocating and rotary pumps.(...)
  • Pump, fixed displacement
    pump in which the displacement per cycle cannot be varied.
  • Pump, variable displacement
    a pump in which the displacement per cycle can be varied.
  • Pumpability
    the low temperature, low shear stress-shear rate viscosity characteristics of an oil that permit satisfactory flow to and from the engine oil pump and subsequent lubrication of moving components.
  • Rate of shear
    the difference between the velocities along the parallel faces of a fluid element divided by the distance between the faces.
  • Reducer
    a connector having a smaller line size at one end than the other.
  • Refraction
    the change of direction or speed of light as it passes from one medium to another.
  • Rerefining
    a process of reclaiming used lubricant oils and restoring them to a condition similar to that of virgin stocks by filtration, clay adsorption or more elaborate methods.
  • Reservoir
    a container for storage of liquid in a fluid power system.
  • Reservoir (sump) filter
    a filter installed in a reservoir in series with a suction or return line.
  • Residual dirt capacity
    the dirt capacity remaining in a service loaded filter element after use, but before cleaning, measured under the same conditions as the dirt capacity of a new filter element.
  • Return line
    a location in a line conducting fluid from working device to reservoir.
  • Return Line Filtration
    filters located upstream of the reservoir but after fluid has passed through the system's output components (cylinders, motors, etc.).
  • Ring lubrication
    a system of lubrication in which the lubricant is supplied to the bearing by an oil ring.
  • Ring sticking
    freezing of a piston ring in its groove in a piston engine or reciprocating compressor due to heavy deposits in the piston ring zone.
  • Rings
    circular metallic elements that ride in the grooves of a piston and provide compression sealing during combustion. Also used to spread oil for lubrication.
  • Roll-off cleanliness
    the fluid system contamination level at the time of release from an assembly or overhaul line. Fluid system life can be shortened significantly by full-load operation under a high fluid contamination condition for just a few hours. Contaminant implanted and generated during the break-in period(...)
  • Roller bearing
    an antifriction bearing comprising rolling elements in the form of rollers.
  • Rust
    a corrosion product consisting of hydrated oxides of iron.
  • Rust prevention test
    a test for determining the ability of an oil to aid in preventing the rusting of ferrous parts in the presence of water.
  • SAE viscosity numbe
    system for classifying crankcase, transmission, and differential lubricants, according to their viscosities, established by the Society of Automotive Engineers. SAE numbers are used in connection with recommendations for crankcase oils to meet various design, service, and temperature(...)
  • Saturation level
    the amount of water that can dissolve in a fluid.
  • Saybolt Universal Viscosity (SUV) or Saybolt Universal Seconds, (SUS)
    the time in seconds required for 60 cubic centimeters of a fluid to flow through the orifice of the Standard Saybolt Universal Viscometer at a given temperature under specified conditions. (ASTM Designation D 88.)
  • Scuffing
    abnormal engine wear due to localized welding and fracture. It can be prevented through the use of antiwear, extreme-pressure and friction modifier additives.
  • Semisoli
    any substance having the attributes of both a solid and a liquid. Similar to semiliquid but being more closely related to a solid than a liquid. More generally, any substance in which the force required to produce a deformation depends both on the magnitude and on the rate of the deformation.
  • Shear rate
    rate at which adjacent layers of fluid move with respect to each other, usually expressed as reciprocal seconds.
  • Shear stress
    frictional force overcome in sliding one "layer" of fluid along another, as in any fluid flow. The shear stress of a petroleum oil or other Newtonian fluid at a given temperature varies directly with shear rate (velocity). The ratio between shear stress and shear rate is constant; this ratio(...)
  • Silt
    contaminant particles 5 µm and less in size.
  • Silting
    a failure generally associated with a valve which movements are restricted due to small particles that have wedged in between critical clearances (e.g., the spool and bore.)
  • Single-pass test
    filter performance tests in which contaminant which passes through a test filter is not allowed to recirculate back to the test filter.
  • Sintered medium
    a metallic or nonmetallic filter medium processed to cause diffusion bonds at all contacting points.
  • Sleeve bearing
    a journal bearing, usually a full journal bearing.
  • Sludge
    insoluble material formed as a result either of deterioration reactions in an oil or of contamination of an oil, or both.
  • Soap
    general term denoting the salt of a fatty acid. The ordinary soaps are those of sodium and potassium. The soaps of lithium, calcium, sodium, and aluminum are the principal thickeners used in grease making.
  • Solid
    any substance having a definite shape which it does not readily relinquish. More generally, any substance in which the force required to produce a deformation depends upon the magnitude of the deformation rather than upon the rate of deformation.
  • Solvency
    ability of a fluid to dissolve inorganic materials and polymers, which is a function of aromaticity.
  • Spall
    to break up or damage a surface by moderate to deep cracking or flaking.
  • Specific gravity
    the ratio of the weight of a given volume of material to the weight of an equal volume of water.
  • Spectrometry
    using the analysis of electromagnetic radiation (light) to determine trace elements and their concentrations in a sample. In the atomic spectrometry techniques most commonly used for trace element analysis, the sample is decomposed by intense heat into a cloud of hot gases containing free(...)
  • Spin-on filter
    a throw-away type bowl and element assembly that mates with a permanently installed head.
  • Spindle oil
    a light-bodied oil used principally for lubricating textile spindles and for light, high-speed machinery.
  • Splash lubrication
    a system of lubrication in which parts of a mechanism dip into and splash the lubricant onto themselves and/or other parts of the mechanism.
  • Stainless steel
    any of several steels containing 12% to 30% chromium as the principal alloying element; the steels usually are passive in aqueous environments.
  • Starting fluid (diesel)
    a fluid, such as diethyl ether, which has a wide flammability range; used to start diesel engines at extremely low temperatures.
  • Static friction
    the force just sufficient to initiate relative motion between two bodies under load. The value of the static friction at the instant relative motion begins is termed break-away friction.
  • Statistical process control
    use of control charts and appropriate procedures to track and eliminate unacceptable physical variables in repetitive manufacturing processes.
  • Statistical quality control
    use of control charts and appropriate procedures to demonstrate consistency in the final quality of a product.
  • Stoke (St)
    standard metric kinematic unit of measurement of a fluid's resistance to flow, defined by the ratio of the fluid's dynamic viscosity to its density, equal to 1 cm2 s-1. The standard reporting unit of measurement for kinematic viscosity is the centistoke, equal to 1/100 of a stoke.
  • Strainer
    a coarse filter element (pore size over approximately 40 µm).
  • Stringer
    wear analysis-specific term for a stringlike or striplike formation of small joined flakes, usually associated with groups of small platelets which have not separated into individual particles.
  • Suction filter
    a pump intake-line filter in which the fluid is below atmospheric pressure.
  • Sulfated ash
    the ash content of fresh, compounded lubricating oil as determined by ASTM Method D 874. Indicates level of metallic additives in the oil.
  • Sulfurized oil
    oil to which sulfur or sulfur compounds have been added.
  • Surface filtration
    filtration which primarily retains contaminant on the influent surface.
  • Surface tension
    the contractile surface force of a liquid by which it tends to assume a spherical form and to present the least possible surface. It is expressed in dynes/cm or ergs/cm2.
  • Surfactant
    surface-active agent that reduces interfacial tension of a liquid. A surfactant used in a petroleum oil may increase the oil's affinity for metals and other materials.
  • Surge
    a momentary rise of pressure in a circuit.
  • Swarf
    the cuttings, and grinding fines that result from metal working operations.
  • Switch, pressure
    an electric switch operated by fluid pressure.
  • Synthetic lubricant
    a lubricant produced by chemical synthesis rather than by extraction or refinement of petroleum to produce a compound with planned and predictable properties.
  • Synthetic oil
    lubricant produced by synthesis rather than by extraction or refinement.
  • Tensile strength
    the ratio of maximum load to original cross-sectional area. Also called ultimate strength.
  • Thermal conductivity
    measure of the ability of a solid or liquid to transfer heat.
  • Thermal stability
    ability of a fuel or lubricant to resist oxidation under high temperature operating conditions.
  • Thermography
    the use of infrared thermography whereby temperatures of a wide variety of targets can be measured remotely and without contact. This is accomplished by measuring the infrared energy radiating from the surface of the target and converting this measurement to an equivalent surface temperature.
  • Thin film lubrication
    a condition of lubrication in which the film thickness of the lubricant is such that the friction between the surfaces is determined by the properties of the surfaces as well as by the viscosity of the lubricant.
  • Thixotropy
    tendency of grease or other material to soften of flow when subjected to a shearing stress, followed by a return to original consistency when the stress is removed.
  • Traceability
    the ability to trace a reported measurement through an unbroken chain of comparisons to a national or international standard.
  • Tribology
    the science and technology of interacting surfaces in relative motion, including the study of lubrication, friction and wear. Tribological wear is wear that occurs as a result of relative motion at the surface.
  • Turbidity
    the degree of opacity of a fluid.
  • Turbulent flow sampler
    a sampler that contains a flow path in which turbulence is induced in the main stream by abruptly changing the direction of the fluid.
  • Unloading
    release of stored pressure from a circuit or accumulator; release of trapped contaminant initially captured by a filter medium.
  • Vacuum separator
    a separator that utilizes subatmospheric pressure to remove certain gases and liquids from another liquid because of their difference in vapor pressure.
  • Valve
    a device which controls fluid flow direction, pressure, or flow rate.
  • Valve, by-pass
    a valve whose primary function is to provide an alternate flow path.
  • Valve, directional contro
    a valve whose primary function is to direct or prevent flow through selected passages.
  • Valve, directional control, servo
    a directional control valve which modulates flow or pressure as a function of its input signal.
  • Valve, flow contro
    valve whose primary function is to control flow rate.
  • Valve lifter
    sometimes called a "cam follower," a component in engine designs that use a linkage system between a cam and the valve it operates. The lifter typically translates the rotational motion of the cam to a reciprocating linear motion in the linkage system.
  • Valve, pressure control, relief
    a pressure control valve whose primary function is to limit system pressure.
  • Valve, relief, differential pressure
    valve whose primary function is to limit differential pressure.
  • Vapor pressure
    pressure of a confined vapor in equilibrium with its liquid at specified temperature thus, a measure of a liquid's volatility.
  • Vapor Pressure (Reid method or RVP)
    measure of the pressure of vapor accumulated above a sample of gasoline or other volatile fuel in a standard bomb at 100°F (37.8°C). Used to predict the vapor locking tendencies of the fuel in a vehicle's fuel system. Controlled by law in some areas to limit air pollution from hydrocarbon(...)
  • Varnish
    a thin film deposit resulting from the oxidation and polymerization of fuels and lubricants. Similar to but softer than lacquer, and not removable by mechanical wiping.
  • Viscometer or Viscosimeter
    an apparatus for determining the viscosity of a fluid.
  • Viscosity
    measurement of a fluid's resistance to flow. The common metric unit of absolute viscosity is the poise, which is defined as the force in dynes required to move a surface one square centimeter in area past a parallel surface at a speed of one centimeter per second, with the surfaces separated(...)
  • Viscosity, absolute
    the ration of the shearing stress to the shear rate of a fluid. It is usually expressed in centipoise.
  • Viscosity grade
    any of a number of systems which characterize lubricants according to viscosity for particular applications, such as industrial oils, gear oils, automotive engine oils, automotive gear oils, and aircraft piston engine oils. ISO and SAE are the two systems most often encountered in oil analysis(...)
  • Viscosity index (VI)
    empirical unitless number indicating the effect of temperature change on the kinematic viscosity of an oil. The higher the viscosity index, the smaller the relative change in viscosity with temperature.
  • Viscosity, kinematic
    the absolute viscosity divided by the density of the fluid. It is usually expressed in centistokes.
  • Viscosity, SUS
    Saybolt Universal Seconds (SUS), which is the time in seconds for 60 milliliters of oil to flow through a standard orifice at a given temperature. This viscosity system is still in limited use, although it has been generally replaced by the ISO grading system.
  • Viscous
    possessing viscosity. Frequently used to imply high viscosity.
  • Volatility
    expression of evaporation tendency; the degree and rate at which a liquid vaporizes under set parameters of temperature and pressure. The more volatile a petroleum liquid, the lower its boiling point and the greater its flammability. Changes in liquid stability may result in reduced volatility.
  • Wear
    the attrition or rubbing away of the surface of a material as a result of mechanical action. There is some difference of opinion on types of wear. Selected wear types are: Abrasive wearkeep sludge, carbon and other deposit precursors suspendedA cutting or scratching action caused when(...)
  • Wicking
    the active absorption of a liquid into a porous material by capillary forces.
  • Worked penetration
    the penetration of a sample of lubricating grease immediately after it has been brought to 77°F and then subjected to 60 stokes in a standard grease worker.
  • ZDDP
    common abbreviated term for an antiwear additive found in many types of hydraulic and lubricating fluids, specifically zinc dialkyldithiophosphate.