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 nationally or internationally traceable standards of verified known value. Once this measurement has been performed, any deviation from required performance specifications may be corrected by adjustment, repair or replacement. Standardization connotes a procedure for making limited routine measurements and adjustments to the process or system in order to correct minor known variations, such as those associated with changes in operating environment or working materials. Calibrations are normally performed at longer intervals (annual or semi-annual) set by instrument manufacturers, official standardizing agencies, or operating circumstances, while standardizations are typically done on a daily or weekly basis. Not all simple systems or processes are readily adjustable--for example, the contents of a liquid-in-glass thermometer. In such a case the calibration would only involve determining the thermometer’s ‘true’ reading as opposed to its stated reading and applying a correction factor, without the corresponding physical adjustments normally associated with the calibration process. For complex instrument systems used in modern oil analysis laboratories, both manual and electronic calibrations and standardizations are essential in maintaining acceptable performance.

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, limestone, etc.

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 "poisoned" by lead compounds in the fuel or lubricant.

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 occur in a hydraulic system as a result of low fluid levels that draw air into the system, producing tiny bubbles that undergo explosive decompression at the pump outlet.

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.

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.

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.

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.

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 used in high-speed, close-tolerance systems such as aviation turbine engines where any release of larger iron alloy flakes or fragments is considered a serious condition.

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 content may be monitored by various types of detectors. If the method is used for separation, the column core can then be pushed out and the zones of material cut apart, or the zones can be eluted by passing more solvent down the column and collecting it in small fractions.

Gas chromatography is an analytical technique for separating mixtures of volatile substances. The procedure consists of introducing the mixture to be examined into the chromatographic column and washing it down (eluting it) with an inert gas. The column is packed with adsorbent materials that selectively retard the components of the sample. A detector profiles the sample's components, using the time each component took to reach the detector and the intensity of the detector's response to each component.

Paper chromatography is a micromethod. A drop of the liquid to be investigated is placed near one end of a strip of paper. This end is immersed in solvent that travels down the paper and distributes the materials present in the original drop selectively. Comparison with known substances makes identfication possible. The commonly used and extremely simple "blotter test" is a long-established example of the principle of paper chromatography, although it omits the solvent and standard comparison steps.

Partition chromatography involves the selective solution of the desired material between two solvents. The final solvent, usually water, is used to wet the solid material packed in the column, and the first solvent containing the desired material is poured into the column as described.

Circulating lubrication – lubricating system that recirculates fluid through a system after it has passed through the system and returned to a central collection point.

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.

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.

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.

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.

Compressibility -- the change in volume of a unit volume of a fluid when subjected to a unit change of pressure.

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.

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 would imply mixing or degradation. Another example would be the amount of dirt contamination within a system correlated to the amount of abrasive wear on the internal parts.

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.