The amount of contaminants a filter will hold before an excessive pressure drop is caused. Most filters have bypass valves, which open when a filter reaches its rated capacity.


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 small bore (capillary) tube.


A non-metallic element - No. 6 in the periodic table. Diamonds and graphite are pure forms of carbon. Carbon is a constituent of all organic compounds. It also occurs in combined form in many inorganic substances; i.e., carbon dioxide, limestone, etc.

Carbon residue

Coked material remaining after 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.


A substance, which speeds a chemical action without undergoing a chemical change itself during the process. Now used in catalytic converters to control amount of unburned hydrocarbons and CO in automobile exhaust.

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 machine resulting in considerable cost and downtime.


Formation of an air or vapor pocket (or bubble) due to lowering of pressure in a liquid, often as a result of a solid body, such as a propeller or piston, moving through the liquid; also, the pitting or wearing away of
a solid surface as a result of the collapse of a vapor bubble. Cavitation can occur in a hydraulic system as a result of low fluid levels that draw air into the system, producing tiny bubbles that expand explosively at the pump outlet, causing metal erosion and eventual pump destruction.

Cavitation erosion

A material-damaging process, which occurs as a result of vaporous cavitation. "Cavitation" refers to the occurrence or formation of gas- or vapor- filled pockets in flowing liquids due to the hydrodynamic generation of low pressure (below atmospheric pressure). This damage results from the hammering action when cavitation bubbles implode in the flow stream. Ultra-high pressures caused by the collapse of the vapor bubbles produce deformation, material failure and, finally, erosion of the surfaces.

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 unit of absolute viscosity. 1 centipoise = 0.01 poise.

Centistokes (cst)

A 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 have a machine or group of machines is 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.

Chemical stability

The tendency of a substance or mixture to resist chemical change.

Circulating lubrication

A system of lubrication in which the lubricant, after having passed through a bearing or group of
bearings, is re-circulated by means of a pump.


100 particles >10 micron per milliliter


A filter element which, when loaded, can be restored by a suitable process, to an acceptable percentage of its original dirt capacity.

Clearance bearing

A journal bearing in which the radius of the bearing surface is greater than the radius of the journal surface.

Cloud point

A journal bearing in which the radius of the bearing surface is greater than the radius of the journal surface.

Coefficient of friction

The number obtained by dividing the friction force resisting motion between two bodies by the normal force pressing the bodies together.


That property of a substance that causes it to resist being pulled apart by mechanical means.

Cold cranking simulator (CCS)

An intermediate shear rate viscometer that predicts the ability of oil to permit a satisfactory cranking speed to be developed in a cold engine.


An inward structural failure of a filter element, which can occur due to abnormally high-pressure drop (differential pressure) or resistance to flow.

Collapse pressure

The minimum differential pressure that an element is designed to withstand without permanent deformation.


(1) Chemically speaking, 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. (2) In petroleum processing, generally connotes fatty oils and similar materials foreign to petroleum added to lubricants to impart special properties.

Compounded oil

Petroleum oil to which has been added other chemical substances.


A compound that enhances some property of, or imparts some new property to, the base fluid. In some hydraulic fluid formulations, the additive volume may constitute as much as 20 percent of the final composition. The more important types of additives include anti-oxidants, anti-wear additives, corrosion inhibitors, viscosity index improvers, and foam suppressants.

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.


A device, which converts mechanical force and motion into pneumatic fluid power.


The degree to which a semisolid material such as grease resists deformation. (See ASTM designation D 217.) Sometimes used qualitatively to denote viscosity of liquids.


Any foreign or unwanted substance that can have a negative effect on system operation, life or reliability.

Contaminant (Dirt, ACFTD) capacity

The weight of a specified artificial contaminant that must be added to the influent to produce a given differential pressure across a filter at specified conditions. Used as an indication of relative service life.

Contamination control

A broad subject, which 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.


A fluid used to remove heat. See Cutting fluid.

Copper strip corrosion

A qualitative measure of the tendency of a petroleum product to corrode pure copper.


The internal duct and filter media support.


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.

Corrosion inhibitor

Additive for protecting lubricated metal surfaces against chemical attack by water or other contaminants. There are several types of corrosion inhibitors. Polar compounds wet the metal surface preferentially, protecting it with a film of oil. Other compounds may absorb water by incorporating it in a water-in-oil emulsion so that only the oil touches the metal surface. Another type of corrosion inhibitor combines chemically with the metal to present a non-reactive surface.

Coupling, quick disconnect

Couplings, which can quickly joins or separate lines.


The processes whereby large molecules are broken down by the application of heat and pressure to form smaller molecules.


The top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.

Cutting fluid

Any fluid applied to a cutting tool to assist in the cutting operation by cooling, lubricating or other means.


A single complete operation consisting of progressive phases starting and ending at the neutral position.


A device, which 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