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:

	TERM DESCRIPTION Occurrence Any detected or diagnosed fault requiring remedial action whether the action was reactive, preventive or proactive Apparent Fault Condition A diagnostic system reading indicates an abnormal condition, pending confirmation and evaluation of severity True Fault Condition An apparent fault condition has been confirmed as a valid abnormal condition (by inspection, multi-technique cross checking, loss or variance in performance, etc.) False Alarm An apparent fault condition has not been confirmed or has been traced to an external cause (sampling or instrument error, misidentification, judgement error, etc.)

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 of wear, and possible source.

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 to reach terminal conditions at a specified contaminant addition rate.

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 burn at the ignition source but will not propagate a flame back through a spray mist to the leak. They will self-extinguish when the ignition source is removed. Three common types of fire-resistant fluids are:

water-petroleum oil emulsions, in which the water prevents burning of the petroleum constituent;

water-glycol fluids, which are essentially non-flammable by nature;

non-aqueous fluids of low volatility, such as phosphate esters, silicones, and halogenated hydrocarbons.

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, laminar -- fluid flow in parallel layers.

Flow, turbulent – fluid flow in random directions.

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 rate -- the volume, mass, or weight of a fluid passing through any conductor per unit of time.

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.

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.

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 and compression of all types of frequency-based information. In oil analysis, the "FT" portion of "FTIR".

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.