Filter - 1. A device whose primary function is the removal by porous media of insoluble contaminants from a liquid or a gas. 2. Chemically inert, finely divided material added to the elastomer to aid in processing and improve physical properties.

Filter, strainer - A coarse hydraulic filter usually of woven wire construction. This may be in the form of a complete filter or just an element.

Filter, by-pass (reserve) A filter which provides an alternate unfiltered flow path around the filter element when a preset differential pressure is reached.

Filter, spin-on - A filter with spin-on element sealed in its own pressure housing for independent mounting to the filter.

Filtration ratio (βm) - The ratio of the number of particles greater than a given size (β) in the influent fluid to the number of particles greater than the same size (m) in the effluent fluid.

Fitting - A connector or closure for fluid power lines and passages.

Fitting, compression - A fitting which seals and grips by manual adjustable deformation.

Fitting, flange - A fitting which utilizes a radially extending collar for sealing and connection.

Fitting, flared - A fitting which seals and grips by a pre-formed flare at the end of the tube.

Fitting, flareless - A fitting which seals and grips by means other than a flare.

Flash point - The temperature to which a liquid must be heated under specified conditions of the test method to give off sufficient vapor to form a mixture with air that can be ignited momentarily by a flame.

Flip flop - A digital component or circuit with two stable states and sufficient hysteresis so that it has "memory." Its state is changed with a control pulse; a continuous control signal is not necessary for it to remain in a given state.

Flow characteristic curve - The change in regulated (secondary) pressure occurring as a result of a change in the rate of air flow over the operating range of the regulator.

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

Flow, laminar (streamline) - A flow situation in which fluid moves in parallel lamina or layers.

Flow, output - Flow rate discharged at the outlet port.

Flow, turbulent - A flow situation in which the fluid particles move in a random fluctuating manner.

Flow - Movement of fluid generated by pressure differences.

Fluid capacity - The liquid volume coincident with the "high" mark of the level indicator.

Fluid friction - Friction due to the viscosity of fluids.

Fluid logic - A branch of fluid power associated with digital signal sensing and information processing, using components with or without moving parts.

Fluid miscibility - Capacity of fluids to be mixed in any ratio without separation into phases.

Fluid power system - A system that transmits and controls power through use of a pressurized fluid within an enclosed circuit.

Fluid power - Energy transmitted and controlled through use of a pressurized fluid.

Fluid stability - Resistance of a fluid to permanent changes in properties.

Fluid stability, oxidation - Resistance of a fluid to permanent changes caused by chemical reaction with oxygen.

Fluid, anti-corrosive - A fluid containing metal corrosion inhibitors.

Fluid, aqueous - A fluid which contains water as a major constituent besides the organic material. The fire resistance properties are derived from the water content.

Fluid, fire resistant - A fluid difficult to ignite which shows little tendency to propagate flame.

Fluid, hydraulic - A fluid suitable for use in a hydraulic system.

Fluid, Newtonian - Fluid having a viscosity that is always independent of the rate of shear.

Fluid, pneumatic - A fluid suitable for use in a pneumatic system, usually air.

Fluid, rust protection - Capacity of a fluid to prevent the formation of rust under specified conditions.

Fluid - A liquid, gas or combination thereof.

Force motor - A type of electromechanical transducer having linear motion used in the input stages of servovalves.

Free air - Any compressible gas, air or vapor trapped within a hydraulic system that does not condense or dissolve to form a part of the system fluid.

Free water - Water droplets or globules in the system fluid that tend to accumulate at the bottom or top of the system fluid depending on the fluid's specific gravity.

Frequency response - The changes, under steady-state conditions, in the output variable which are caused by a sinusoidal input variable.