Fluid power glossary
What is in this article?:
- Fluid power glossary
- Cavitation — Cylinder, Tie Rod
- Darcy’s Formula — Expectancy, Life
- Filter — Frequency Response
- Gauge Damper —Hydrostatics
- Indicator, Differential Pressure — Ozone Resistance
- Pump — Rotation
- Seal, Cup — Synthetic Fluid
- Temperature, Ambient — Vulcanization
Absorption — Bulk Modulus
Absorption – The physical mechanism by which one substance attracts and takes up another substance (liquid, gas, or vapor) into its interior.
Accumulator – A container in which fluid is stored under pressure as a source of fluid power.
Accumulator, hydropneumatic bladder – A hydropneumatic accumulator in which the liquid and gas are separated by an elastic bag or bladder.
Actuator, pneumatic/hydraulic – A device in which power is transferred from one pressurized medium (pneumatic) to another (hydraulic) without intensification.
Additive – A chemical added to a fluid to impart new properties or enhance those that already exist.
Adsorption – The physical mechanism by which one substance attracts another substance (either solid, liquid, gas, or vapor) to its surface and causes the second substance to adhere to its surface.
Aftercooler – A device which cools a gas after it has been compressed.
Afterfilter – A filter which follows the compressed air dryer and usually for the protection of downstream equipment from desiccant dust.
Air – A gas mixture consisting of nitrogen, oxygen, argon, carbon dioxide, hydrogen, small quantities of neon, helium and other gases.
Air bleeder – A device for removal of air.
Air breather – A device permitting air movement between atmosphere and the component in which it is installed.
Air motor – A device which converts pneumatic fluid power into mechanical torque and motion. It usually provides rotary mechanical motion.
Air, compressed (pressurized) – Air at any pressure greater than atmospheric pressure.
Air, dried – Air with moisture content lower than the maximum allowable for a given application.
Air, free – Air at ambient temperature, pressure, relative humidity, and density.
Air, saturated – Air at 100% relative humidity, with a dew point equal to temperature.
Air, standard – Air at a temperature of 68.8° F, a pressure of 14.70 pounds per square inch absolute, and a relative humidity of 36% (0.0750 pounds per cubic foot). In gas industries the temperature of “standard air” is usually given as 60.8° F.
Amplification, power – The ratio between the output signal variations and the corresponding input (control) power variation (for analog devices only).
Amplification, pressure – Ratio between outlet pressure and inlet (control) pressure.
Amplification – The ratio between the output signal variations and the control signal variations (for analog devices only).
Analog – Of or pertaining to the general class of fluidic devices or circuits whose output varies as a continuous function of its input.
AND device – A control device which has its output in the logical 1 state if and only if all the control signals assume the logical 1 state.
Aniline point – The lowest temperature at which a liquid is completely miscible with an equal volume of freshly distilled aniline (ASTM Designation D611-07).
Aniline point – The lowest temperature at which equals volumes of pure, fresh aniline and an oil will completely dissolve in one another is the aniline point of the oil.
Bernoulli’s Law – If no work is done on or by a flowing frictionless liquid, its energy due to pressure and velocity remains constant at all points along the streamline.
Bleeding – Migration to the surface of plasticizers, waxes, or similar materials to form a film or beads.
Boyle’s Law – The absolute pressure of a fixed mass of gas varies inversely as the volume, provided the temperature remains constant.
Breakout Force – That force necessary to initiate sliding by overcoming static coefficient of friction. An excessive breakout force indicates the development of adhesion.
Breathing capacity – A measure of flow rate through an air breather.
Bulk modulus – The measure of a fluid’s resistance to compressibility. It is the reciprocal of compressibility.
Cavitation — Cylinder, Tie Rod
Cavitation – A localized gaseous condition within a liquid stream which occurs where the pressure is reduced to the liquid’s vapor pressure, often as a result of a solid body, such as a rapidly moving piston moving through the liquid. Also, the pitting or wearing away of a solid surface 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.
Charles’ Law – The volume of a fixed mass of gas varies directly with absolute temperature, provided the pressure remains constant.
Circuit – An arrangement of interconnected components and parts.
Cold Flexibility – Flexibility following exposure to a predetermined time.
Cold Flow – Continued deformation under stress.
Compatibility, Seal – Ability of an elastomer to resist the action of a fluid on its dimensional and mechanical properties.
Compressibility – The change in volume of a unit volume of a fluid when subjected to a unit change in pressure.
Compression Modulus – The ratio of the compressive stress to the resulting compressive strain (the latter expressed as a fraction of the original height or thickness in the direction of the force). Compression modulus may be either static or dynamic.
Compression Set – The amount by which a rubber specimen fails to return to original shape after release of the compressive load.
Compressor – A device which converts mechanical force and motion into pneumatic fluid power.
Condensation – The process of changing a vapor into a liquid condensate by the extraction of heat.
F-R-L Unit – An assembly comprising an air filter, pressure regulator, and a lubricator.
Conductor – A component whose primary function is to contain and direct fluid.
Contaminant – Any material or substance which is unwanted or adversely affects the fluid power system or components, or both.
Control – A device used to regulate the function of a component or system.
Controller – A device which senses a change of fluid state and automatically makes adjustments to maintain the state of the fluid between predetermined limits, e.g., pressures, temperatures, etc.
Copolymer – A polymer consisting of two different monomers chemically combined.
Creep – The progressive relaxation of a given rubber material while it is under stress. This relaxation eventually results in permanent deformation or “set.”
Cushion – A device which provides controlled resistance to motion.
Cylinder – A device which converts fluid power into linear mechanical force and motion. It usually consists of a movable elements such as a piston and piston rod, plunger or ram, operating within a cylindrical bore.
Cylinder cap – A cylinder end closure which completely covers the bore area.
Cylinder capacity, extending – Volume required for one full extension of a cylinder.
Cylinder capacity, retracting – Volume (annular) absorbed by one full retraction of the cylinder.
Cylinder capacity – The volume of a theoretically incompressible fluid that would be displaced by the piston during a complete stroke. (For double acting cylinders it must be given for both directions of stroke.)
Cylinder force, theoretical – The pressure multiplied by the effective piston area, ignoring friction. For double acting cylinders, the value must be given for both directions of stroke.
Cylinder, adjustable stroke – A cylinder equipped with adjustable stops at one or both ends to limit piston travel.
Cylinder area, piston rod – Cross-sectional area of the piston rod.
Cylinder area, piston, effective – Area upon which fluid pressure acts to provide a mechanical force.
Cylinder bore – The internal diameter of the cylinder body.
Cylinder, cushioned – A cylinder with a piston-assembly deceleration device at one or both ends of the stroke.
Cylinder, differential – A double acting cylinder in which the ratio of the area of the bore to the annular area between the bore and the piston rod is significant in circuit function.
Cylinder, double acting – A cylinder in which fluid force can be applied to the moveable element in either direction.
Cylinder, double rod – A cylinder with a single piston and a piston rod extending from each end.
Cylinder, dual stroke – A cylinder combination which provides two working strokes.
Cylinder, duplex – A unit comprised of two cylinders with independent control, mechanically connected on a common axis to provide three or four positions depending on the method of application.
Cylinder, piston type – A cylinder in which the piston has a greater cross-sectional area than the piston rod.
Cylinder, plunger (ram) – A cylinder in which the piston has the same cross-sectional area as the piston rod.
Cylinder, rotary actuator – A cylinder which translates piston reciprocation into oscillation of an output shaft.
Cylinder, rotating – A cylinder in which the piston and piston rod, plunger or ram, is permitted to rotate with reference to the cylinder housing.
Cylinder, single acting – A cylinder in which the fluid force can be applied to the movable element in only one direction.
Cylinder, tandem – Arrangement of at least two pistons on the same rod moving in separate
chambers on the same cylinder body allowing the compounding of force on the piston rod.
Cylinder, telescoping – Cylinder with two or more stages or extensions, achieved by hollow piston rods sliding one within the other (may be single or double acting).
Cylinder, tie rod – A cylinder with head and cap end closures that are secured by tie rods.
Darcy’s Formula — Expectancy, Life
Darcy’s Formula – A formula used to determine the pressure drop due to flow friction through a conduit.
Deliquescent – Moisture is separated by using the absorptive properties of special hygroscopic compounds.
Desiccant – Material that tends to remove moisture from compressed air.
Dew point – The temperature at which vapors in a gas condense. For practical purposes, it must be referred to a stated pressure.
Digital – Of or pertaining to the general class of fluidic devices or circuits whose output varies in discrete steps (i.e., pulses or “on-off” characteristics).
Displacement, volumetric – Volume absorbed or displaced per stroke of a cylinder or per cycle of a pump or motor.
Dissolved air – Air which is dispersed at a molecular level in hydraulic fluid to form a single phase.
Dissolved water – Water which is dispersed at a molecular level in hydraulic fluid to form a single phase.
Dither – A low amplitude, relatively high frequency periodic electrical signal, sometimes superimposed on the servovalve input to improve system resolution. Dither is expressed by the dither frequency (Hz) and the peak-to-peak dither current amplitude.
Droop – The deviation between no flow secondary pressure and secondary pressure at a given flow.
Dryer, compressed air – A device for reducing the moisture content of the working compressed air.
Durometer – 1. An instrument for measuring the hardness of rubber. Measures the resistance to the penetration of an indentor point into the surface of rubber. 2. Numerical scale of rubber hardness.
Efficiency – Ratio of output to the corresponding input.
Elasticity – The property of a material which tends to return to its original shape after deformation.
Elastomer – Any synthetic or natural material with resilience or memory sufficient to return to its original shape after distortion.
Elongation – Generally means “ultimate elongation” or percent increase in original length of a specimen when it breaks.
Emulsion, oil in water – A dispersion of oil in a continuous phase of water.
Emulsion, water in oil – A dispersion of water in a continuous phase of oil.
Emulsifier – additive that promotes formation of a stable mixture, or emulsion, of oil and water.
Emulsion – A homogeneous dispersion of two immiscible liquids, generally of a milky or cloudy appearance.
Entrained air – A mechanical mixture of air bubbles having a tendency to separate from the liquid phase.
Expectancy, life – The predicted working period during which a component or system will maintain a specified level of performance under specified conditions. Sometimes expressed in statistical terms as a probability.
Filter — Frequency Response
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.