Hydraulics Glossary: A

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Hydraulic Engineering Glossary of Terms and Terminology

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A glossary of the key hydraulic engineering terms and related terminology you may encounter when working with hydraulic systems. Introducing the letter 'A'…

ABRASION:
External damage (to the hose assembly) caused by rubbing on a foreign object, wearing away by friction.
ABSOLUTE:
A measure that at its zero or base point, has a complete absence of the entity being measured.
ABSOLUTE PRESSURE:
The indicated value of the weight of the earth’s atmosphere. At sea level this value is approximately 14.65 pounds per square inch (psi). Absolute pressure is zero-referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure.


The ratio of shear stress to shear rate. It is a hydraulic fluid’s internal resistance to flow.

The integration of one material into another.
A container or vessel, normally cylindrical, which stores hydraulic fluid or gas under pressure for future release. Used as an energy source or to absorb hydraulic shock. Designed to increase or relieve pressure in the hydraulic system. Common types of hydraulic accumulator are: piston, bladder and diaphragm. Click here to browse popular hydraulic accumulators.
The ability of the system to achieve the desired output.
A device in which power is transferred from one pressurized medium to another without intensification; the hydraulic components such as hydraulic cylinders, hydraulic motors and hydraulic rotary actuators that directly help convert hydraulic energy into mechanical energy.
A device used to align the shaft of a rotary device (e.g. and electric motor) with the shaft of a hydraulic pump to maintain radial and parallel shaft alignment. Fittings can vary in size and material to change an end fitting from one type or size to another.
A chemical added to a hydraulic fluid to impart new properties or to enhance those which already exist.

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Air trapped in the hydraulic fluid. Excessive aeration causes the hydraulic fluid to appear milky and can lead to erratic systems performance. See our article on air contamination in hydraulic systems.
A device (either manual or automatic) for the removal of air trapped in the pipeline.
A device permitting air movement between the atmosphere and the hydraulic component in which it is installed, containing a fine mesh filter element to prevent contaminants from entering the hydraulic component. Normally attached to the top of a reservoir or tank to allow air to pass in and out.
Air at any pressure greater than atmospheric pressure.
The ambient atmosphere forced or trapped into the hydraulic system during connection of quick-release coupling halves.
A hydraulic component in a hydraulic system that relieves excessive heat with cool air.
A hydraulic component used to store hydraulic fluid. The air-operated accumulator increases and relieves hydraulic pressure through the use of an inflatable bag. Also called a gas-loaded accumulator.
A hydraulic component that is powered by compressed air. Compressed air exerts force on a piston, which magnifies pressure as the hydraulic fluid escapes to smaller conductors and actuators.
Of or relating to the immediate surroundings. The current condition of temperature, humidity and atmospheric pressure.
The noise level in the surrounding area while the machine or component concerned is not operating. Background noise.

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An electronic device used to increase the strength of the signal or input voltage fed into it to modify the signal into a driving voltage or current at a different level.
The magnitude or volume of sound.
An electronic device that requires or produces an infinitely variable signal (voltage or current) in response to a state change within the device.
An AC or DC voltage or current signal that represents continuously variable physical quantities (e.g., voltage, current, pressure, temperature, or speed). Any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e. analogous to another time varying signal.
One of two types of additives used to reduce foaming in petroleum products.
A ring shaped area, often referring to the net effective area of the rod slide of a cylinder piston, i.e. the piston area of the rod.
An electrolytic process used to increase the thickness of the natural oxide layer on the surface of metal parts; to deposit protective or cosmetic coatings in a variety of colours on metal. Primarily used on aluminium.
Microscopic projections on metal surfaces resulting from normal surface-finishing processes.
The weight of the atmosphere. Atmospheric pressure refers to the amount of pressure exerted by the air at any specific location. Sea level pressure is approximately 14.7 pounds per square inch (psi) which equates to 1.01 bar.
The gradual loss in intensity of any kind of flux (current) through a medium.
A variable resistive device used to reduce current or voltage.

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