Hydraulics Glossary: E

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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 'E'…

A wall of varying thickness.

The ratio of output to input. Volumetric efficiency of a pump is the actual output, in gallons per minute, divided by the theoretical or design output. The overall efficiency of a hydraulic system is the output power divided by the input power. Efficiency is usually expressed as a percentage.

The escape, usually of gases, through a medium.

Polymeric materials, including natural rubber or thermoplastic, that will soften when heated.

An electro-mechanical device that converts electrical power into rotary motion. The resultant power output is measured in horsepower.

A servo-valve which is capable of continuously controlling hydraulic output as a function of an electrical input.


The increase in length expressed as a percentage of the original length.

An additive that promotes the formation of a stable mixture, or emulsion, of oil and water.

Intimate mixture of oil and water, generally of a milky or cloudy appearance.

Lubricant additive that prevents sliding metal surfaces from seizing under conditions of extreme pressure (EP).

Degradation of a surface resulting from a mixture of fluid and air or fluid and dirt particles passing over the surface at the same time as a change in pressure occurs.

A passage or channel that is open to the atmosphere. Normally used in systems using pressurised air or gases which may then be dispensed into the atmosphere.

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