CHAPTER 5 – GLOSSARY of HYDRAULIC TERMS
| Accumulator: | A device for storing hydraulic energy. |
| Actuator: | A device that converts hydraulic energy into mechanical energy. (e.g., cylinders, motors.) |
| Aeration: | Air in the fluid. |
| Cant: | The leaning or tilt of an object, especially sideways. |
| Cavitation: | Air bubbles or pockets created in hydraulic lines and components by the turbulent flow of hydraulic fluid. |
| Cylinder: | An actuator that converts hydraulic energy into linear or rotary mechanical energy. (NOTE: Rotary cylinders usually rotate less than one full revolution.) |
| Displacement: | The volume of fluid that is transferred from the pump inlet to the outlet during one revolution of the pump. Displacement is expressed in cubic inches per revolution. |
| Energy: | The capacity for doing work. |
| Filter: | A device that removes contaminants from the hydraulic fluid and is rated in microns. |
| Flash Point: | The lowest temperature at which vapors from a volatile liquid will ignite. |
| Force: | A push or pull that is exerted on an object in order to change its position or direction of movement. |
| Fluidity: | Fluidity is the ability of the fluid to take the shape of the container it is in. |
| Horsepower: | 1 Horsepower = 33,000 foot-pounds/one minute or 1 Horsepower = 550 foot-pounds/one second |
| Hydraulics: | The study of fluids in motion or at rest. |
| Hydrodynamics: | Devices or systems that use the impact or kinetic energy in the liquid to transmit power. |
| Hydrostatics: | Devices or systems that use force applied to a confined fluid. Pressure is distributed over the area exposed to the fluid and is expressed in force per unit area (PSI). |
Incompressible Fluid: |
A fluid which is not reduced in volume by an increase in pressure. |
Laminar Flow (Streamline): |
The smooth and efficient flow of hydraulic fluid through hydraulic lines and components. |
| Line: | A tube, pipe or hose for conducting a fluid. |
| Liquid: | A fluid that is relatively incompressible. (NOTE: A gas is a fluid which is very compressible). |
| Mass: | Represents the amount of matter in an object, and its inertia or resistance to movement. |
| Micron: | A measure of size equal to one millionth of a meter, or approximately 0.000039 inch. Micron size is often used to describe the size of particles that a filter will remove from the fluid. For example, a 20 micron absolute filter is said to remove all particles greater than 20 microns. |
| Motor: | An actuator that converts hydraulic energy into rotary mechanical energy. |
| Non-positive displacement pump: | A pump in which the inlet and outlet are hydraulically connected, so that the fluid can re-circulate in the pump when pressure builds. |
| Pascals law: | Pressure in an enclosed container is transmitted equally and undiminished to all parts of the container and acts at right angles to the enclosing walls. |
| Positive displacement pump: | A pump that has the inlet sealed from the outlet. |
| Power: | An amount of work (foot-pounds) done in a given amount of time (seconds or minutes). |
| Pressure: | The force exerted over a surface divided by its area. |
| Pump: | A device that creates the flow of hydraulic fluid. (NOTE: A pump converts mechanical energy into hydraulic energy.) |
| Radial piston pump: | Where the pistons are set perpendicular to the pump’s center, like sun rays. |
| Reciprocating motion: | The movement of hydraulic fluid back and forth in cylinder bores through the use of pistons. |
| Reservoir: | A container for keeping a supply of working fluid in a hydraulic system. |
| Specific gravity: | The density or mass of a liquid. The specific gravity (SG) of a liquid is also its weight as compared to the weight of water in the same amount and at the same temperature. |
| Thermal expansion: | The dimensional changes in increased volume exhibited by solids, liquids, and gases for changes in temperature while pressure is held constant. |
| Valve: | A device that controls either pressure of fluid, direction of fluid flow, or rate of flow. |
| Viscosity: | A measure of the fluid’s resistance to flow. |
| Weight: | A result of the gravitational force or pull on the object. |
| Work: | Takes place when a force (in pounds) is moved through a distance (in feet). |