Hydraulics Glossary: H

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A glossary of the key terms you may encounter when working with hydraulic systems. Introducing the letter 'H'…

HEAD:
Vertical distance measured between two stages in a liquid. The measure of pressure at the base or other reference point of a  column of fluid. Usually measured in feet of water.
HEAT EXCHANGER:
A device which transfers heat through a conducting wall from one fluid to another. (Typically to cool a system.) Hydraulic components that help relieve the excessive heat that builds up in a hydraulic system. See also under COOLER.
The ability to resist deterioration caused by raised temperatures.
The measure of energy used when describing the normal power level in a system. The horsepower required to drive a hydraulic pump is dependent on both pressure and output in GPM. The higher the pressure, or greater the volume, the more Horsepower (HP) required. As a rule of thumb, a 1000 PSI (pounds per square inch) pump will require 1 Horsepower (HP), for the first gallon per minute and 3/4 HP each gallon per minute after that. Doubling the pressure or output volume will require 4 time the input HP. The maths: Input HP= GPM x PSI / 1714
A type of hydraulic fluid conductor that joins other hydraulic components usually in a non-linear fashion, used to transport fluid between components in a fluid power system. Hose bends and flexes and is the most versatile hydraulic conductor.
The tendency for a system to oscillate continuously.
The piece of machinery that receives pressure from the energised fluid and then converts it to motion and mechanical force.
The condition or state of equal opposed hydraulic forces acting on a part in a hydraulic component.
A control which is actuated by hydraulically induced forces.
Hydraulic control systems are controls that use fluid-based operation rather than electronics or pneumatic power.
Hydraulic control systems rely on Pascal’s Law which states that liquid pressure will remain equally distributed within a sealed system. The internal fluid moves throughout the machine’s inner workings when control units within these systems are shifted; transferring force throughout the system to shift gears or influence motion.
Many modern machines rely on either hydraulic controls or a hybrid electric-hydraulic system. Some of the main advantages to using these systems are the ability to: handle very large loads or forces, handle sudden changes in load and deliver precise and accurate handling in more specialised applications.
A machine’s operation can be influenced in a number of ways. The most basic involves manual control, where a human or robotic users activates a switch, lever or steering wheel to drive hydraulic fluid throughout the system to achieve the desired action.
Hydraulic cylinders transform the pressure and oil flow in a hydraulic system into work or mechanical force. They are used where linear motion is required to move something. Hydraulic cylinders are usually double-acting, that is, oil under pressure can be applied to either side of the piston to provide movement in either direction. Single acting hydraulic cylinders are sometimes used where the weight of the load is used to return the hydraulic cylinder to the closed position.
A liquid such as oil or water that is used to generate power in a hydraulic system.
A hydraulic component that converts low pressure from a large linear actuator into high pressure in a small linear actuator. Also called boosters, intensifiers are usually two different-sized hydraulic cylinders connected by a common piston.

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A device which converts the energy from liquid flow into mechanical motion. However, instead of a hydraulic cylinder (force moving linear) the hydraulic motor uses hydraulic pressure to rotate. In terms of how it’s built, a motor is like a pump. But, when it’s operated oil enters the hydraulic motor and turns the shaft. The speed of a hydraulic motor is dependent on the amount of oil supplied by the hydraulic pump and the torque is dependent on the amount of pressure supplied. See hydraulic motors.
Power derived from the motion and pressure of a liquid, such as water or oil. Also see under FLUID POWER.
Any device used to create kinetic energy within a hydraulic system. Motors and manual energy are both sources of power in hydraulic power units.
A device that converts mechanical force and motion into fluid power; used to move liquids in a hydraulic system.
A device used to troubleshoot and check hydraulic powered system components.
A device used to regulate fluid distribution in hydraulic applications.
The science dealing with the transmission of force through the medium of a contained fluid.
Engineering science relating to the energy of liquids in motion.
The combination of hydraulic and pneumatic fluid power.
Engineering science relating to the energy of liquids at rest. 
The use of liquid to test a hose or hose assembly for leakage, twisting and/or changes in hose length.
Combination of one or more hydraulic pumps and motors forming a unit.

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