The ABC’s of Fluid Power

The ABC’s of Fluid Power

Like many areas, the fluid power world has a very specific professional vocabulary. Here are some of the most common terms frequently used. To get your own copy of the whole fluid power glossary, contact IBT Fluid Power .

Actuator: Device in which power is transferred from one pressurized medium to another without intensification.

Air Motor: Device which converts pneumatic fluid power into mechanical torque and motion.

Bernoulli’s Law: If a flowing, frictionless fluid does no work – or is not affected by the surroundings, energy of a fluid due to pressure and velocity remains constant along all points of its streamline.

Boyle’s Law: The absolute pressure of a fixed mass of gas varies inversely as the volume, provided that temperature remains constant.

Charles’ Law: The volume of a fixed mass of gas varies directly with the absolute temperature, provided the temperature remains constant.

Compressibility: The change in volume of a unit volume of fluid when subjected to a unit change in pressure.

Compressor: Device that converts mechanical force and motion into pneumatic fluid power.

Cylinder: A device which converts fluid power into linear mechanical force and motion. It usually has a movable piton and piston rod, plunger or ram, operating within a cylindrical bore.

Durometer: Instrument that measures the hardness of rubber by measuring the resistance to penetration of an indentor point into the surface. Also the value of that measurement.

Flash Point: The temperature to which a liquid, when heated, will give off sufficient vapor that can be ignited by a flame.

Flow: Movement of fluid caused by pressure differences.

Fluid: A liquid, gas or combination of the two.

Heat exchanger: A device usually used to cool a system that transfers heat through a conducting wall from one fluid to another.

Hose: A flexible line or conductor. Nominal size is the I.D.

Hydraulic amplifier: A fluid device which has one or more inputs controlling a source of fluid power that enables the output to be multiplied. May use sliding spools, nozzle flappers, jet pipes,etc.,

Hydraulic motor: Device to convert hydraulic fluid power into mechanical force and motion.

Manifold: A conductor that has multiple connection ports.

Newt: A unit of kinematic viscosity in the English system. It is expressed in square inches per second. (see Stokes)

Pascal’s Law: A pressure applied to a confined fluid at rest is transmitted with equal intensity throughout the fluid.

Power unit: A combination of pump, pump drive, reservoir, controls and conditioning components to supply hydraulic power to a system.

Pressure: Force per unit area, usually expressed in pounds per square inch (psi) or bar.

Rated pressure: The qualified operating pressure which is recommended by the manufacturer for a component or system.

Hydraulic: Device which converts mechanical torque and motion into hydraulic fluid power.
Vane: Hydraulic pump with multiple radial vanes within a rotor.
Variable displacement: hydraulic pump in which the volume displaced per cycle can be varied

Pump motor: Unit which functions either as a pump or as a rotary motor.

Quick disconnect coupling: Component which can quickly join or separate a fluid line without the use of special tools or devices.

Rotation: The direction of rotation is always quoted as viewed looking at the shaft end. When in doubt, draw it out.

Servovalve: A valve which modulates output as a function of an input command.

Specific gravity: The ratio of the weight of a specific volume of fluid to the weight of an equal volume of water.

Stage A hydraulic amplified used in a servovalve. Servovalves may be single stage, two stage or more.

Stokes: Standard unit kinematic viscosity in the centimeter grams second system. It is expressed in square centimeters per second.

Torque motor: Type of electromechanical transducer having rotary motion used in the input stages of servovalves.

Torricelli’s Theorem: The liquid velocity at an outlet discharging into the free atmosphere is proportional to the square root of the head.

Tube: A conductor whose size is its OD. Tube is available in varied wall thickness and material.

Valve: A device which controls fluid flow, direction or flow rate.

Valve actuator: The valve part(s) through which force is applied to move or posiiton flow-directing elements.


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