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Glossary of Terms - All Terms

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Glossary Subsets

Radial Bearing

A rolling element bearing designed primarily to support a load perpendicular to the shaft axis. Also referred to as an annular bearing.

Radial Clearance

• The average outer ring race diameter, minus the average inner ring race diameter, minus twice the ball diameter.
• Radial clearance is expressed by C0 (Normal Clearance), C1, C2, C3, C4 and C5. C2 clearance is less than normal (C0), and

Rating Life

The rating life of a group of identical bearings is the life in millions of revolutions that 90% of the group will complete or exceed. Often referred to as L10 life.


• A single acting cylinder with a plunger rather than a piston and rod.
• The plunger in a ram type cylinder.


Class or degree of precision of anti-friction roller bearings. Similar to ABEC.


Back and forth straight line motion or oscillation.


A device that converts AC power to DC power.


Regenerative drives refer to the regeneration of energy from the motor and drive back to the power source. A motor generates when the load forces the motor to go faster than the drive has set. A drive is regenerative when it puts the generated energy ba

Relieved End Roller

A roller with a slight modification of diameter at ends of the outside surface to reduce stress concentration at contacts between rollers and raceways.

Relief Valve

A pressure operated valve which bypasses pump delivery to the reservoir, limiting system pressure to a predetermined maximum value.


To add fluid to maintain a full hydraulic system.


An electric device that is designed to read input conditions in a prescribed manner.


A container for storage of liquid in a fluid power system.


The non-reactive opposition which a device or material offers to the flow of direct or alternating current. Usually measured in ohms.


An organic material that has an indefinite and often high molecular weight. Resins tend to flow when subjected to stress, usually have a softening or melting range.


One or more units possessing the property of electrical resistance. Resistors are used in electric circuits for the purpose of operation, protection, or control.


A reduced cross-sectional area in a line or passage which produces a pressure drop.

Return Line

A line used to carry exhaust fluid from the actuator back to the tank.


A device which separates the balls or rollers in a bearing. Also referred to as a cage or separator.

Reversing Valve

A four-way directional valve used to reverse a double acting cylinder or reversible motor.

Rotary Actuator

• A device for converting hydraulic energy into rotary motion.
• A hydraulic motor.


An acronym for room-temperature vulcanizing. An RTV adhesive vulcanizes (cures) without the application of heat.


Displacement of the surface of a bearing relative to a fixed point when one raceway is rotated with respect to other raceway.


The rotating assembly of a motor. Usually includes a shaft, fan and rotor core.