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Glossary of Terms - All Terms

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Glossary Subsets


The Society of Automotive Engineers

SAE O-Ring

Refers to a style of threaded connection that employs straight thread to secure the fitting and an o-ring to provide sealing. This style of connection is very poplular for use in hydraulic systems and can be removed and reinstalled numerous times without damaging the sealing ability of the connection. Tapered pipe thread is actually damaged to make a fluid tight seal. Vibration and repeated connection of tapered pipe threaded connections will always resulin in leaks.

Safety Switch

A manually-operated disconnecting switch which is horsepower and current rated, it disconnects all power lines simultaneously.

SCFM (Standard Cubic Feet Per Minute)

Unit of measure representing volume of gas flow.

Saybolt Universal Seconds (SUS)

A measure of viscosity, the time required for a given fluid to flow through a standard orifice.

Self-Aligning Bearing

A bearing which can accommodate angular misalignment.

Separable Bearing

A bearing that may be separated completely or partially into its component parts.


A name given to substances having only moderate power of transmitting electricity.

Self-Locking Collar

A ring having a recess on one side which is eccentric in relation to the bore and fits over an equally eccentric extension of the inner ring insert bearing. The collar is turned in relation to inner ring until it locks and then secured to shaft by tight


• The order of a series of operations or movements.
• To divert flow to accomplish a subsequent operation or movement.

Sequence Valve

A pressure operated valve which diverts flow to a secondary actuator while holding pressure on the primary actuator at a predetermined minimum value after the primary actuator completes its travel.


In line with the load.

Service Factor

• A safety factor designed and built into some motors which allows the motor, when necessary, to deliver greater than its rated horsepower.
• Also used as a factor when sizing system components, based on application, to achieve design hors


A system consisting of an amplifier, actuator, and feedback element. Servos tend to control one or a combination of the following variables: position, velocity and torque.


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

Servo Mechanism

A mechanism subjected to the action of a controlling device which will operate as if it were directly actuated by the controlling device, but capable of supplying power output many times that of the controlling device, this power being derived from an external and independent source.

Servo Valve

• A valve which controls the direction and quantity of fluid flow in proportion to an input signal.
• A follow valve.


The hardening or solidification of an initially liquid plastic material by chemical and/or physical action.

Shaft Fit

Amount of interference or clearance between the bearing inside diameter and shaft bearing seat outside diameter.

Shear Strength

The sliding force required to break a bond, divided by its cross-sectional area.


• A metal formed washer attached to the outer ring and set so it rides close to, but not contacting, the inner ring.
• Helps retain lubricant and prevent contamination.
• Does not keep out fine particles like a seal does.

Short Circuit

A fault in an electric circuit or apparatus due usually to imperfect insulation, such that the current follows a by-path and inflicts damage or is wasted.


A device to bypass power away from a line.


• The side of a ball race.
• A surface in a bearing application or shaft which axially positions a bearing and takes the thrust load.


A command or indication of a desired position or velocity.

Single Acting Cylinder

• A cylinder in which hydraulic energy can produce thrust or motion in only one direction.
• Can be spring or gravity returned.

Silicon Controlled Rectifier (SCR)

Converts AC to DC. Used to supply DC power to drive DC motors.

Single Phase

A circuit that differs in phase by 180 degrees. Single phase circuits have two conductors, one of which may be a neutral, or three conductors, one of which is neutral.

Single Row

A bearing with one row of rolling elements.


Internal leakage of hydraulic fluid.


• To cut, split or pare away outer layer of a flexible hose.
• Also refers to a type of cut for belting or other rubber products.


A spiral of conducting wire, wound cylindrically so that when an electric current passes through it, its turns are nearly equivalent to a succession of parallel circuits, and it acquires magnetic properties similar to those of a bar magnet.


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

Snap Ring

• A removable ring used to axially position a bearing or component in a housing.
• May also be used as a means of fastening a shield or seal in a bearing.

Specific Gravity

The density of any material divided by that of water at a standard temperature.


A large momentary increase in the amount of voltage or amperage supplied to the circuitry.

Spherical Roller Bearing

A self-aligning rolling bearing with convex rollers or concave rollers as rolling elements. With convex rollers, the outer ring has spherical raceway. With concave rollers, the inner ring has spherical raceway.


• A device used to control the electrical power to motors.
• Provides overload protection as required by the NEC.
• Can be operated manually, electrically, or by automatic pilot devices.
• A starter has two basic parts -

Star Connection

The same as a ""Y"" or ""Wye"" connection. This three-phase connection is so called because, schematically, the joint of the ""Y"" points looks like a star.

Standard Bearing

A bearing which conforms to the basic plan for boundary dimensions of metric or inch dimensions.


A term loosely applied to almost any moving cylindrically shaped part of a hydraulic component which moves to direct flow though the component.

Starting Amps

The maximum current drawn by the motor during the starting period.

Static Load

A load exerted on a bearing not in motion.


The Society of Tribologists and Lubrication Engineers, who are involved with friction, wear, and lubrication. Formerly known as ASLE, the American Society of Lubrication Engineers.


A coarse filter for trapping large particles.


• The length of travel of a piston or plunger.
• To change the displacement of a variable displacement pump or motor.


The stationary part of a motor. A permanent magnet DC motor holds its magnets in the stator.


The basic surface upon which the adhesive is applied and to which it is expected to adhere.

Suction Line

The hydraulic line connecting the pump inlet port to the reservoir.


An auxiliary mounting for a hydraulic component providing a means of connecting piping to the component.


A reservoir.

Surface Preparation

Physical and/or chemical pretreatments to enhance the adhesive strength of an adhesive to be applied to a specific surface.


See charge


A momentary rise of pressure in a circuit.

Surge Suppressor

• A device that suppress voltage transients that can occur on the AC line.
• A metal oxide varistor (MOV).


Saybolt Universal Seconds. A measure of viscosity, the time required for a given fluid to flow through a standard orifice.

Swash Plate

A stationary plate in an axial type piston pump or motor which causes the pistons to reciprocate as the cylinder barrel rotates.