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Glossary

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Back-up Ring
Syn: anti-extrusion ring or support ring.
Bi-directional Seal
A seal that prevents leakage from both directions.
Break-out Force
The amount of frictional force required to start a body in motion over a surface.
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Cold Flow
Continued deformation under stress. See “Creep.”
Composite Material
A heterogeneous combination of two or more materials (reinforcing elements, fillers and binders). The combination results in a material that maximizes specific performance properties.
Compression Set
The permanent deformation of a seal after release of a compressive load.
Copolymer
A polymer consisting of two of more different monomers chemically combined.
Creep
The progressive relaxation of a given polymer while under stress. The term cold flow is synonymous with creep.
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Deflection
The overlap in dimension between the seal free height and the gland into which it is installed. Synonymous: squeeze for elastomer or rubber.
Dynamic Seal
A seal required to prevent leakage between opposing surfaces, which are in relative motion.
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Elasticity
The tendency of a body to return to its original shape and dimensions after having been stretched, compressed or deformed.
Elastomer
Any synthetic or natural material which can return rapidly to its original shape after major or minor distortion. Elastic, rubber-like material.
Elongation
Generally referred to as ultimate elongation. Percent increase in original length of a specimen when it reaches its breaking point.
Extrusion
Distortion or flow of part of a seal into an extrusion gap under pressure.
Extrusion Gap
The clearance on the low pressure side between two bodies, which confine the seal.
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Face Seal
A seal that is compressed in a direction parallel to the axis.
Flash
Thin imperfections on the elastomeric portion of a seal, formed by extrusion of the elastomer at the parting lines in the mold cavity.
Flex Cracking
A surface cracking induced by repeated bending or flexing.
Fluid
Either a liquid or gas contained by a seal.
Free Height
The measure of radial height for a radial seal or the axial width for a face seal when the seal is in free-state.
Fretting
A combination of corrosion and wear which occurs when a seal wipes the oxide coating from a shaft sleeve, exposing the base metal to the action of corrosion.
Friction
The force that resists the relative motion of two bodies in contact.
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Gasket
A seal which is used between two relatively static surfaces to prevent leakage. It is made from any deformable material.
Gland
A cavity into which a seal (or O-ring) is installed. It includes the groove and mating surface which together confines the seal.
Gland Cross Section
The radial height of the gland for a radial seal. The axial width of the gland for a face seal.
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Hardness
A material’s resistance to a distorting force. The hardness is measured by the relative resistance of the material to an indentor point. Higher numbers indicate harder material.
Housing
A rigid structure which supports and confines the seal assembly with respect to the shaft.
Hydraulic Seal
A seal normally energized by a rubber or an elastomeric component and designed specifically for hydraulic and pneumatic applications.
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Jacket
The plastic or elastomeric member surrounding the spring.
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Leakage Rate
The quantity of fluid passing through a seal in a given length of time. For compressible fluids, it is normally expressed in standard cubic feet per hour (SCFH), and for uncompressible fluids, in terms of cubic centimeter per unit of time.
Lip Seal
An elastomeric or fluoroplastic seal that prevents leakage in rotary shaft seal applications by employing one or more contact lips to provide a scraping or wiping action on the shaft surface. These seals are commonly called shaft seals, oil seals or rotary lip seals.
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Modulus
Indicative of the stiffness or rigidity of the materials. Modulus is measured in psi (pounds per square inch), and it can be measured in any mode of deformation, i.e., tension (stretching), compression (crushing), flexing (bending), or torsion (twisting).
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OmniFlex
A proprietary perfluoroelastomer material. It has excellent thermal and chemical resistance properties.
O-ring
A toroidal shaped sealing device usually made from rubber or elastomeric material.
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Perfluoroelastomer
A polymeric material which is fully fluorinated and exhibits high chemical resistance.
Permanent Set
Permanent deformation of spring or elastomer upon release of load.
Permeation
The passage of a fluid under pressure through a solid material by diffusion.
Polymer
A material formed by the joining together of many (poly) units (mer) of one or more monomers. Synonymous: elastomer or rubber.
Porosity
Quality or state of being porous.
PTFE
Polytetrafluoroethylene.
PV Factor
An arbitrary term which is the product of face pressure and relative sliding velocity. The term is normally considered to provide some measure of severity of service, and thus relates to a seal’s wear life. The units customarily used are “psi-fpm.”
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Radial Seal
Seals that are compressed in a radial direction. Radial seals are used as rod and piston seals and are usually dynamic, although they may occasionally be static.
Rubber
See “Elastomer.”
Run-out
Twice the distance which the center of a shaft is displaced from the axis of rotation. It is expressed in “TIR” (total indicator runout/reading).
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Scraper
A device employed to keep out dirt or other foreign matter.
Seal
A device designed to prevent the passage of a medium (fluid or solid).
Seal Cavity
The annular area into which a seal is installed.
SES
Spring energized seal. Shrinkage – A decrease in size. For PTFE seals, cold temperature shrinkage must be considered when designing the spring.
Spring
A machine element capable of restoring energy and releasing it. (The elastic member of the OmniSeals.)
Static Seal
A seal between two surfaces which have no relative motion.
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Tensile Strength
Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material.
Thermal Expansion
Expansion caused by increase in temperature.
Torque
The tendency of a force to produce rotation about an axis. Frictional torque equals frictional force times the radius of rotation.
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Uni-directional Seal
A seal that prevents leakage from only one direction.
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Vacuum
An enclosed space that is occupied by a gas at less than atmospheric pressure.
Vulcanization
A thermo-setting reaction involving the use of heat and pressure, resulting in greatly increased strength and elasticity of rubber-like materials.
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Weepage
A minute amount of liquid leakage by a seal.
Wiper Ring
See “Scraper.”
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This is a printed version of Oil-Seals.info of ERIKS nv.
© ERIKS nv, 2016.