Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
ABRASION:
Progressive wearing away of material.
ABRASION RESISTANCE:
The ability of a material to resist mechanical wear.
ACCELERATED SERVICE TEST:
Any set of test conditions designed to reproduce in a short time the deteriorating effect obtained under normal service conditions.
ACTIVE INHIBITOR:
A type of galvanic corrosion inhibitor added to packing. It acts as a sacrificial anode, corroding in preference to the surrounding metal. Zinc dust is added to the surface of some packing materials as an active inhibitor. See also “Galvanic Corrosion”. Compare with “Passive Inhibitor”.
ACTUATE:
To cause movement of a valve stem either by raising, lowering, or turning it.
ACTUATOR:
A device, attached to a valve, which moves the stem, usually by means of a motor or pneumatics. A valve fitted with an actuator is usually referred to as a control valve.
ADHESION:
The clinging, binding or sticking of two material surfaces to one another, such as rubber to rubber, rubber to metal, or rubber to cloth. It also refers to the bond strength between two surfaces.
AGING:
Undergo changes to physical properties with lapse of time.
AMBIENT TEMPERATURE:
The temperature of the surrounding environment.
ANCHOR:
Terminal point or fixed point from which directional movement occurs.
ANGLES:
L-Shaped steel member used either as a duct flange or as the fastening connection of an expansion joint. Angles are also used for bolting the joint to the mating flange surfaces of the duct work or adjacent equipment.
ANGULAR MOVEMENT:
Movement which occurs when one flange of the expansion joint is moved to an out of parallel position with the other flange. Angular movement is measured in degrees.
ANSI:
Abbreviation for “American National Standard Institute”.
ANTI-EXTRUSION RING:
A ring of packing used at one or both ends of a packing set to prevent extrusion of the packing into clearances. Also called a “Bull Ring.” See also “End Ring” and “Junk Ring.”
AOV:
Abbreviation for “Air Operated Valve”, a pneumatically actuated valve.
API:
Abbreviation for American Petroleum Institute.
AQUEOUS SOLUTIONS:
Any fluid solution containing water. See further discussion under “pH.”
ARAMID:
A family of polymers used in a fibrous form as packing materials. Kevlar® is a DuPont trade name for an aramid fiber known for its excellent abrasion resistance, high tensile strength, and its characteristic deep yellow color. Nomex® is the DuPont trade name for another type of aramid fiber.
ASME:
Abbreviation for American Society of Mechanical Engineers.
ASSEMBLED SPLICE:
A splice that is constructed of multi layers of materials and connected by use of elastomeric cements, adhesives, etc.
ASSEMBLED SPRING INSIDE DIAMETER:
The inner diameter of the garter spring, with the ends securely joined.
ASTM:
Abbreviation for American Society for Testing and Materials.
AUTOCLAVE:
In the rubber sheet manufacturing industry, the device used to vulcanize (cure) elastomers. Typically the autoclave is drum-shaped, open on one end, and is steam-heated.
AXIAL:
In the direction of a shaft or stem axis.
AXIAL CLEARANCE:
The gap between the toe face to the head section and the inside surface of the inner case.
AXIAL COMPRESSION:
The dimensional shortening of an expansion joint parallel to its logitudinal axis. Such movement being measured in inches or millimeters and usually caused by thermal expansion of the piping/ducting system.
AXIAL EXTENSION:
The dimensional lengthening of an expansion joint parallel to its logitudinal axis. Such movement being measured in inches or millimeters.
AXIAL SURFACE ROUGHNESS:
Surface roughness of a shaft measured in a direction parallel with the centerline axis.
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B
BACK-UP BARS:
Metals bars used for the purpose of clamping a rectangular/square expansion joint to mating ductwork.
BAFFLE/ FLOW LINER:
A metal shield that is designed to protect the expansion joint from the abrasive particles in the gas stream and to reduce flutter caused by air turbulence in the gas stream. Baffles/Flow Liners may be welded or bolted into position.
BANBURY MIXER:
A specific type of internal mixer used to mix rubber or plastic compounds with fillers and other ingredients.
BEATER ADD (BEATER SATURATED):
A manufacturing process for making non-metallic sheet that employs a paper-making process using Fourdrinier or cylinder-type paper machines.
BELLEVILLE WASHER:
A disc spring washer used to live-load a packing gland.
BELLOWS:
That portion of an expansion joint which accommodates the movement of the joint convoluted or flat.
BELT TYPE EXPANSION JOINT:
An expansion joint in which the flexible bellows portion of the joint is made flat and bolted or clamped to metal adapter flanges or frames.
BENCH TEST:
A modified service test in which the service conditions are approximated using laboratory equipment not necessarily identical with the equipment in which the product will be employed.
BEVEL CUT:
An angled cut at the seam (or joint) of a packing ring.
BILLET:
A large rod of PTFE; the initial stage of manufacture for skive PTFE.
BLEMISH:
A mark, deformity, or injury which impairs the appearance.
BLISTER:
A raised spot on the surface or a separation between layers, usually forming a void or air-filled space in the gasketing material.
BLOCKING AGENT:
A coating applied to braided packing to fill the area between the fibers, blocking the passage of media through the body of the braid, and improving its sealing characteristics. This may be a grease, an oil, or a PTFE dispersion.
BODY:
See “Valve Body”.
BOLT HOLE PATTERN OR DRILL PATTERN:
The systematic location of bolt holes in the mating flanges and expansion joint flanges where joint is to be bolted.
BOLT IN BAFFLE/FLOW LINERS:
A baffle that is designed to be bolted to the breach flange. NOTE: Bolt in baffles/flow liners require the use of a seal gasket.
BOLT TORQUE:
The amount of twisting or turning effort (expressed as Ft- Lb or N-m) required to turn the nuts on a gland follower. The load that the gland follower exerts on a valve packing set can be expressed in terms of a specific bolt torque.
BONNET:
See “Valve Bonnet”.
BOOT OR BELT:
The flexible element of an expansion joint usually consisting of rubber and rubbercoated fabric.
BORE DIAMETER:
The outside dimension of the annular space that packing is inserted into. Also called the stuffing box bore.
BRAID:
Yarns or filaments woven together to form a hollow or solid structure. A braid may have a round (Braid over Braid), square (Simple Crossing Pattern), or LATTICE (Interlocking) weave pattern. Braids may have round, square, or rectangular cross-sectional shape.
BRAID OVER BRAID:
A type of braiding construction in which a series of round braided layers are braided on top of one another.
BRAID OVER CORE:
A type of braiding construction in which yarns are round braided over a core. Cores may be composed of an elastomer extrusion, a plastic compound extrusion, another braid, or other materials.
BRAIDER:
A mechanical device which interweaves yarns to produce a braid.
BREACH FLANGE OR DUCT FLANGE:
The portion of the duct system, usually an angle or a channel that interfaces with the flange of the expansion joint.
BREACH OPENING:
The distance between the mating duct flanges in which the joint is to be installed.
BREAK-IN LUBRICANT:
A lubricant added to the surface of braided packing. Break-in lubricants are used to protect the packing from charring during the initial start-up of rotating equipment, such as pumps and mixers.
BUBBLE SEALING:
A sealing level that does not exceed 1.0 x 10-4 atm cc/sec of Helium.
BULK DIPPING:
An economical method for applying coating to a packing material simply by dipping a container of braid into a tank containing the coating material.
BULL RING:
See “Anti-Extrusion Ring”.
BURST:
A rupture caused by internal pressure.
BUSHING:
A metallic or carbon ring used to take up excess space in a stuffing box.
BUTT CUT:
A straight cut at the seam (or joint) of a packing ring.
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C
CALENDER:
1) A step in the production of braided packing where a braided material is fed through rollers to squeeze it to its finished size. 2) A machine which is used to calender a braid.
CARBONIZATION:
The reduction of a material to carbon.
CASE OD SEALER:
A coating applied to the case OD to prevent leakage between the seal case and the housing bore.
CAVITATION:
An undesirable phenomenon that sometimes occurs in pumps, in which small vapor bubbles are created in the area of the impeller. As these vapor bubbles move along the vanes of the impeller to an area of higher pressure, they rapidly collapse. This collapse or “implosion” is so rapid that it may be heard as a rumbling noise or felt as vibration. The forces generated as a result of cavitation may damage the impeller or even the packing set.
CENTERING RING (OR GUIDE RING):
A solid piece of metal used on the OD of a gasket winding in order to center the gasket properly on the sealing surface by locating the ring against the studs in the connection. The ring also acts as a compression limiter to prevent overcompression of the winding.
CENTRIFUGAL PUMP:
A type of pump which relies on the rotation of an impeller to generate pressure and cause flow.
CHECKING:
The short, shallow cracks on the surface of a rubber product resulting from damaging action or environmental conditions.
CHEVRON PACKING:
Also known as Vee Packing and Stack Packing, an automatic Hydraulic and Pneumatic seal designed for sealing rods, rams, pistons, and plungers. Consisting of a male and female adapter and at least (3) CHEVRON “vee” rings which utilize a distinct hinge area to allow automatic reaction to pressure. CHEVRON-type packing are lip-type seals and are gland sensitive.
CIRCUMFERENTIAL SURFACE ROUGHNESS:
Surface roughness of a shaft measured in a direction (plane) normal to the centerline axis.
CLAMP BARS:
Same as back-up bars.
CLOTH BOTH SIDES (CBS):
Rubber sheet consisting of a ply of fabric or cloth on each surface. CDS: Cloth on just one side.
CLOTH INSERTED (CI):
Rubber sheet containing one or more plies of fabric or cloth, in which the fabric is completely covered with rubber.
COCKED ASSEMBLY:
An installation in which the plane of the outside seal face is not perpendicular to the shaft axis.
COIL:
One turn of the coiled wire garter spring.
COKER GASKET:
Gasket for the coke unit in petroleum refineries.
COLD FLOW:
Permanent and continual deformation of a material that occurs as a result of prolonged compression or extension at or near room temperature.
COMPRESSED HEIGHT:
The height of a packing ring or packing set after it has been compressed in the stuffing box.
COMPRESSED SHEET:
A gasketing material primarily containing fibers, rubber and fillers, manufactured on a special calender (known as a “sheeter”) in such a manner that the compound is caused to build up under high load as an oriented sheet on one roll of the sheeter.
COMPRESSIBILITY:
The quality or state of being compressible. In the case of gasketing, it is the percent loss of thickness when subject to a given load.
COMPRESSION LIMITER:
Ring used in conjunction with a seal to control or limit compression of the seal.
COMPRESSION PACKING:
A deformable material used to prevent or control the passage of a pressurized fluid between surfaces that move in relation to each other.
COMPRESSION SET:
The deformation that remains in the gasketing after it has been subjected to, and released from, a specific compressive stress for a definite period of time at a prescribed temperature (Compression Set measurements are for the purpose of evaluating creep and stress relaxation properties of elastomeric constructions.).
COMPRESSIVE STRESS:
Force per unit area compressing (squeezing) the seal.
CONFLAT FLANGE:
A common vacuum industry flange.
CONTACT APPROACH ANGLE:
Synonym: Angle, Outside Lip.
CONTACT LINE:
The line of intersection between the outside and inside lip surfaces of a radial lip seal. In a cross-sectional view, this intersection is illustrated as a point.
CONTACT LINE HEIGHT:
The axial distance from the outside seal face to the lip contact line.
CONTACT WIDTH:
The width of the lip contact area of a radial lip seal, measure in the axial direction.
CONTINUOUS OPERATING TEMPERATURE (COT):
Actual operating temperature of service.
CORNERS:
Molded, formed, or radius belt corners of rectangular/square expansion joint.
CORROSION INHIBITOR:
An ingredient added to packing, which decreases or eliminates the possibility of galvanic corrosion in the stuffing box. Corrosion inhibitors may be classified as either passive or active. See “Active Inhibitor”, “Passive Inhibitor”, and “Galvanic Corrosion”.
CORRUGATED:
Formed into alternating peaks and valleys; typically limited to sheet metal 0.024″ and thinner.
COVER:
The outermost ply of material of an elastomeric expansion joint.
CRACK:
A sharp break or fissure in the sealing element.
CRACKING:
A sharp break or fissure in the surface, generally due to excessive strain.
CREEP RELAXATION:
A transient stress-strain condition in which strain increases concurrently with the decay of stress. More simply put, it is the loss of tightness in a gasket, measurable by torque loss.
CROSS-SECTION:
1) The view of a part as if it were cut to show its internal structure. 2) The distance between the shaft or stem surface and the bore of a stuffing box. See also “Packing Space”. 3) The shape of a packing ring at a cut. A packing ring could have a square, rectangular, or round crosssection.
CRYOGENIC:
Of or relating to a very low temperature.
CUP AND CONE:
The shape of certain types of die-formed ring sets. In a “cup and cone” set the rings have conical surfaces that nest into one another.
CUP PACKING:
A specific type of hydraulic or pneumatic sealing element which seals primarily on it’s outside diameter.
CURE:
The act of vulcanization. (Also see Vulcanization)
CUT:
A deep discontinuity in the seal material whereby no material is removed.
CUT-RING SET:
A braided material cut into individual rings for a specific stem/stuffing box size and packaged as a set.
CYCLE AND ADJUST PROCEDURE:
A procedure used to consolidate a packing set after it has been installed in a stuffing box. This procedure helps to reduce the amount of gland load relaxation that occurs after the valve has been put into service.
CYCLETIGHT®:
VSP Technologies’ family of “spring loaded,” corrugated insert ePTFE gaskets. Enhances the handleability and performance capabilities of conventional expanded PTFE gaskets.
CYCLETIGHT® TYPE 7 MANWAY GASKET:
Semi-metallic expanded PTFE gasket designed for use in general purpose tank car manway dome lids. VSP Technologies’ patented construction allows the CycleTight® gasket to fit securely into the manway cover to provide low assembly torque and multiple reuses across a broad range of chemical services.
CYLINDER:
A device which converts fluid power into linear mechanical force and motion. It usually consists of a moveable element such as a piston and piston rod, plunger rod, plunger, or ram, operating within a cylindrical bore.
CYLINDER BORE:
The internal diameter of the cylinder.
CYLINDER DOUBLE ROD:
A cylinder with a piston rod extending from each end.
CYLINDER, RAM-TYPE:
A cylinder in which the piston and piston rod are one and the same. These cylinders are single-acting and are mounted vertically: the weight of the load retracts the cylinder.
CYLINDER SINGLE ROD:
A cylinder with a piston rod extending from one end.
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D
DEFORMATION:
A stress induced change of form or shape.
DENSITY:
The ratio of the mass of a body to its volume, expressed as Lb/Ft3 or gm/cc. It is common for die-formed graphite foil rings to be produced to a specific density.
DESIGN PRESSURE/VACUUM:
The pressure or vacuum condition that exists during system start-up and/or shut-down operations. During this cyclic phase in the system, both pressure and vacuum conditions may occur.
DESIGN TEMPERATURE:
The maximum or most severe temperature expected during normal operation caused by equipment failure. (See Excursion Temp.)
DIAPHRAGM SHEET:
PTFE or sheet rubber (generally fabric-reinforced) from which flat diaphragms are cut.
DIE CUT:
Shaped articles cut with a die from a sheet of material.
DIE FORMING:
A manufacturing process in which braid or graphite foil is compressed in a mold to form a ring.
DIELECTRIC STRENGTH:
The measure of a product’s ability to resist passage of a disruptive discharge produced by an electric stress described in volts/mil (1 mil = 0.001″).
DIN:
Abbreviation for Deutsches Institut für Normung. English translation is German Industry Standard - it is the European equivalent to ASTM.
DISCHARGE PRESSURE:
The fluid pressure measured on the discharge (or outlet) side of the pump where the fluid exits the volute.
DISHED DIAPHRAGM:
A molded diaphragm in which the entire center is depressed below the plane of the rim.
DRILL PATTERN:
The systematic location of bolt holes on the mating and expansion joint flange through which the expansion joint will be attached.
DRUM CURE:
A method of vulcanizing rubber in which the product is wrapped around a drum and cured in hot air or steam, usually with a separator or wrapping jacket.
DUCT ID:
The inside dimension of the ductwork measured from the duct walls prior to any form of coating.
DUCTILITY:
The ability to be drawn. Example: The stretching of metal wire to a smaller cross-section.
DUROMETER HARDNESS:
An arbitrary numerical value measuring the resistance to indentation (without puncturing) of the indentor into the surface or rubber.
DYNAMIC RUNOUT:
Twice the distance the center of the shaft is displaced from the center of rotation and expressed in TIR. That runout to which the seal lip is subjected due to the outside diameter of the shaft not rotating in a true circle. Synonym: Shaft Runout.
DYNAMIC SEAL:
A seal required to prevent leakage past parts which are in relative motion. The opposite of static seal.
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E
E-COATING:
A coating process where an electric charge is used to bond the paint to the metal outer ring for Garlock spiral wound gaskets. The result is a smooth, drip-free finish with superior chip resistance. The process is also environmentally friendly, as no ozone-depleting propellants are used in the process.
ECCENTRICITY:
The distance that the central axis of a shaft is offset from the center of the stuffing box through which it passes.
ELASTIC LIMIT:
The limiting extent to which a body may be deformed and yet return to its initial shape after removal of the deforming force.
ELASTOMER:
An elastic rubber-like material which, in the vulcanized state and at room temperature, can be stretched repeatedly to at least twice its original length. Upon release of the stress, this material will immediately return to approximately its original length.
ELONGATION:
The increase in length expressed numerically as a fraction or percentage of the initial length.
EMISSIONS:
Gaseous or liquid leakage given off by a piece of equipment. This usually refers to volatile organic hydrocarbons monitored by government agencies. It is typically expressed in parts per million volumetric (ppmv, or simply ppm).
END PLAY:
A measure of axial movement encountered or allowed, usually in reference to the shaft on which the seal lip contacts.
END RING:
A ring used at the top or bottom of a packing set, usually functioning as a wiper ring and/or an anti-extrusion ring. See also “Anti-extrusion Ring”, “Junk Ring”, and “Wiper Ring”.
EPA:
Abbreviation for “Environmental Protection Agency”, the US government agency responsible for enforcing the regulations imposed by the Clean Air Act Amendment.
EPA METHOD 21:
A method established by the EPA for performing emissions measurements on equipment such as valves, pumps, and flanges.
EXCLUSION DEVICE:
A device capable of excluding contaminating particles and fluids that would otherwise be dragged back into the primary sealing area of the equipment.
EXCURISION TEMPERTURE:
The temperature the system could reach TEMPERTURE: during an equipment failure such as an air heater failure. Excursion temperature should be defined by maximum temperatures and time duration of excursion.
EXPANSION:
The increase in any linear dimension or volume.
EXTERNAL ARCH CORNER:
An expansion joint corner with the arch formed outwardly that is designed primarily for pressure service, generally used in conjunction with a rectangular or square expansion joint.
EXTERNAL PRESSURE:
Pressure (Lbs./Sq. Inch) exerted on the OD of a seal.
EXTRACTION TEST:
A test involving the separation of certain components from a solid by dissolving them in a liquid solvent under suitable conditions.
EXTRUSION:
The distortion, under pressure, of a portion of a seal into the clearances between mating metal parts.
FABRIC FINISH:
See “Fabric Impression.” The term “Cloth Finish” is used interchangeably.
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F
FABRIC IMPRESSION:
A pattern in the rubber surface formed by contact with fabric during vulcanization (usually during Drum Curing).
FATIGUE:
The weakening or deterioration of a material occuring when a repetition or continuous application of stress causes strain.
FIELD ASSEMBLY:
A joint that is assembled at the jobsite due to its size ( too large to ship ) or the location of the breach opening makes it more practical to install in sections.
FILLER:
Any compounding material, usually in powder form, added to gasketing materials either to improve quality or reduce cost.
FINISH (see RMS):
Surface condition of materials for metals, measured in terms of RMS.
FLANGE:
Rim or edge projecting at right angles to provide strength, or a means of attachment to another part.
FLANGE JOINT:
A joint formed by two abutting flanges.
FLANGE PACKING:
See Hat Packing.
FLANGES:
That part of an expansion joint used for fastening the joint into the system. Can be either metal or same materials as the bellows.
FLEX LIFE:
The relative ability of a rubber article to withstand cyclical bending stresses.
FLOW DIRECTION:
Direction of media (fluid, gas, air, etc.) movement through the system.
FLOW LINER (BAFFLE):
A metal shield that is designed to protect the abrasive media in the stream and to reduce flutter caused by the air turbulence in the gas stream. Flow Liner/Baffles may be welded or bolted into position.
FLOW METER:
A device used to measure the flow rate of a fluid through a pipe. In packing applications a flow meter may be used to measure the amount of flushing fluid that is entering and/or leaving the stuffing box.
FLUID SIDE:
The side of the seal which in normal use faces toward the fluid being sealed.
FLUSH PORT:
A hole in the side of a stuffing box through which a cleansing or lubricating fluid is injected.
FLUSHING FLUID:
A clean liquid (usually water) which is injected through a flush port to exclude solid particles from the stuffing box area and minimize abrasive wear. A flushing fluid might also be used to cool the packing in a high temperature application, or to keep air from being drawn into a pump in a suction application.
FLUTTER:
The action that occurs on the joint body caused by turbulence of the system media or vibration set-up in ducting system.
FOLLOWER:
See “Gland Follower”.
FORCE POUNDS:
The total load required to deflect an expansion joint a distance equal to the maximum rated movement of the product.
FOREIGN MATERIAL:
Any extraneous material such as dirt, sand or metal that should not normally be present in or on a product.
FPM:
Abbreviation for “Feet per Minute”, a measure of the surface speed of a rotating shaft.
FRAME:
The complete angle iron or plate frame to which belt of bellows portion of the expansion joint is attached.
FRICTION:
Resistance to motion due to the contact of surfaces which normally generates heat.
FRICTION COATING:
A rubber covering applied to the weave of a fabric simultaneously with impregnation.
FRICTION FACTOR:
An empirically determined factor used to estimate the frictional force generated by the packing on a valve stem. It is important to note that this is not the same as “Coefficient of Friction”.
FSA:
Fluid Sealing Association, an American-based trade association for the mechanical packing industry.
FSA (FLUID SEALING ASSOC.):
The name of the American-based trade association for the Mechanical Packing Industry.
FUGITIVE EMISSIONS:
An unintentional gaseous or liquid leakage given off by a piece of equipment. See also “Emissions”.
FULL-FACE GASKET:
A gasket covering the entire flange surface and including bolt holes.
FUNCTIONAL LIP DIAMETER:
The apparent inner diameter of the seal when the seal case is concentric with the outer diameter of the sizing mandrel in an air gage, light box, or similar inspection equipment.
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G
GALVANIC CORROSION:
An electrochemical reaction that may occur between a metal and a more chemically noble material such as another metal, carbon, or graphite. When both materials are immersed in an electrically conductive media called an electrolyte, a galvanic cell is formed and current flows between the two materials. The least noble material (called the anode) will corrode, while the more noble material (the cathode) will not.
GARTER SPRING:
A helically coiled wire with its ends connected to form a ring. It is used in tension for maintaining a radial sealing force between element of a radial lip seal and a shaft.
GASKET:
A deformable material, which, when clamped between essentially stationary faces, prevents the passage of matter through an opening or joint.
GASKET SPACER:
A gasket material cut to fit in a stuffing box between braided packing rings. Gasket spacers may be used to provide protection against abrasive particles, to increase the pressure resistance of some packing sets, or to reduce the flow of fluid through the body of the braid.
GASKETING:
Material in bulk form from which gaskets may be cut.
GAUGE:
The thickness of a material; also the device used to measure material thickness.
GLAND:
See “Packing Gland”.
GLAND FOLLOWER:
A part which protrudes into a stuffing box to compress a packing set or packing ring.
GLAND LOAD:
The amount of load applied to a packing set. This may be expressed in terms of force (Lbs., N) or in terms of pressure (psi, kPa).
GLAND PRESSURE:
The amount of pressure applied to a compression packing set by the gland follower, usually expressed in psi or kPa.
GLAND STUD:
A threaded rod or eye bolt, extending from a valve or pump body, that is used to compress a packing set.
GROOVE:
The area in which a hydraulic seal is contained for the purpose of sealing against a rod, or cylinder wall or an annular seal cavity.
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H
HAND WHEEL:
A wheel located at the top of a manually operated valve that is used to actuate the valve stem.
HAT (FLANGE) PACKING:
An old form of sealing rods, which seals on the ID only.
HEAD:
The pressure at any point in a fluid can be thought of as being caused by a vertical column of the liquid that, due to its weight, exerts pressure at the point in question. The height of this column is called the “static head” (or sometimes simply “head”) and is expressed in terms of feet or meters of liquid.
HEAT EXCHANGER:
A piece of equipment designed to transfer thermal energy from one media to another. The unit is typically a long cylindrical body with multiple tubes passing within the body. Media of one temperature flows within the body but external to the tubes, while media of another temperature flows within the tubes, thus allowing thermal energy to exchange without cross-contamination of the products.
HEEL SECTION:
The portion of a lip seal which is attached to the seal case and bounded by the flex section and the outside face.
HELICAL MOTION:
The circular, screw-like, up and/or down motion of a rod or valve stem.
HELICOFLEX® SEAL:
Metal seal composed of a helical, wound spring with a single or double jacket wrapped around the spring. Cross-section of the seal is circular and various shapes and sizes can be created using different jacket wrappings.
HELIUM SEAL:
A sealing level that does not exceed 1.0 x 10-9 atm cc/sec of Helium.
HELIX CONTACT WIDTH:
The axial width of that portion of the contact surface of a helix seal which is formed by the helical ribs. It is equal to the total axial width of the contact surface minus the width of the static lip.
HELIX SEAL RIB SEAL:
The angle formed by the leading edge of the rib and a line perpendicular to a plane tangent to the outside lip surface at the centerline of rib base.
HELIX SEAL RIB WIDTH:
The maximum width of a helical rib measured perpendicular to the ribOs longitudinal axis.
HOMOGENEOUS:
Of uniform composition throughout.
HOUSING BORE:
A cylindrical surface which mates with the outside diameter of the outer seal case.
HYDRODYNAMIC SEAL:
A dynamic sealing device which utilizes the viscous shear and inertia forces of the fluid; imparted by a helically grooved or ribbed seal lip, to generate a pressure differential that opposes fluid flow.