Glossary of Terms

Glossary of Terms FSA Knowledge Series

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Abstract Piping Plans This Fluid Sealing Association Knowledge Series training presentation provides a definition of terms related to end face mechanical seals.

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Glossary of Terms - A A abrasive wear - Wear occurring by the mechanical action of suspended abrasives or by abrasives that crystallize on the atmospheric side of the seal.

ANSI - American National Standards Institute.

air side - That side of an elastomeric shaft seal which in normal use faces away from the fluid being sealed. anti-extrusion ring - A close clearance ring installed on the low-pressure side of a secondary seal, in order to prevent extrusion of the sealing material. anti-rotation device - A device such as a key or pin, used to prevent rotation of one component relative to an adjacent component in a seal assembly.

ASME - American Society of Mechanical Engineers. asperities - Minute imperfections on the sealing face of the primary ring or surface of the mating ring which are the result of normal surface-processes finishing. Imperfections or surface irregularities that result from the formulations or ingredients used in elastomeric seals. auxiliary equipment - Additional components used in conjunction with a seal, such as environmental controls.

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Glossary of Terms - B B back-to-back seal configuration – Dual seal in which both of the flexible elements are mounted between the mating rings and the sealed fluid is on the ID of the inner seal and the barrier or buffer fluid is on the OD of the inner and outer seal. back-up ring - See anti-extrusion ring. balance diameter - That diameter of a face seal at which the resultant hydraulic force is considered to be acting. This force is obtained from area integration of the pressure profile which exists on the fore- and-aft surfaces of the axially movable portion of the seal assembly. balanced seal - A mechanical seal configuration in which the fluid closing forces have been modified through seal design.

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Glossary of Terms - B balance ratio - The ratio, sometimes expressed as a percentage, of the seal face area exposed to closing force by hydraulic pressure in the seal chamber, to the total sealing face area.

The balance diameter of the seal is used to calculate the ratio. The balance diameter differs based on the design of the seal. It may be determined in the laboratory for bellows seals.

For pusher seals pressurized at the outside diameter the balance ratio may be defined by the simplified equation: B=

𝑂𝐷2 − 𝐵𝑂𝐷2 𝑂𝐷2 − 𝐼𝐷 2

For pusher seals pressurized at the inside diameter the balance ratio may be defined as: B=

𝐵𝐼𝐷2 − 𝐼𝐷 2 𝑂𝐷2 − 𝐼𝐷 2

Where: OD = outside diameter of the seal face ID = inner diameter of the seal face BDO = balance diameter of seal pressurized on the outside diameter BDI = balance diameter of seal pressurized on the inside diameter.

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OD

BID

ID BOD

Glossary of Terms - B barrier fluid - Externally supplied fluid at a pressure above the pump seal chamber pressure, introduced into an Arrangement 3 seal to completely isolate the process liquid form the environment.

Belleville disc washer - A washer which has a slightly conical shape and acts as a spring when compressed axially.

bellows (welded metal) assembly - A series of bellows plates alternately welded together at their inner and outer edges. bellows (metal) convolution - In a welded bellows, an assembly of two formed plates or diaphragms, welded at either the inner diameters or the outer diameters. In a formed bellows, a one-piece, thin- walled, single-ply or multiple-ply, ring like member having a deep fold or corrugation, generally of U- shaped section. bellows damper - A device used with metal bellows seals for reducing vibration. bellows diaphragm - See bellows plate. bellows effective span - That portion of the metal bellows span which is affected by the hydraulic pressure.

Typically defined by the area between the bellows plate outer diameter and the balance diameter. bellows pitch - The distance between convolutions on a metal bellows at the bellows’ working length.

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Glossary of Terms - B bellows plate - A single, thin, metallic disk or washer. bellows seal (elastomeric) - A type of mechanical seal which uses an elastomeric bellows, with or without a coil spring, for secondary sealing and spring loading. bellows seal (metal) - A type of mechanical seal which uses a flexible metal bellows to provide secondary sealing and spring loading. bellows seal (PTFE) - A type of mechanical seal which uses a PTFE bellows with multiple convolutions in conjunction with a coil spring for secondary seal and spring loading. bellows span - The total radial cross-section of a metal bellows. One half of the difference between the inner and outer diameters. bi-rotational seal - A rotary shaft seal which will seal regardless of the direction of shaft rotation. blister - A raised surface or bubble that forms on the surface of a seal face or elastomeric secondary seal material. blistering - A term used to describe a form of damage to carbon graphite seal surfaces. Suspected to be caused by a rapid temperature rise at the seal face after the carbon graphite has become impregnated with a viscous fluid such as a SEA #10 oil.

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Glossary of Terms - B boundary lubrication - A condition of lubrication where the seal faces are in solid contact though separated by adsorbed surface films. breakaway torque - See starting torque. buffer fluid - Externally supplied fluid, at a pressure lower than the pump seal chamber pressure, used as a lubricant and/or to provide a diluent in an Arrangement 2 seal. bypass - An environmental control where the product is piped from the pump casing to the seal chamber, or from the seal chamber to the pump inlet, to cause a fluid flush of the seal chamber.

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Glossary of Terms - C C carbonization - Oxidation of a hydrocarbon resulting in the formation of a carbonaceous residue. cartridge seal - A completely self-contained unit, including seal faces, flexible elements, gland, sleeve, etc., which is pre-assembled and pre-set before installation.

cascade seals - Seals which are staged or arranged in series with regulated pressure between adjacent pairs. cavitation - A condition in which vapor or gas bubbles occur locally in liquids, normally in an area where pressure decreases or temperature changes abruptly. The subsequent collapse of the bubbles causes high local impact pressure, which can contribute to equipment wear and reduced seal life. centrifugal separator - A device utilizing centrifugal force to separate impurities or abrasive solids from the seal flush fluid. Generally used with a connection to the pump discharge, allowing an abrasive fluid to pass through the separator, and discharging a relatively clean fluid into the seal chamber and the relatively dirty fluid to waste or to the pump suction. checking - Short radial cracks in the surface of a seal face (see heat checking) or axial cracks on the lip contact surface of elastomeric seals.

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Glossary of Terms - C circulation connection - The inlet and outlet ports of the seal cavity which receive the piping or tubing for circulating liquid in close proximity to the mechanical seal. closing force - The sum of the hydraulic load and the spring load acting on the seal faces to keep them closed. coefficient of friction - Defined in a mechanical seal as the ratio of the friction force at the seal faces to the closing force. coil spring - A type of spring which is formed from wire wrapped in a helix. They may be used singularly or in multiples, with the individual springs oriented about the circumference of a seal assembly. The springs transmit a uniform closing force on the sealing face. coking - The formation of carbonaceous deposits on the atmospheric side of a mechanical seal resulting from oxidation or polymerization of leakage of organic products. composite seal - A seal component or face which is composed of two or more different materials that are usually bonded or molded together. compression set - The difference between the thickness of a gasket or elastomeric seal component before it is compressed and after it is released from compression. Compression set is normally expressed as a percentage of the original dimension and is a function of time, temperature, and fluid effects.

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Glossary of Terms - C concentricity - A measurement made comparing the run out of the seal chamber bore or gland register in reference to the shaft. coning - An axi-symmetric distortion of the faces giving a radial variation in the seal film thickness. contact pressure - The face load, computed as the sum of the hydraulic force and the spring force, divided by the contacting area of the sealing face. containment device – A seal or close clearance bushing which is intended to manage leakage from the inner or outer seal and divert it to a location determined by the user. containment seal – A special version of an outer seal used in Arrangement 2 which normally operates in a vapor (gas buffer or no buffer) but will seal the process fluid for a limited time in the event of an inner seal failure. containment seal chamber – Component or aggregate of components which form the cavity into which the containment seal is installed. coolant - A liquid from an external source circulated through a heat exchanger or some other piece of equipment to remove heat.

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Glossary of Terms - C crystallizing fluid – A fluid which is in the process of forming solids or which may form solids due to dehydration or chemical reaction. cyclone separator - See centrifugal separator.

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Glossary of Terms - D D dead ended - A seal arrangement in which there is no product circulation or injection of flush into the seal chamber for cooling. differential pressure - A difference in pressure between two points in a seal system. Normally the pressure difference across a seal face. dimensional stability - The ability to retain manufactured shape and size after having experienced the combination of operating stresses and temperatures. distributed flush – An arrangement of holes, passages, baffles, etc. designed to promote an even distribution of flush fluid around the circumference of the seal faces. double balancing - A design feature which changes the balance diameter to improve the seals resistance to opening under reverse pressure. This prevents the opening of the inside seal of a dual pressurized (double) seal upon loss of barrier fluid pressure. double seal - Dual pressurized mechanical seal with two seals mounted back-to-back, or face-to-face, designed to maintain a liquid or gas barrier fluid between the seals at a pressure higher than that of the process pressure being sealed.

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drain - A connection for removing liquid from the pump casing, seal chamber, or gland.

Glossary of Terms - D drain - A connection for removing liquid from the pump casing, seal chamber, or gland. drive collar - A part of the seal cartridge that transmits torque to the seal sleeve and prevents axial movement of the seal sleeve relative to the shaft. drive mechanism - A device such as a pin, key, or structural part of the seal designed to transmit torque from the shaft to a rotating seal. Also an anti-rotation device in the seal or bushing. dual mechanical seal - A seal arrangement using two mechanical seals in the same seal chamber in any orientation which can utilize either a pressurized barrier fluid or a non-pressurized buffer fluid. dry-running - Running without liquid present between the sealing surfaces. dual seal - See dual mechanical seal. durometer reading - An index used for measuring the relative hardness of elastomers. dynamic secondary seal - A secondary seal which is designed to slide or move relative to other components to allow for movement of the flexible element.

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Glossary of Terms - E E effective diameter - See balance diameter. elastomer - A natural or synthetic rubber from which seal components such as O-rings, bellows, and gaskets are made.

end face mechanical seal - A device that prevents the leakage of fluids along rotating shafts. Sealing is accomplished by a stationary primary seal face bearing against the face of a rotating mating seal ring mounted to a shaft. The sealing faces are perpendicular to the shaft axis. Axial mechanical force and fluid pressure maintain the contact between wearing seal faces. emissions - A minute release of the sealed fluid to the environment. end plate - See gland plate. end play - Axial movement in either direction, parallel to the center line of a shaft. erosion - Abrasive wear of a surface by small particles in a gas, vapor, or liquid, or droplets of liquid in a gas or vapor flowing across the surface.

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Glossary of Terms - E extended length - See free length. external circulating device – A device located outside of the seal/buffer/barrier chamber to circulate seal chamber fluid through a cooler or barrier/buffer fluid reservoir. externally mounted seal - A seal arrangement that is mounted outside the pump or vessel being sealed. externally pressurized seal - A seal which operates with a pressurized barrier fluid with the pressure applied to the outside diameter of the seal faces. extrusion - Displacement of part of a seal such as an O-ring into a gap under the action of fluid pressure or relative movement. extrusion gap - The clearance on the low-pressure side between components which confine a secondary seal such as an O-ring. extrusion ring - See anti-extrusion ring.

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Glossary of Terms - F F face coating - A dense material applied to the surface of a base material to increase the wear characteristics of the seal face. See hard facing. face - Also called sealing or mating face, either of two lapped surfaces in a mechanical seal, performing the primary seal function. face load - The sum of the spring and hydraulic forces carried at the seal faces. face pressure - See contact pressure face seal - See end face mechanical seal. face width - Radial width of the primary face ring. face-to-back seal configuration – A dual seal in which one mating ring is mounted between the two flexible elements and one flexible element is mounted between the two mating rings and the sealed fluid is on the OD of the inner seal and barrier or buffer fluid is on the ID of both the inner and outer seal.

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Glossary of Terms - F face-to-face seal - Two mechanical seals with rotating components mounted face-to-face with either a common stationary or two stationary rings between the rotating rings and the sealed fluid is on the OD of the inner seal and barrier or buffer fluid is on the ID of both the inner and outer seal. A liquid or gas barrier fluid is used between the two seals which can be either at a higher or lower pressure than the product pressure. (need to resolve references to seal rings) FFKM – See perfluoroelastomer film thickness - The distance separating the two seal faces that form the primary seal. fixed throttle bushing – A one piece cylindrical device that is fitted to the stationary part of the containment seal chamber and has a radial clearance to a rotating component. It is used to help isolate one region from another and assist in channeling liquid leakage to an exit port. The design is intended to maintain fixed radial clearance over the operating life of the seal.

FKM – See fluoroelastomer. flange - See gland plate. flash - Thin extensions on the elastomeric portion of a seal formed by extrusion of the elastomer at the parting lines in the mold cavity.

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Glossary of Terms - F flashing - A rapid change in fluid state, from liquid to gaseous. In a dynamic seal, this can occur when frictional energy is added to the fluid as the latter passes between the primary sealing faces, or when fluid pressure is reduced below the fluid’s vapor pressure because of a pressure drop across the sealing faces. See popping. flashing fluid – A liquid with an absolute vapor pressure greater than 0.1 MPa (1 bar) (14.7 psi) at the pumping temperature, or a fluid that will readily boil at ambient conditions. flashing fluid service - Any service that requires vapor suppression by cooling or pressurization to prevent flashing of the product being sealed. This category includes all hydrocarbon services where the fluid has a vapor pressure greater than ambient pressure. flatness - A characteristic of a seal face as measured by how much the surface deviates from a perfect plane expressed in helium light bands, wherein one helium light band equals 0.0000116 inch (0.29 microns). flexible graphite - Exfoliated and recompressed graphite material used for static (secondary seal) gaskets in mechanical seal design, from cryogenic to hot service. flexible members - That portion of a seal containing springs or bellows. flexibly mounted - A design technique for installing a resilient seal component so that it may compensate for slight irregularities due to alignment or pressures, thereby extending seal life.

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Glossary of Terms - F floating member or element - The portion of an end face mechanical seal assembly that is flexibly loaded. floating bushing - A restrictive ring allowed to move radially so that large motions of the shaft can be accommodated. A floating ring can have a smaller clearance than the fixed bushing seal. fluid film - A film of liquid or gas separating the seal faces generated by hydrostatic and/or hydrodynamic lubrication. full fluid film lubrication - A condition of lubrication in which the seal faces are completely separated by a liquid or gas film. fluid side - That side of the seal which, in normal use, faces toward the fluid being sealed. fluorocarbon - A general class of compounds containing fluorine and carbon such as PTFE and fluorelastomers. fluorelastomer - A fluorocarbon elastomer commonly used as a secondary seal in high temperature and/or corrosive service. Material is a saturated polymer in which hydrogen atoms have been replaced with fluorine (also referred to as FKM). flush - A fluid which is introduced into the seal chamber on the process fluid side in close proximity to the seal faces and typically used for cooling and lubricating the seal faces.

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Glossary of Terms - F flush connection - A tap in the seal chamber or gland plate to allow circulation of the product being sealed, the injection of a clean external flush, or the recirculation of sealing fluid. flush plan – A configuration of pipe, instruments, and controls designed to control the environment around the seal faces (also referred to as piping plan)

free length - The uncompressed axial length of a face seal assembly. The term is also applicable to the free extended length of a spring or a bellows. fretting - A combination of corrosion and wear that occurs due to the rubbing motion of a secondary seal as it removes the protective oxide coating from a metallic shaft or sleeve.

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Glossary of Terms - G G gasket - A device made of several deformable materials used between two surfaces to prevent leakage.

Usually the two surfaces are not in relative motion. gland plate - A pressure retaining end plate which connects the stationary assembly of a mechanical seal to the seal chamber. Also call a gland, end plate, or flange

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Glossary of Terms - H H hang-up - Failure of components to move axially along the shaft under the applied mechanical and hydraulic forces to compensate for seal face wear. hard face - A term for seal face materials of high hardness; e. g., silicon carbide, tungsten carbide, or ceramic.

heat checking - The formation of fine radial cracks on the hard seal face caused by thermal stresses set up by alternate dry running and quenching by cool liquid as a film is reestablished heat load - The sum of seal generated heat and heat soak. heat soak - The energy (btu) convected and conducted from the process fluid into the seal chamber. housing - A rigid structure which supports and locates the seal assembly with respect to the shaft and forms the seal chamber. housing bore - The cylindrical surface inside the seal chamber. hydraulic diameter - For a bellows seal, the effective balance diameter or equivalent piston diameter at a specific level of pressurization and bellows compression. See balance diameter.

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Glossary of Terms - H hydraulic balance - The axial load resulting only from fluid pressure forces. hydrodynamic lubrication - Fluid film lubrication in which the pressure in the fluid film is generated by relative velocity of the seal faces. This can be either in a circumferential or axial direction. hydrodynamic seal - A seal which has special geometric features on one of the mating faces. These features are designed to produce interfacial lift, which arises solely from the relative motion between the stationary and rotating portions of the seal.

hydropads - Grooves, scallops, slots, etc., cut into the seal faces to enhance face lubrication and reduce heat build up due to friction, by creating a hydrodynamic opening force between the seal faces. hydrostatic instability - Seal face separation occurring when hydraulic opening forces exceed the closing forces. hydrostatic lubrication - Fluid film lubrication in which the pressure in the fluid film is generated external to the seal faces. hydrostatic opening force - The resulting force on the seal faces resulting from the hydrostatic pressure between the seal faces.

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Glossary of Terms - H hydrostatic seal - A seal that incorporates features which maintain an interfacial film thickness by means of pressure. The pressure is provided either by an external source or by the pressure profile of a face seal. hydrostatic step - A circumferential step which is cut in the nose section of a face seal. Its purpose is to generate stiffness characteristics of the fluid film in the interface.

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Glossary of Terms - I I icing - The buildup of ice on the atmospheric side of a seal caused by the solidification of atmospheric water vapor through evaporative cooling of leakage of the liquid being sealed above its atmospheric boiling point. inner seal - Used in Arrangement 2 and Arrangement 3. The seal closest to the pump impeller or process fluid (also referred to as inboard seal). inside-mounted seal - A mechanical seal with its seal face mounted inside the seal chamber which holds the fluid to be sealed. interface - The space between two seal faces. internal circulating device – A device located in the seal/buffer/barrier chamber to circulate fluid through a cooler or barrier/buffer fluid reservoir. internal seal - See inside-mounted seal.

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Glossary of Terms - I internally mounted seal - An arrangement where the mechanical seal is mounted inside the pump or vessel being sealed. In this arrangement the fluid being sealed is in contact with the outer diameter of the seal faces for cooling and lubrication. internally pressurized seal - The sealing components of a seal which are activated by pressure from the inside diameter of the seal face.

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Glossary of Terms - L L lantern ring connection - A tap in the stuffing box housing used to introduce a clean flush between rings of compression packing. Sometimes used to introduce a clean liquid flush into a stuffing box converted into a seal chamber when a flush directly over the seal faces through the seal gland is not possible. lapping - A finishing operation used to produce an extremely smooth and flat surface on a mechanical seal face by the use of small free-floating abrasives in a fluid on a flat surface or diamond charged plates. See flatness. lapped - An extremely smooth and flat condition on a mechanical seal face. leakage rate - The volume or mass of fluid passing through a seal over a given length of time. light band - Refers to the wave length of a helium light band used in the measurement of seal face flatness. liquid film - A microscopic thin layer of lubricate between seal faces.

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Glossary of Terms - M M magnetic seal - A seal that uses magnetic material, instead of springs or a bellows, to provide the closing force. mating face - The lapped face or faces of a mating seal ring. mating ring - A disk or ring-shaped member, mounted on either a shaft or in a housing, having a mating seal face or faces. metal fatigue - A fracture caused by repeated bending and flexing of a metal part. mechanical seal – See end face mechanical seal. mechanical end-face seal – See end face mechanical seal. mechanical load - The load applied to a seal to ensure contact between the wear surfaces, usually accomplished with springs or bellows, as opposed to fluid or hydraulic pressure. minimum compressed length - The length of a spring, bellows, or face-seal assembly which has been loaded to its solid height.

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Glossary of Terms - M mixed lubrication - Condition of lubrication where the seal load between the faces is partly carried by boundary lubrication and partly by fluid film lubrication. multiple seals - A sealing arrangement using more than one seal in the same seal chamber such as dual or triple seals.

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Glossary of Terms - N N nesting - A metal bellows design wherein the shape of the diaphragms is such that they can nest when the bellows is not distended. non-contacting seal – A seal design in which the seal faces are designed to intentionally create aerodynamic or hydrodynamic separating forces to sustain a specific separation gap between the seal ring and the mating ring. non-flashing fluid - A liquid whose vapor pressure at any specified operating temperature is less than an absolute pressure of 0.1 MPa (1 bar) (14.7 psi), or a fluid that will not readily boil at ambient conditions. non-pusher type seal - An elastomeric or metal bellows mechanical seal in which part of the secondary seal is fixed to and does not have to move along the shaft to compensate for seal face wear.

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Glossary of Terms - O O offset - The radial distance between the axis of the seal bore and the axis of shaft rotation. oil resistance - The measure of an elastomer’s ability to withstand the deteriorating effect of oil upon its mechanical properties.

operating length - The axial distance from the seal face to a reference plane of an installed seal assembly. The term is also applied to the dimensional range within which a bellows can safely be operated. opposed seals - See face-to-face seals. optical flat - A transparent disk, usually of fused quartz, which has been lapped flat and polished to within approximately 0.1 light band flatness on one face, or on both faces. It is used to measure flatness of a lapped surface in conjunction with a monochromatic light source.

O-ring - An elastomeric seal ring with an O-shaped (circular) cross-section, which may be used as either a static or dynamic secondary seal.

O-ring groove - The space in which an O-ring is inserted for sealing.

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Glossary of Terms - O outer seal - The seal located farthest from the pump impeller or process fluid. over-balanced seal - A face seal design where the net hydraulic, or closing, force on the face is positive; i.e., the applied pressure tends to close the seal. This is accomplished by the design balance diameter of the seal. ozone resistance - The ability of a material to withstand the deteriorating effects of ozone (surface cracking).

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Glossary of Terms - P P perfluoroelastomer - A fully fluorinated fluorocarbon elastomer commonly used as a secondary seal in high temperature and /or corrosive service exceeding the capabilities of FKM (also referred to as FFKM).

PFE - Perfluoroelastomer; a high temperature, corrosion resistant elastomeric material for static and secondary seals. pitting - Surface voids usually caused by mechanical erosion, chemical corrosion, or cavitation. polymerizing fluid – A fluid which is in the process of changing or is capable of changing, from one chemical composition to another with longer-chain components and different properties, usually becoming significantly more viscous and/or tacky. popping - Intermittent leakage of vapor characterized by a popping sound. See flashing. product - Process fluid being sealed. product recirculation - Circulation of product through the seal chamber to provide cooling. product temperature margin - The difference between the vaporization temperature of the fluid at the seal chamber pressure and the actual temperature of the fluid.

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product vapor temperature margin – (See product temperature margin)

Glossary of Terms - P product vapor temperature margin – (See product temperature margin) porosity - Connected minute cavities in the seal material through which fluids or gases may pass. positive drive - See anti-rotation device and drive mechanism. pressure balance - See hydraulic balance. pressure casing – Composite of all the stationary pressure-containing parts of the seal, including the seal chamber and seal gland plate and excluding the seal ring, mating ring, bellows, sleeves, miscellaneous internal seal parts, and atmospheric side gland connections which cannot be isolated from atmospheric pressure. pressurized seal - A term which is applied to a dual (double) seal installation with pressure between the two seals. primary ring - A ring shaped component that forms the primary sealing face with the mating ring. It is flexibly mounted and has axial freedom.

primary seal - The flat mating seal faces which are perpendicular to the shaft in a mechanical seal. primary seal carrier - That component of a face seal assembly into which the non-rotating primary sealing ring is assembled by a shrink fit or by other mechanical means.

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Glossary of Terms - P process fluid - Either a liquid or gas to be contained by a seal.

PTFE - Polytetrafluoroethylene, a semi-rigid fluoropolymer with excellent thermal and chemical resistance and a low coefficient of friction. PTFE may be compounded with fillers (such as molybdenum disulfide, graphite, pigments, and glass fibers) or otherwise modified to improve wear characteristics and other properties.

pumping ring - A device within a seal chamber that circulates fluid in the axial or radial direction through a closed loop for cooling purposes.

Pusher seal - A seal in which the secondary seal is mounted between the seal ring and the flexible element and the sleeve or seal gland plate in which this secondary seal accommodates axial movement to compensate for wear and misalignment.

PV value - The product of face pressure and relative sliding velocity. PV is used to provide a measure of the severity of the service and may be related to seal life. Few seals wear out.

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Glossary of Terms - Q Q quench - A neutral fluid, usually water, steam, or nitrogen introduced on the atmospheric side of the seal to retard formation of solids that may interfere with seal movement. May be used to prevent coking, crystallization, or icing. quench chamber - An enclosed space on the atmospheric side of a seal to which a quench is introduced.

Normally fitted with an auxiliary seal or bushing to prevent excessive leakage to atmosphere.

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Glossary of Terms - R R radial play - Movement perpendicular to the shaft. recirculation flow - The flow of product from the pump discharge through the seal chamber and back to the pump impeller, or the back of the pump impeller through the seal chamber to suction. Also known as a bypass seal flush. reverse balancing - Selection of seal balance so a mechanical seal can withstand pressure on the inside diameter of its face rather than the outside diameter. reverse circulation - Flow of product from the pump impeller through the seal chamber and to pump suction to provide cooling for the seal and to reduce solids at the seal faces. resiliency - The property of a sealing material that provides the ability to maintain constant sealing pressure, despite wear, misalignment, or out-ofround conditions. reservoir - A container or tank used to hold a barrier or buffer fluid for a dual seal system. retainer - Component of the seal head that holds the primary ring, springs, secondary seal, etc., into one unit.

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Glossary of Terms - R rotating seal ring - The rotating primary ring or mating ring mounted on the shaft or other rotating part of the equipment. rotor - That portion of an end face mechanical seal that rotates with the shaft. run-in - The period of initial operation during which the seal face wear rate is greatest and the contact surface is developed. run-out - Twice the distance which the center of a shaft is displaced from the axis of rotation; i. e., twice the eccentricity. Also known as Full Indicator Movement (FIM). running torque - The torque required to sustain a shaft in rotary motion when operation is under stabilized conditions.

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Glossary of Terms - S S seal assembly - A group of unitized detail parts which includes sealing surfaces, provisions for initial loading, and secondary sealing mechanisms which accommodate the radial and axial movement necessary for installation and operation of a mechanical seal. seal balance – See balance ratio. seal cage – See lantern ring. seal cavity - See seal chamber. seal cavity pressure - The pressure acting on the seal assembly. seal chamber - The component, either integral with or separate from the pump case (housing), that forms the region between the shaft and casing into which the seal is installed. seal environment - The physical and chemical conditions in the seal chamber. seal face - The lapped surface of the seal ring that comes in close proximity to the other seal ring face forming the primary seal.

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Glossary of Terms - S seal face width - The radial dimension of the sealing face measured from the inside edge to the outside edge. seal housing - A structure which supports and locates the primary seal and forms the seal chamber. seal ring – disk or ring shaped member that has a seal face on a radially extending surface. seal size - The maximum diameter of shaft or sleeve that will pass through a seal. seat - See mating ring. secondary containment - An arrangement with a chamber on the atmospheric side of a mechanical seal to contain leakage in the event of seal failure. secondary seal - A device (such as an O-ring, flexible graphite ring, flexible graphite filled spiral wound gasket, or bellows) that prevents leakage of the sealed fluid barrier fluid, buffer fluid, or quench medium through parts other than the inner or outer seal faces, the containment device or designated drain. segmented floating carbon throttle bushing – A floating carbon throttle bushing which is composed of circumferential segments retained by a tensioning device. The design enables the clearance around the sleeve or shaft to be significantly smaller than a solid ring floating carbon throttle bushing.

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Glossary of Terms - S shaft eccentricity - The radial distance which the geometric center of the shaft is displaced from the axis of shaft rotation. shaft out-of-round - The deviation of the shaft from a true circle. shaft roughness - Those irregularities on the surface of a shaft, usually measured as roughness average, Ra. shaft run out - Dynamic run out, twice the distance which the center of a shaft is displaced from the axis of rotation, i.e. twice the eccentricity. shaft sleeve - A cylindrical component placed over the shaft to protect it from wear and corrosion. Shore hardness - The relative hardness of an elastomer measured by a Shore durometer instrument. single seal - A seal arrangement with only one mechanical seal per seal chamber. slinger - A washer-like device mounted on the rotary shaft between the seal gland and bearing housing. Used to impart radial momentum (sling) to a liquid in order to keep liquid away from the seal or bearing. solid length - See minimum compressed length. spiral-wound gasket - A static sealing device which is formed by winding a metal and a suitable filler layer into a spiral.

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Glossary of Terms - S split seal - A seal which has its primary sealing elements and other components split in a plane parallel to the axis of the shaft. The result is that the rings are each essentially two semicircles. spring force - The axial force exerted by a spring to overcome dynamic force and any secondary seal friction. spring free length - The total unconfined length of a spring. For a garter spring, it would not include the nib length. starting torque - The torque which is required for initiating rotary motion. static secondary seal – a secondary seal between two surfaces that have no relative motion.

stationary seal ring - The non-rotating primary ring or mating ring mounted on the gland plate or other motionless structural part of the equipment. stick-slip - A friction phenomenon which can be described as a start-stop motion which sometimes results when one surface is being dragged across another. Normally it is associated with a non- lubricated or boundary- lubricated condition.

STLE - Society of Tribology and Lubrication Engineers. stuffing box - A cylindrical cavity and the enclosing stationary parts surrounding a shaft, designed to accept a compression packing for the purpose of restricting leakage along the shaft. May be inadequate when used as a seal chamber.

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Glossary of Terms - S stuffing box pressure - The pressure acting on the product side of compression packing or a mechanical seal. swelling - To increase in volume or become larger, such as an elastomeric O-ring swelling due to chemical attack or elevated temperatures.

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Glossary of Terms - T T tandem seal - A dual non-pressurized seal arrangement with the two rotating components mounted one after the other with faces oriented in the same direction. A liquid or gas buffer fluid is maintained between the two seals at a pressure lower than that of the product fluid being sealed.

TAPPI - The Technical Association of the Pulp and Paper Industry, Atlanta, Ga. throat bushing - A device that forms a restrictive close clearance around the sleeve (or shaft) between the seal or inner seal of a dual seal cartridge and the impeller. throttle bushing - A device that forms a restrictive close clearance around the shaft (or sleeve) at the atmospheric end of a mechanical seal gland. Types include the fixed throttle bushing and segmented floating throttle bushing.

TIR (total indicator reading or total indicated runout) – The difference between the maximum and minimum readings of a dial indicator or similar device when monitoring a face or cylindrical surface during one complete revolution of the monitored surface. torque - The resistance to shaft rotation caused by a seal’s frictional drag.

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Glossary of Terms - T torsional vibration - A vibration which has a circumferential or angular sense. It is often generated by a stickslip action between mating faces. tracking pattern - The path the primary seal makes rubbing against the mating ring, gland plate, or shaft. tribology - The study of rubbing friction applications.

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Glossary of Terms - U U unbalanced seal - A seal in which the faces are subjected to full, or greater than full, hydraulic pressure in the seal chamber. See over balanced seal and under balanced seal.

U-cup - A type of secondary seal with a U-shaped cross section.

under balanced seal - A seal designed so that the balance diameter has a net hydraulic closing force which is negative; i. e., applied fluid pressure tends to open the seal. uni-rotational seal - A seal designed for applications having a single direction of shaft rotation. unitized seal assembly - A cartridge seal. An assembly in which all components necessary for accomplishing the complete sealing function are in a single package.

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Glossary of Terms - V V vapor pressure - The pressure at a given temperature below which a liquid changes to a gas. The vapor pressure of a petroleum product determined by the ASTM Standard D-323 procedure. vent connection - A connection in the gland plate outboard of the seal chamber through which leakage may be vented to a recovery system. vented seal - A term applied to sealing systems in which the pressure between two seals is purposely maintained at a low level in order to prevent mixing of the two upstream fluids in either of the higherpressure-level upstream compartments.

V-ring seal - A seal consisting of a ring or nested rings which are of V-shaped cross section and commonly made from elastomeric or PTFE materials. Spring loading is used to maintain contact between the seal and its mating surface.

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Glossary of Terms - W W waviness - A deviation of the seal faces from circumferential flatness. Waviness can be present on the seal face as manufactured or after running. wear track - See tracking pattern.

wear rate - The amount of seal face surface wearing away over a period of time. wear sleeve - A replaceable cylindrical metal ring generally used in assemblies to eliminate expensive shaft replacement caused by grooving that may occur at the seal-shaft interface. welded metal bellows - A bellows fabricated by welding together a series of thin metal washers on their outside and inside diameters to form an accordion type of structure which, when assembled to other components of a seal assembly, acts both as the secondary seal and as the spring which mechanically loads the assembly. working length - The dimensional range within which a bellows or spring can safely be operated. See operating length.

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