A compression seal fitting, also known as a sealing

gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream ( endocrine gland) or into cavities inside the body or its outer surface ( exocrine gland). Structure ...

, is intended to seal some type of element ( probe,

wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is co ...

conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured free improvisation ...

pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circul ...

tube Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a ...

fiber optic cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with ...

, etc.) when the element must pass through a pressure or environmental boundary. A compression seal fitting may serve several purposes: *It restrains the element from moving as a result of a pressure difference. *It prohibits the leakage of gas or liquid media along the element. *In some cases, it electrically isolates the element from the mounting device. A compression seal fitting, unlike an

epoxy Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional ...

seal Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impr ...

gasket Some seals and gaskets A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. It is a deformable material that is used to c ...

, uses mechanical components and an axial force to compress a soft sealant inside a body which then creates a seal. An epoxy seal differs in that it is composed of some type of compound which is poured into a mold in an attempt to create a seal.

Applications

Typical applications include

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

autoclave An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform steriliza ...

s, holding tanks, pipelines,

furnace A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings * Boiler, used t ...

s, or anywhere wires or sensors need to pass from inside to outside a vessel or wall where the pressure differentials or hazardous environments cause concern.

Components

A very basic compression seal fitting is composed of four mechanical parts: *The body, which holds the elements being sealed and enables the other components to compress into it. *The cap, which secures the sealant and follower into the body. Most importantly, when it is torqued into the body, it pushes the follower into the sealant which creates the axial force and creates the seal. *The follower, which is pushed into the sealant from the torque on the cap and compresses the sealant. The sealant then fills all void spaces around the element and between the body. *The soft sealant (a solid rubber-like component, not a liquid or paste), which surrounds the elements being sealed, and when compressed by axial force creates a

hermetic Hermetic or related forms may refer to: * of or related to the ancient Greek Olympian god Hermes * of or related to Hermes Trismegistus, a legendary Hellenistic figure based on the Greek god Hermes and the Egyptian god Thoth ** , the ancient and m ...

seal. The continuous tension in the torqued body acts like a spring to maintain compression on the sealant and maintain a positive seal. Some soft sealants include

Neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion R ...

, Viton, Teflon (

polytetrafluoroethylene Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Che ...

), Lava sealant ( magnesium aluminum silicate), and Grafoil ( graphite foil). The appropriate sealant for a gland depends on the environment being sealed against. A single compression seal fitting may seal on a single or multiple elements. Sealing glands designed to seal on single elements consist of a body, cap, sealant and follower. When sealing on multiple elements, gland designs also include a seat and an anti-rotation pin to prevent wires or conductors from twisting and shearing. One or more insulators may also be included when electrical isolation is required.

History and development

Soft sealant technology for compression seal fittings was developed in the 1950s by Conax Technologies. Since then, compression seal fittings have evolved to include multiple variations for different applications. Some applications include:

Single-element sealing

Single-element compression seal fittings are used to seal a single element such as a temperature probe, tubewell, pipe, etc. *''Packing Gland (PG) Series'' - for sealing on anything from fragile tubes and soft cables to solid probes or instruments *''Midlock (MK) Series'' - Best used for sealing on metal elements and/or high vibration environments *''Electrode (EG) Series'' - Fully isolating for electrical power or instrument isolation to 8000 V. Teflon insulation and sealant material used for high performance and chemical resistance. *''Split (PGS) Series'' - seals cables and leads when larger probes or connectors are attached.

Multiple-element sealing

Multiple-element compression seal fittings are used when multiple elements of the same or different diameters such as metal tubing, ceramic or rigid plastic tube or pipe, temperature probe, a tubewell, low voltage instrumentation wire, or a power supply feedthrough. *''Transducer (TG) Series'' - For bare wire sealing where elements remain fully electrically isolated throughout the fitting *''Multi-hole Ceramic (MHC) Series'' - Non-isolating fitting for multiple elements up to {{convert, 0.125, in, mm, 3, abbr=on diameter *''Multi-hole Metal (MHM) Series'' - A flexible design for special hole patterns, irregular shapes, and mixtures of element sizes *''Split (PGS/SPG/DSPG) Series'' - For sealing elements that can pass through gland body but not the internal components *''Sensor Wire Seal (BSWS) Series'' - For sealing sensor leads in low-temperature and pressure applications. Ideal for embedded bearing temperature sensors, vibrations sensors, and proximity probes.

External links