Compression seal fitting

In mechanical engineering, a compression seal fitting, also known as a sealing gland, is intended to seal some type of element (probe, wire, conductor, pipe, tube, fiber-optic cable, 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 seal or gasket, 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 vessels, autoclaves, holding tanks, pipelines, furnaces, 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 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, Viton, Teflon tape), 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:

See also

• Seal (mechanical)
• Stuffing box

References