Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Patent
1995-06-12
1997-07-08
DePumpo, Daniel G.
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
277180, 277227, F16J 1500
Patent
active
056452845
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
This invention relates to gaskets for sealing joints between parts containing fluid, such as between flanges of pipes and the like, and in particular to such sealing where the chemical and/or physical properties of the fluid presents a particular danger should leakage occur from the joint.
An example of such a sealing problem is between flanges of pipes or the like containing a flow of hydrofluoric acid (HF) at elevated temperature and pressure.
Because of the aggressive nature of the acid, both as a corrosive chemical, a turbulent fluid and an electrolyte, existing gaskets may be susceptible to attack by the acid and thus not considered to be completely satisfactory in providing flange joints with both the degree of sealing and security over a period of time considered desirable for safe operation.
Such a situation of security with respect to containing difficult chemicals under unfavourable physical conditions is not confined to this medium alone and the situation has parallels elsewhere.
It is known from patent specification GB-A-2066383 to provide a spiral gasket arrangement including, in addition to a spiral wound element, radially outward and radially inward solid supporting rings, the former being intended to act as a compression stop for the flanges and the latter being enclosed within a coating of elastomer material, particularly neoprene rubber, to provide a resilient seal between facing flanges to prevent liquid contained in the pipes from passing between the flanges and supporting ring to the spiral wound gasket element.
SUMMARY OF THE INVENTION
Such a gasket arrangement is appropriate for a wide variety of service liquids and operating condition but is limited in respect of particularly aggressive liquids and service pressures, as encountered for instance in the aforementioned hydrofluoric acid plant.
Notwithstanding the fundamental requirements that the elastomer material comprising the seal is resistant to the service liquid, the properties of the material itself limit its ability to do other than protect the spiral wound element per se, that is, it is not good at protecting the flanges from the service liquid. To the extent that such flanges are often protected by a coat of material inert to most liquids, such as epoxy resin, that may be brittle, the ability to use an elastomer material having a soft and yielding nature in combination with such separate flange coating is put forward as a positive feature of the elastomer material rather than a mitigation of drawbacks in requirements.
The elastomer material is only soft and yielding and able to seal against liquid passage between the movable flanges if it is not confined or compressed to the stage where it behaves as an incompressible liquid itself. Clearly this is important so that the inner ring does not behave as a compression stop. Therefore to enable the elastomer material to behave as a seal during displacement of the flanges upon clamping and in operation, it requires the ability to displace or extrude elastically and is formed as a series of ridges and valleys such that the ridges provide a sequence of radially limited sealing points separated by regions into which the elastomer material is locally displaced or extruded without effecting sealing.
However, precisely because such ridges are resilient and displaced or extruded laterally into the adjacent valleys, they are vulnerable to high service liquid pressures which subject at least the inner ridges to forces which may permit deformation and leakage, the overall sealing efficacy being provided by the series of ridges each subjected to less lateral displacement force.
The sealing function provided by such elastomer coated inner ring is thus effected at a series of discrete points and not operable to keep the service liquid from contact with the flanges (unless at very low service pressures it is stopped completely by the first ridge) but only the spiral wound element.
Therefore, the form required of, and taken by, such an elastomer material precludes providing a unita
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DePumpo Daniel G.
Flexitallic Limited
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