Metallic gaskets can come in different styles like; double jacket, single jacket, or solid metal. Soft compressible filler material can be flexible graphite, PTFE, or non-asbestos compressed sheet type. The design of a metal jacketed gasket also may require different shapes and the styles mentioned above can be made to a variety. Lamons jacketed gaskets are normally manufactured with a high temperature filler. The standard filler is normally sufficient for applications up to 900º F. Other soft fillers are available for higher temperatures or special applications. The choice of the metal used for the jacketed part of the gasket would depend upon the corrosive conditions being encountered.
Double-jacketed gaskets are probably the most commonly used style of gaskets in heat exchanger applications. They are available in virtually any material that is commercially available in 26-gauge sheet. They are also extensively used in standard flanges where the service is not critical. Since most double-jacketed gaskets are custom made, there is virtually no limit to size, shape or configuration in which these gaskets can be made.
In some cases nubbins are provided on heat exchanger designs to provide an intermediate seal. This nubbin is normally 1/64" high by 1/8" wide. Experience has indicated, however, that there is little advantage to this particular design. The primary seal is still dependent on the inner lap of the gasket doing the brute work and the secondary seal, when applicable, would be provided by the outer lap.
The double-jacketed corrugated gasket is an improvement on a plain jacketed gasket in that the corrugations on the gasket will provide an additional labyrinth seal. It also provides the advantage of reducing the contact area of the gasket, enhancing its compressive characteristics. A double-jacketed corrugated gasket still relies on the primary seal on the inner lap.
Flat metal gaskets are best suited for applications such as valve bonnets, ammonia fittings, heat exchangers, hydraulic presses, tongue-and-groove joints. They can be used when compressibility is not required to compensate for flange surface finish, warpage or misalignment and where sufficient clamping force is available to seat the particular metal selected. They must be sealed by the flow of the gasket metal into the imperfections on the gasket seating surfaces of the flange. This requires heavy compressive forces. The hardness of gasket metal must be less than the hardness of the flanges to prevent damage to the gasket seating surface of the flange.
At temperatures in excess of the range of 900 F to 1000 F where the standard soft filler is normally not recommended, a double-jacketed corrugated metal gasket with a corrugated metal filler can be beneficial. This construction has the advantages of the double-jacketed corrugated metal gasket and, in addition, since the filler is normally the same material as the gasket itself, the upper temperature limit would be determined by the metal being used. This type of gasket, depending upon metal selected, is designed to be a heat exchanger gasket for high pressure, high temperature applications.
Style 341 is the same general configuration as the Style 340, specifically using a 1/32” thick corrugated metal filler. In addition, 0.015” thick flexible graphite will be applied to both top/bottom.
French type gaskets are available In a one-piece jacketed construction for narrow radial widths not exceeding 1/4" and in two- and three-piece constructions for wider applications. This type of gasket can also be used with the jacket on the external edge of the gasket when the application requires the outer edge of the gasket to be exposed to fluid pressure. The most widely used French type gaskets are fabricated using copper sheath. The double-jacketed construction is preferred over the French or single-jacketed construction, where practical, since it provides a
totally sheathed gasket with none of the soft filler exposed.
The majority of applications for single-jacketed gaskets are normally 1/4" or less in radial width. This type of gasket is widely used in air tool applications and engine applications where space is limited, gasket seating surfaces are narrow and relatively low compressive forces are available for seating the gasket.
In the single-jacketed overlap construction the maximum flange width is approximately 1/4". this type of gasket is used when total enclosure of the soft filler material is required and when the flange width makes it impractical to use a double-jacketed gasket.
The double-jacketed, double-shelled gasket is similar to the double-jacketed gasket except that instead of using a shell and a washer, two shells are used in the fabrication of the gasket. It has the advantage of a double lap at both the I.D. and the O.D. of the gasket, adding greater stability to the gasket. The construction will withstand higher compressive loads. Double-shell gaskets are normally restricted to use in high pressure applications.
This particular type of gasket is normally used with very light flanges on duct work handling hot gases. Its construction consists of two French type shields welded together with a Cerafelt filler material on either side of the metal. Metal thickness is normally 26 gauge, rolled on the I.D. to act as a shield.
Round cross section solid metal gaskets are used on specifically designed flanges grooved or othewise faced to accurately locate the gasket during assembly. These gaskets seal by a line contact which provides an initial high seating stress at low bolt loads. They are fabricated from wire formed to size and welded. The weld is then polished to the exact wire diameter.
The Style 370 includes cementing non-asbestos material strips or fiberglass cord to the corrugated faces – typically in the “valleys” or the use of a gasket compound.
Profiled type gaskets offer the desirable qualities of plain washer types and the added advantage of a reduced contact area provided by the V-shaped surface. It is used when a solid metal gasket is required because of pressure or temperature or because of the highly corrosive effect of the fluid to be contained and also when bolting is not sufficient to seat a flat washer.
It flange conditions require a profile type gasket, but flange protection is required as well, the profile gasket may be supplied with either a single-jacketed or a double-jacketed shield. This will provide protection for the flanges and will minimize damage to the flange faces due to the profile surface.
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