Double Metal Jacketed

Double Metal jacketed gaskets are  most  commonly  used  in  heat exchanger applications. They are also used in standard flanges where the service is not critical and at temperatures beyond which a soft gasket can be used.  Since most double jacketed gaskets are custom made, there is virtually no limit to the size, shape or configuration in which these gaskets can be made. This particular type of gasket can be used in a myriad of applications. Since the size and shape are not a problem and since most materials can be obtained commercially, this particular gasket style is popular. It must be remembered that  the  primary  seal  against  leakage,  using  a  double  jacketed  gasket,  is  the  metal  inner  lap where  the  gasket  is  thickest  before  being  compressed  and  densest  when  compressed.  This particular section flows, affecting the seal. As a consequence, the entire inner lap must be under compression. Frequently, the outer lap is not under compression and does not aid in the sealing of the gasket. On most heat exchanger applications the outer lap is also under compression, providing a secondary seal. The intermediate part of a double-jacketed gasket does very little to  effect  the  sealing  capability  of  the  gasket.  In  some  cases,  nubbins  are  provided  on  heat exchanger  designs  to  provide  an  intermediate  seal.  This  nubbin  is  normally  1/64”  (0.4  mm)high by 1/8” (3 mm) 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.