Bolt Spacing Requirements for Flange w/O-Ring seal in VACUUM

[Speckworm]

I'm searching for any information regarding BOLT SPACING on large custom mating flanges (48"-120”) that seal a VACUUM vessel with an O-RING. I cannot find any literature with this combination to determine minimum # of bolts. Appendix 2 and Appendix Y only seem to account for positive pressure. Configuration matches App.Y-5.2 Category 3 with an o-ring groove and no hubs. (Bolted flanged door to a vacuum chamber.) I don't see where B16.5 rates for external pressure and Taylor Forge eq. seems to apply for leakage and/or bending between bolts which I do not believe are the same for vacuum. Is there ANY published guidance for this?

 

[Compositepro]

The minimum number of bolts required is zero. My preference would be to use more for when there is no vacuum.

 

[JR97]

Speckworm,

You need enough bolts to provide sufficient preload to obtain the required compression on the o-ring(s) - usually 20-30%. If it is a vertical joint, the weight of the top assembly may well be sufficient to obtain the compression, meaning Compositepro is correct and no bolts are needed. As far as bolt spacing, I would say it depends on the gravity loading on the joint and flatness of the two mating surfaces.

 

[handleman]

There are standard types of couplings for vacuum service. Look up Nor-Cal, MDC Vacuum, A&N Corp., etc.

-handleman, CSWP (The new, easy test)