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Jon, Thanks for the clarification, I
stand corrected. I think what I was remembering is described in 7.5.3
Sealing, 4th paragraph. From reading this whole section, it appears
while O-rings have their applications, the major force transmission on port to
hull is on flat surfaces. Review of the diagrams associated with this
passage show that the O-ring forces are either radially (90 deg.) out from the
forces on the port or tangential on the edge. In the slides presented at Holland,
in line force of a port against an O-ring set up high localized stresses that
lead to early port failure. See my attached image for the two cases we
want to avoid. While 2 O-rings lessen the stress concentrations in the
acrylic in the depicted cases, we still want to avoid this. R/Jay Respectfully, Jay K. Jeffries Andros Is., Bahamas Talk sense to a fool and he calls you foolish. - Euripides (484 BC - 406 BC) From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of jonw@psubs.org Jay, I checked Chapter 7.5.3 in Jerry's book and it looks like
he approves two instances of o-ring use for flat plane disc
viewports. One is where the viewport face (external pressure side) is
chamfered 45 degrees and the o-ring sits in the chamfer space sealing against
both the acrylic and thru-hull. The other is is where a groove is cut in
the cylindrical face of the thru-hull. Also, there's an interesting contradiction in the book that perhaps
you could comment on. Chapter 7.5.3 (page 237) Third paragraph, sentence two. vs Fourth paragraph, sentence one. Jon |
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