Brent, Your first case compressed is closer to what happens to a properly seated O-ring while as you note in second case, the groove is not deep enough. In the second case, sea pressure can cause the O-ring to extrude into the compartment and you have a bad leak. Parker Hannifin has a great book and software available free to download for the proper design of sealing services. Sikaflex is meant to seal or glue together surfaces that are not meant to be broken regularly. If you were to use Sikaflex, you cannot tell if you have a seal that continuous in nature…there may be air voids and other discontinuities from how you lay down the bead. Additionally most urethanes do not hold up well to exposure to sun light. Sikaflex on the outside of hulls is painted over. Sealed hatches are designed to bottom out with a wide metal to metal surface joint. The trapped O-ring or rectangular ring is designed to be compressed to a certain parameter and trapped. In your design, all of the pressure bearing surfaces are localized to the much smaller area of the welded in circular rods. As Alec stated, after all of the effort spent in welding in these 4 rods and trying to lay down a uniform Sikaflex surface, you would have been much better off (and have an assured safe sealing surface) with spending the $300 to have the surface machined. R/Jay Resepectfully, Jay K. Jeffries Andros Is., Bahamas Save the whales, collect the whole set. From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent Hartwig Hi Alec, I consider that a valid point. My thinking is that if one chooses the right durameter harness of Sekaflex or the like, thickness of urethane under the upper sealing rings, and the right size and spacing of upper sealing rods that the design perhaps could handle the general operating depth of the K-250, K-350 and perhaps higher. 111 psi for the K-250, being pressed mostly down on the hatch, then that load being transferred to the urethane might not damage the harder urethanes. For hatches that go metal to metal under a certain amount of pressure. Once that happens, no more addition pressure from that point is being added to the O-ring to seal it further as I understand it. Of course if the parts are designed properly, you shouldn't have a issue with it staying sealed unless you go much much much deeper then they are designed for. My original hatch has a good size soft O-ring in a square gland on the hatch. It might all fit in the gland and allow the hatch and hatch land to got metal to metal, if you went way to deep, and nothing else on the sub failed. But for some larger cross section O-rings, as well as ones set in a curved gland that gives no place for the O-ring to deform into, in a extreme test, I think it would look like this. Regards, Szybowski
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