[PSUBS-MAILIST] hatch pin

Wed Mar 23 08:39:30 EDT 2016

Sean,The hatch angle was sitting with a slight tilt to ons side, it was not dogged,the weight of the hatch is sufficient to create the initial seal.  If I have the spring in it will also cause the hatch to tilt a bit when it lands due to clearance in the hinge pin.  I assumed the hatch would press itself into a correct position because it is conical.  I need to do a bit more testing.  Also the o-ring I ordered came to large so I am using  a very old Gamma o-ring that is a bit hard from age.  The vacuum test may not have pulled it all the way down because the o-ring is harder than normal.Hank 

    On Tuesday, March 22, 2016 9:24 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 What is off? O-ring groove / seat parallelism (hatch angle)? Or radial position (concentricity)? Are you dogging it first? Dogging is intended to create the initial recommended O-ring squeeze to create an effective seal at low pressure differentials, before increased external pressure takes over at depth and squeezes them down to the maximum design squeeze when you have metal-to-metal contact at the face seal, loosening your dogs in the process. With a hinged hatch, the part of the O-ring that is radially closest to the hinge will make contact first, and begin to squeeze and support the weight of the hatch from that side first. It is possible that the entire weight of your hatch is fully supported by the force developed by less than the entire o-ring, such that the hinge side is squeezed and the far side is only just making contact. You can even that out by switching to a softer durometer ring, or simply dog the hatch to ensure the minim! umnecessary squeeze on the far side of the ring. You can test if it lines up under increased pressure by piling a bunch of weight on it.You want the hatch to go metal-to-metal as soon as possible, as this eliminates any possible extrusion path for the O-ring (face seals are zero clearance). A softer ring will make this easier, but is also more prone to extrusion before the gap can be closed.  What is your design squeeze at fully closed?Sean

On March 22, 2016 11:15:56 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
Oops, I cut off my e mail.  The amount it is off is maybe  2 thousandths.Hank 

    On Tuesday, March 22, 2016 11:13 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Sean yes it is conical, but when I close it with the o-ring, it does not close tight metal to metal and with the play in the hinge I feel like it is not closing evenly when I do the vacuum test.  I am probably worrying about nothing, likely the hatch is not completely seated metal to metal under vacuum.  I am talking 

 On Tuesday, March 22, 2016 10:18 AM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 What type of misalignment exists? Aren't you using a conical bearing face on your h! atch?That should be self-centering.Sean

On March 22, 2016 9:03:59 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
Hi All,When I built my hatch system, I built it so the hinge pin has moment in it so the o-ring would have full contact before the hatch was fully closed metal to metal.When I vacuum test it, the hatch is not perfectly even in the seat, or at least it seems like it.  I am wondering if I should close the hatch with the o-ring out and the hatch perfectly positioned and then weld bushings to the hinge so the pin has no movement.   Or should I leave it alone and expect that the external pressure will push the hatch into place?  Hank
Scott, did you notice if your hatch hinge has play?
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