[PSUBS-MAILIST] conical port seal

Sun Jul 31 00:41:12 EDT 2016

Hi Sean,

For a dome window with conical seat, I see you have mentioned that the O’ring needs .01 compression at rated depth.

Is there an approved calc for this to determine displacement?   Hugh

Kind regards,

Hugh Fulton

Managing Director

Beamlock Systems Ltd

113 North Rd, Clevedon,

Auckland 2582, NZ.

Tel: +64 9 292 9115.  Fax: +64 9 292 8737. 

Mobile: 021 680174

Email:  hc.fulton at gmail.com

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From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Sean T. Stevenson via Personal_Submersibles
Sent: Saturday, 30 July 2016 4:04 a.m.
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] conical port seal

Hank - sorry for the delay but I had to check.  PVHO-1 2012 allows for either the gasket or the o-ring seal between the high pressure face and the retaining ring, but if you opt for the gasket as the face seal, the retainer must precompress the gasket to ensure a minimum of 0.01 in (0.25 mm) compression of the gasket between the retaining ring and the face of the axially displaced window AT DESIGN PRESSURE. No adhesives should be necessary, but you might have to calculate your anticipated axial displacement of the window to ensure that you meet the compression requirement at depth.

Seal ring grooves are specifically prohibited on any window surface, but may be machined into non-bearing seat surfaces. I think a radial o-ring seal to the outer cylindrical surface of a truncated conical frustum is permissible (groove in cylindrical surface of seat), provided that sufficient compression of the o-ring still exists as the window deflects at design pressure.

Gasket compression by the retainer ring must be uniform, differing by no more than 25% between bolt locations and midway between bolt locations.

Gasket hardness is only controlled for bearing gaskets. Your seal gasket can be anything that meets your requirements.

Sean

On July 27, 2016 9:14:43 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Okay, I will not machine a groove in the face, it does seem bad.   I am in Canada, so ice is a reality also.  I think I will keep it simple and stick with the gasket--that is acceptable and common.  I will try to resend the picture and you guys can see what I am talking about.

Brian, I think I read that it is bad to put a groove in the seat, also it would be pretty tricky at this point.  I finally have a real nice seat that I am totally happy with.  I got some pointers from karl Stanley that have worked well.  I was over thinking it as usual. lol

Hank

On Wednesday, July 27, 2016 8:38 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

I would not machine a groove in the conical face of the port. Instead, use the chamfer on the outer face, and squeeze a ring between that, the seat, and the retaining ring.

Sean

On July 27, 2016 7:24:18 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Sean,

Yes I did email it-- it is actually a picture from the Stichiw book, and is considered an acceptable option.  I bet if I read it again I will find the spec for the seal.  Personally I like the idea of an o-ring in the port.  I always though that was bad, but I would sure prefer that.  Today I came across a  section in the Stachiw book showing a test sample port with a o-ring groove.  It said there was no cracking initiated from the groove because it was close to the high pressure face of the port.   Maybe I should chuck her up and machine a grove in it.  What do you think a! bout an o-ring.

Hank

On Wednesday, July 27, 2016 7:07 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Did you email it? I don't see it.

I'd be inclined to stick with the PVHO recommendations (or Stachiw's book) for sealing arrangements. I think there is some discussion of gasket hardness and thickness if using a bearing gasket. I don't recall offhand though. A conical frustum window will probably use an o-ring though.

Sean

On July 27, 2016 6:27:11 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Sean,

Did my picture make it?  

Hank

On Wednesday, July 27, 2016 3:41 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

H! ank - sorry, but a picture is worth a thousand words. Can you post a sketch of your present arrangement?

Sean

On July 27, 2016 3:10:03 PM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Sean,

I am trying decide the simplest way to create my low pressure seal on my conical window.  I has a rubber gasket with silicone originally.   I did that so when the acrylic compresses the silicone will drag the gasket along for the ride.  I don't think it will compress much because it so oversized for the depth.  I am wondering now if a thicker softer gasket is better.  The gasket would be compressed by the retaining ring.  If the acrylic does compress, the gasket can expand to maintain the seal in the event that the sub reaches the surface before the acrylic has expanded.

Do you have a recommendation.

Thank you

Hank

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