Hello Jim,
I think single O-rings work great. When I was a younger kid, I had at times enough aquariums to fill most pets stores. So I had seen and monkeyed with, a good number of external filters and other things that needed a really good seal, have some type of double O-ring configuration. Since most of those system were pretty low pressure systems, the o-rings were pretty soft to seal easily at low pressures. This is one reason I was considering installing double O-rings in a hatch, so that it would easily seal near the surface, and as a bonus give me a back up seal.
I think you make a good point about low pressure sealing, from not enough deformation near the surface. This is why I suspect the double O-rings in the Great Lakes sub might be larger and softer O-rings.
In regards to extrusion of O-rings if there is a large gap in between the hatch and the hatch land you might be right. But in my current opinion I think that the square inches of the surface area of the hatch having hydrostatic pressure applied to it, far out strips the surface area on the high pressure side of the outer O-ring surface that is exposed between the gap. So the deeper you go the more the gap gets tighter, thus sealing even more against extrusion. This is one reason I'm not thinking I want a metal to metal configuration for some subs designs I'm working on. Since at some point on a metal to metal configuration the water will simply go over the seal and not even bother to extrude it, since there is no additional pressure being add to further seal the O-ring once the metal surfaces firmly seat against each other, except for a while the outer part of the O-ring might have additional pressure to push it into the inner wall of the gland, in my current thinking. If you have a metal to metal state, I would think there is no place for a O-ring/seal to extrude to, if it's a reasonable hard O-ring/seal.
!
Than
k you for your two cents and the idea exchange. I very much enjoy the discovery and learning process.
Your resident in a vacuum thinker ;)'
Regards,
Szybowski
From: kocpnt@tds.net
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Deep Flight Challengers Interior
Date: Tue, 2 Sep 2008 05:31:51 -0500
Hi Brent,
You should also consider that part of the effectiveness of
a o-ring based on the deformation caused by (in our closing the hatch) and the
fact that a double seal will cut this deformation in half. As it is most psubs
have some problem sealing well in the first 2-5 feet of descent because of this
situation.
Double seals will exacerbate this problem.
use your own judgement, but I,m going with one. Also if
you cannot crush orings enough and have too much metal to metal clearance you
have a MUCH greater chance of extrusion.
My two cents.
Best Regards,
Jim K
----- Original Message -----
Sent: Tuesday, September 02, 2008 1:42
AM
Subject: RE: [PSUBS-MAILIST] Deep Flight
Challengers Interior
Ian,
You have a good grasp of what is going on with
regards to double O-ring/seals used to seal a metal hatch to a metal hatch
land, in my opinion. I don't think it's all that hard to have another O-ring
gland cut when they already are set up to cut one, and the O-rings for are
applications are pretty affordable, in my opinion. I think replacing both
seals at the same time and on a set schedule would be a good plan. Having a
way to see if the outer seal has failed might be good, but would likely
require a hole in between the seals with a small valve and perhaps add a gage
on it, to check to see what is going on. But I figured that since singe seals
have a great history of working well, that if the outer seal failed and I
didn't have a way to know about it at depth, that the inner one would very
likely function properly for the duration of that! dive, and when you got back
to the surface, you can see the space between the seals is full of water if
you have the seals in the hatch land, and if your paying
attention.
Another issue that has been brought to my attention is the
chance for the space between the seals to be compressed enough to perhaps make
air leak out of it, past one of the seals. This might make a suction force
that might keep the hatch down when you try to open it on the surface. It you
had a valve set up, like I just mentioned you could release it that
way.. I don't think there would be a problem like this for a number of
reasons. One being that there isn't much air there to start with and compress
to any real pressure, that would want to pass the seals. If that was a
problem, I would simply cut another nicely curved large gland between the
seals, so the air that is in between the seals and is being displaced by steel
will move into that gland. The highest pressure I would expect i! n that
configuration would be less then 20 psi and once the hy! drostati c pressure
is removed from the hatch, the pressure while be gone.
There is some
that like the seals to keep the metal surfaces from touching and those that
like the metal to touch. My K-250 hatch has a O-ring that is to large to let
the hatch ring and the hatch lead metal touch under normal diving
pressures. I've worked in commercial, residential, and irrigation
plumbing for several years, and have installed and fixed all sorts of
plumbing. In my opinion it's really hard to get a seal when going just metal
to metal, unless you have one of them mesh into the other like a copper
sleeved connection. I know the R300 goes metal to metal, but I think the
O-ring is doing the fine sealing, since you can have a light scratch or grain
of sand in between the mating metal surfaces and wa la you have a leak, if you
didn't have that O-ring/seal.
Jay, I was not talking about the recent
wet exit dome model we have been talking about recently that has a double
O-rin! g arrangement. I did see the metal ring attached the Challengers
glass dome, and wouldn't expect a deep diving sub to not have a metal to metal
configuration. I was talking about double O-rings/seal hatch sealing
arrangements in general. Whether they use O-rings or Square seals, it is
still a double seal configuration for sealing a hatch. If the metal to metal
surfaces truly sealed the hatch on there own, why have the rubber seals as
well, and two at that? Perhaps it's for low pressure periods near
the surface and/or the sand and scratches type issue.
It looks to me
like that entire hatch land face is the same level on the
Challenger.
The basic double seal hatch arrangement I was talking about
was like this assembly model I made a couple years ago. It could be metal to
metal, or not.
http://www.frappr.com/?a=viewphoto&id=2384531&pid=3954513
Then
there is another example ! of a double O-ring used in the hatch of the Great
Lakes Sub, w! ith larg e O-rings that keep the metal surfaces apart during
normal diving ops.
http://www.frappr.com/?a=viewphoto&id=4001713&pid=7375620
Your
resident pipe dreamer
;)'
Regards,
Szybowski
| Re: [PSUBS-MAILIST] Deep Flight
Challengers Interior |
| From: |
owner-personal_submersibles@psubs.org on behalf of
irox (irox@ix.netcom.com) |
| Sent: |
Mon 9/01/08 7:10 PM |
| Reply-to: |
personal_submersibles@psubs.org |
| To: |
personal_submersibles@psubs.org |
A double O-ring only makes sense if you have a leak
detector between the inner and outer O-ring and are
using it to detect when you need to abort the dive.
Otherwise you are just increasing the number of parts
to replace and the complexity of machining require to
manufacture the parts. If the outer seals fails
before it's replacement schedule it has:
- been designed wrong - and probably the inner seal
has as well. [This should never happen.]
- not been replaced at a schedule inspection and has
rotted/failed - the inner seal was also probably not
replaced either. [This should never happen.]
- has been damaged and did not get noticed during
inspection - and the inner seal is probably also
damaged. This may happen, but it would be noticed
with in the first 30feet of the dive.
After 30feet or so of depth, the external pressure is
so much that it's all metal on metal (as Jay als!
o states)
so the O-rings are no longer in use.
Cheers,
Ian.
From: bottomgun@mindspring.com
To:
personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Deep Flight
Challengers Interior
Date: Mon, 1 Sep 2008 18:43:35 -0400
Brent,
Give
it up please. There is a metal to metal surface for sealing with the O-
or square-rings in between. You don’t want to seal glass or acrylic in a
dynamic seal for deep depths (you don’t want to for glass at shallow depths
either). Your port or dome is mounted in a metal ring. If you look
closely at your image you can discern that.
The
Navy doesn’t have a chamber large enough for that, they certify big stuff out
in the ocean for deep depths.
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 Brent
Hartwig
Sent: Monday, September 01, 2008 6:19 PM
To:
PSUBSorg
Subject: [PSUBS-MAILIST] Deep Flight Challengers
Interior
Greetings
Subbers,
I've been looking for a picture showing the interior of the
full ocean depth, 37,000 fsw designed sub, called the Deep Flight
Challenger. I found a very interesting one. The dome looks to be
severely fractured and held together with duck tape. The dome even looks like
it might be made of glass. Perhaps they tested it in the US Navy's
pressure chamber and it didn't go well.
Also note the double
O-ring grands on the hatch land.... ;)'
I've gotten a fair
amount of flack for wanting to use double O-rings for sealing my hatch against
the hatch land.
http://bp3.blogger.com/_FlxDEKxj5U4/R8IeBNG7yII/AAAAAAAAACw/af_AI6qySU8/s1600-h/DSCN1308.JPG
Your resident day
or night dreamer ;)' It of course depends on
which side of the planet your on..
Regards,
Szybowski
|