RE: [PSUBS-MAILIST] Drop weight mechanism

["Sean T. Stevenson" <cast55@telus.net>]

I concur.  O-rings are very reliable devices, provided you select the correct
ring and groove combination for the application (service pressure, dynamic vs.
static, material compatibility, etc.), that you lubricate them correctly as
appropriate to the application, and that you replace them whenever the o-ring
sealed component is opened, or whenever they degrade, such as with age hardening
in high O2 environments or if exposed to UV radiation.  One other thing to
consider is that an o-ring failure is only a casastrophic problem if the
associated leak is too fast to control - certainly true in the case of a main
hatch o-ring, but failure of smaller penetrations may produce a leak rate that
can be easily accomodated by installed pumping arrangements, and may permit
adequate time to surface and deal with the failure or evacuate as necessary.

Also, unless your hand operated hydraulic ram is permanently installed with only
metal to metal connections throughout the entire piping system, there are
perhaps several o-rings in that system subject to failure, not to mention the
piston seals within the hydraulic cylinder itself.

When you think about pressure hull integrity, every penetration has a shutoff
valve close to the through-hull fitting in the event of a failure in the piping
system somewhere inboard of that.  Guess how those emergency valves are sealed?

-Sean



Quoting Brian Cox <ojaivalleybeefarm@dslextreme.com>:

> I think that by the time that O ring fails your hull will be rusting
> through.   If you are concerned you can always periodically replace the O
> rings every couple of years.   I think you are over reacting to the
> possibility of this type of failure, and you are radially changing your
> design for not a very good reason.  Look at the pressure that hydraulic
> systems have, 3000 to 4000 psi .  Those O rings seem to manage ok.  I've
> heard Carsten on this subject and I think I remember him listing a whole
> bunch of hull penitrations on Euronaut.
> 
> Brian
>   -----Original Message-----
>   From: owner-personal_submersibles@psubs.org
> [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Recon1st@aol.com
>   Sent: Thursday, January 31, 2008 6:52 AM
>   To: personal_submersibles@psubs.org
>   Subject: Re: [PSUBS-MAILIST] Drop weight mechanism
> 
> 
>   In a message dated 1/30/2008 3:47:28 PM Central Standard Time,
> ojaivalleybeefarm@dslextreme.com writes:
>     Are you worried about the O ring failing ?
> 
>     Brian
>   Brian yes in a way. To my way of thinking any hole in the pressure hull is
> a concern for
>   leaking. It just seems to me that a hand operated hydraulic ram is
> sufficient to remove
>   drop weights without relying on an o-ring. Every o-ring will fail, it is
> just a matter of when.
>   I also have planned on testing the drop frequently. This seems to be a
> good practice considering
>   the importance of this working if needed.
> 
>   Dean
> 
> 
> 
> 
> 
> ----------------------------------------------------------------------------
> --
>   Start the year off right. Easy ways to stay in shape in the new year.
> 







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