[PSUBS-MAILIST] Hatch interlock

Wed Mar 2 23:42:53 EST 2016

There's no requirement for force. Nothing is trying to pull those hatches open, except possibly for if you had a slight cabin overpressure. In service, they would also be dogged. The idea with the vacuum space is just to be able to assess the integrity of the seal immediately following closure of a hatch, and to continuously monitor and use that measurement in conjunction with a limit switch on dog position as a hatch interlock signal (preventing descent or certain pressurization actions in the absence of a confirmed seal).  I would probably try to implement some sort of mechanical arrangement such that cranking the dogs open automatically vents that space, so you don't have to think about extra actions when trying to get a hatch open in a hurry. As the vessel descends, the increased pressure will increase squeeze on the o-rings until you get metal-to-metal for sure - the intermediate space would have to be slightly recessed or otherwise designed to maintain a path to the vacuum
source channel, and would not constitute part of the metal bearing surface in that case. In any event, the vacuum is not intended to hold a hatch against pressure. All hatches will seal with pressure as per normal practice, which is why the lockout chamber has double hatches top and bottom - in addition to being blown down from atmospheric pressure to lockout depth pressure, the lockout compartment may also serve as a decompression chamber while the vessel surfaces, so at any time the pressure in the lockout compartment could be either higher or lower than the surrounding sea pressure. The double hatches are necessary to ensure that there is always one which seals with pressure.

Sean

On March 2, 2016 8:32:45 PM MST, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Sean,  If you are only vacuuming that 1" or so circle in-between the O
>rings will the vacuum be enough to hold it?   Seems like you'd have
>around 280# pounds with a 10 Hg vacuum.   or you could  have close to a
>total vacuum?   25 Hg  ?  then you could get upwards to 700# +  ,  If
>the O rings squeezed all the way down you might get metal to metal,
>then would you still reap the benefit of that area acting as a force?  
>Seems like there would be very little volume of vacuum. 
>
> 
>
>Brian
>
>--- personal_submersibles at psubs.org wrote:
>
>From: "Sean T. Stevenson via Personal_Submersibles"
><personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org>
>Subject: Re: [PSUBS-MAILIST] Hatch interlock
>Date: Wed, 02 Mar 2016 14:53:19 -0700
>
>I will have one transducer per hatch, so that I can track the interlock
>status and seal integrity per hatch. Each transducer is therefore
>exposed to whatever pressure exists at the flange between orings, which
>in the case of the lockout hatches must necessarily include the
>pressure at full lockout depth, because those flanges are exposed to
>full pressure when the lockout is operated.  This means that in order
>for this conceptual design to work, I must accept a larger range,
>lesser resolution measurement for those hatches, but it occurs to me
>now that in every case, I would need to accommodate the maximum
>anticipated pressure on either side of each hatch, if I expect to be
>able to track progressive seal leakage without damaging a transducer.
>Ergo, only the 1 atm spaces could make use of 0 - 15 psia transducers.
>The rest would have to be 0 - 250 psia or whatever, and I may require
>higher resolution signal conditioning (24 bit?) to eff! ectively
>measure the range below 1 ata.
>
>Sean
>
>
>On March 2, 2016 1:19:54 PM MST, Alan James via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>
>Sean,
>
>why not leave the transducer in the 1 atm compartment & just attach it
>
>to the pipe from the compressor that would run through the wall to the
>various
>
>compartments & sealing flanges. There are of course other complications
>with
>
>releasing the vacuum pressure on the individual hatches.
>
>Alan
>
>
>
>
>_____________________________________________
>From: Sean T. Stevenson via Personal_Submersibles
><personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org> 
>Sent: Thursday, March 3, 2016 8:35 AM
>Subject: Re: [PSUBS-MAILIST] Hatch interlock
>
>
>It is not the personnel transfer hatch that presents the problem, but
>rather the egress hatches in the lockout chamber, as those flanges will
>see the lockout pressure in normal operation.  I can get away with a
>larger range pressure transducer for those hatches, but then I lose
>measurement resolution.
>
>Sean
>
>
>
>On March 2, 2016 9:32:49 AM MST, Alan James via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>
>Sean,
>
>that sounds a good idea. Nuytco set the o-ring on the deep worker hatch
>externally with a vacuum
>
>pump, but with your twin seal idea you could do this from within the
>sub without decreasing the hull pressure.
>
>If the transducers are just monitoring the vacuum between the o-! rings
>can't the transducer be
>
>m! ounted on the 1atm side of the diver lockout hatch & not be exposed
>to diver lockout pressure?
>
>Alan
>
>
>
>
>_____________________________________________
>From: Sean T. Stevenson via Personal_Submersibles
><personal_submersibles at psubs.org>
>To: "personal_submersibles at psubs.org" <personal_submersibles at psubs.org>
>
>Sent: Thursday, March 3, 2016 1:41 AM
>Subject: [PSUBS-MAILIST] Hatch interlock
>
>
>Doing some further design on my lockout submersible project, I came up
>with a novel way to implement hatch interlocks, which doubles as a seal
>condition monitor, ! and a means of establishing a preliminary seal in
>the absence of a pressure differential without relying on the hatch
>dogs to p! rovide the initial o-ring squeeze.
>
>My design entails two o-rings per hatch (vessel has six hatches: cabin
>loading / escape, outer lockout loading / escape, inner lockout loading
>/ escape, inner lockout egress , outer lockout egress, and transfer).
>These o-rings are concentric face seals, each residing within a half
>dovetail groove for positive retention of each o-ring when the hatch is
>opened or manipulated. The grooves are oriented such that the flat face
>of each half dovetail faces the intermediate space between the two
>rings. This intermediate volume is not isolated, but rather connected
>(on the sealing flange side) to a vacuum transducer, and piped through
>appropriate valving to a vacuum pump. When the hatch is closed, this
>intermediate space is pulled to vacuum (as strongly as the pump
>allows), then locked off, and the strength of this vacuum is measured
>by the transducer and continuously monitored. The interlock is clear as
>long as the va! cuum holds, a! nd activates the moment the seal is
>rele! ased, instead of relying on some arbitrary movement of the hatch
>to indicate that it is open.
>
>Apart from the obvious expense, I see a potential problem with exposing
>those vacuum transducers in the lockout hatches to high pressure,
>necessitating either a less sensitive transducer that will withstand
>the pressure, or some means of isolating the transducer when the
>pressure approaches the limit of its range - I'm still working this out
>in my head, but I thought I would share anyway.
>
>Sean
>
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
>_____________________________________________
>
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
>
>_____________________________________________
>
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>_______________________________________________ Personal_Submersibles
>mailing list Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles 
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20160302/32e0b51a/attachment.html>