[PSUBS-MAILIST] Hatch interlock

Wed Mar 2 23:51:13 EST 2016

That's a smart idea. I would also tie that valve actuation mechanically into the actuation mechanism for the hatch dogs, so it remains intuitive and doesn't require a second action.

Sean

On March 2, 2016 9:05:54 PM MST, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Yes, didn't think of the pressure you get when you open the door.You
>would need to have a valve to release the vacuum before being ableto
>open the door, perhaps this valve could be a 3 way valve, letting air
>in between the o-rings& closing the flow to the transducer
>simultaneously. This would stop a low pressure transducer being
>destroyed & stop the vacuum pump cutting in as it would maintain a
>vacuum in the line.Cheers Alan
>From: Brian Cox via Personal_Submersibles
><personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org> 
> Sent: Thursday, March 3, 2016 4:32 PM
> Subject: Re: [PSUBS-MAILIST] Hatch interlock
>   
>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! ectivelymeasure
>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 itto the pipe from the compressor that would run through the
>wall to the variouscompartments & sealing flanges. There are of course
>other complications withreleasing 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 vacuumpump, 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-! ringscan't the transducer bem! ountedon 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 ameans of establishing a preliminary seal in
>the absence of a pressure differential without relying on the hatch
>dogs to p! rovidethe 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! cuumholds, a! ndactivates 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
>
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