[PSUBS-MAILIST] Hatch interlock

Wed Mar 2 23:05:54 EST 2016

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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