[PSUBS-MAILIST] Hatch interlock

Thu Mar 3 01:56:31 EST 2016

Wow some good products Steve,I had a look at your Ebay product inventory http://www.ebay.com/sch/tfmengineeringaust/m.html?_nkw=&_armrs=1&_ipg=&_from=I can see you will be a great source of knowledge for tracking down those tricky bits & pieces.    If Sean puts an LED between the pressure sensor & the solenoid valve or between the solenoid valve& it's power source, he will be able to see which set of o-rings is not sealing. And if he was Cliff he wouldbe feeding the information to his PLC & displaying it on his HMI.Cheers Alan

      From: Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, March 3, 2016 7:22 PM
 Subject: Re: [PSUBS-MAILIST] Hatch interlock

Hi Sean,
I really like the idea of vacuum monitoring for hatch leaking - nice one. Also Alan a good idea for a single central transmitter monitoring the whole thing.A couple of thoughts from me:
- as well as the vacuum breaker valves on the actual hatches, you'd need individual manual isolation valves in the 1atm chamber so you determine which was leaking, and in case one leaks.
- You could protect the transducer from over pressure with a relief valve in the 1atm chamber (installed on the 1atm side of isolation valves)
- I'm not sure how likely it really is, but if you got salt water into the vacuum space the water would quickly evaporate, leading the salt residue to accumulate over time
- oil lubricated vacuum pumps, or at least the ones I've used, at only moderate vacuum can create smoke/oil vapour which would be uncomfortable in a sub. Using a diaphragm pump or similar you'd probably achieve a much poorer vacuum but no atmospheric contaminants
- a vacuum switch would probably be cheaper and more likely to survive the over pressure, at the cost of less detailed info, ie. This one is good to 200m 
http://www.suco-tech.com/product.php?p=44&c=12
- actually on reflection, I sell digital gauges for SCUBA gas mixing (shameless plug: http://m.ebay.com/itm/Electronic-Digital-Pressure-Gauge-for-SCUBA-Blending-Nitrox-Trimix-Oxygen-/262307605334?nav=SEARCH ) and they are -1 to 400bar(g) in 0.1 bar increments, which would be ok for both the vacuum and over pressure, so it can't be too hard, and requires an ADC resolution of only 12 bits - if 10 levels of vacuum measurement would be ok?
- I have some very reasonably priced transducer samples coming from the same supplier - if they work out ok I could send you one or at least the specs.
- For a quick and easy way of turning high res analogue signals into useful digital data I can highly recommend this Arduino shield: http://rascalmicro.com/docs-precision-voltage-shield/
Brandon has made a couple of 18-bit versions for me, which are good enough for 0.1% readings from oxygen cells and the like. I've been meaning to order some more.Well that turned into a bit of a ramble, hopefully some is useful.Cheers,
SteveOn 3 Mar 2016 3:52 pm, "Sean T. Stevenson via Personal_Submersibles" <personal_submersibles at psubs.org> wrote:

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 vacuu! m pumpcutting 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 y! ou stillreap 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 pressur! e whenthe 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 thelockout 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

_______________________________________________
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 listPersonal_Submersibles at psubs.orghttp://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/20160303/2d43c82b/attachment-0001.html>