[PSUBS-MAILIST] Hatch interlock

Thu Mar 3 02:13:35 EST 2016

Cheers Alan!  Yes anything oxygen related I am building a pretty good range
if I do say so myself, and the HP air fittings are coming along too.  The
LED is a good idea for an easy visual indication.

On Thu, Mar 3, 2016 at 5:56 PM, Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> 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 would
> be 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,
> Steve
> On 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 able
> to 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 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 y! ou
> 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 pressur! e 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
>
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