<html><head></head><body><p dir="ltr">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.</p>
<p dir="ltr">Sean<br>
</p>
<br><br><div class="gmail_quote">On March 2, 2016 8:32:45 PM MST, Brian Cox via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div style="font-family:Arial, sans-serif; font-size:10pt;"><div>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. </div><div> </div><div>Brian<br /><br />--- personal_submersibles@psubs.org wrote:<br /><br />From: "Sean T. Stevenson via Personal_Submersibles" <personal_submersibles@psubs.org><br />To: Personal Submersibles General Discussion <personal_submersibles@psubs.org><br />Subject: Re: [PSUBS-MAILIST] Hatch interlock<br />Date: Wed, 02 Mar 2016 14:53:19 -0700<br /><br
/></div><p dir="ltr">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.</p></div>
<p dir="ltr">Sean<br />
<br /><br /></p><div>On March 2, 2016 1:19:54 PM MST, Alan James via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote style="margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex; border-left-color: rgb(204, 204, 204); border-left-width: 1px; border-left-style: solid;">
<div style="color: rgb(0, 0, 0); font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);"><div>Sean,</div><div>why not leave the transducer in the 1 atm compartment & just attach it</div><div dir="ltr">to the pipe from the compressor that would run through the wall to the various</div><div dir="ltr">compartments & sealing flanges. There are of course other complications with</div><div dir="ltr">releasing the vacuum pressure on the individual hatches.</div><div dir="ltr">Alan</div><div dir="ltr"><br /></div><div><br /><br /></div><div style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"> <font face="Arial" size="2">
</font></div></div></div></div></div></blockquote></div><hr size="1" /><font face="Arial" size="2"> <b><span style="font-weight: bold;">From:</span></b> Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org><br /> <b><span style="font-weight: bold;">To:</span></b> Personal Submersibles General Discussion <personal_submersibles@psubs.org> <br /> <b><span style="font-weight: bold;">Sent:</span></b> Thursday, March 3, 2016 8:35 AM<br /> <b><span style="font-weight: bold;">Subject:</span></b> Re: [PSUBS-MAILIST] Hatch interlock<br /> </font> <div><br /><div><div><div dir="ltr">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.</div>
<div dir="ltr">Sean<br />
</div>
<br /><br /><div><div>On March 2, 2016 9:32:49 AM MST, Alan James via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote style="margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex; border-left-color: rgb(204, 204, 204); border-left-width: 1px; border-left-style: solid;">
<div style="color: rgb(0, 0, 0); font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);"><div><span>Sean,</span></div><div dir="ltr"><span>that sounds a good idea. Nuytco set the o-ring on the deep worker hatch externally with a vacuum</span></div><div dir="ltr"><span>pump, but with your twin seal idea you could do this from within the sub without decreasing the hull pressure.</span></div><div dir="ltr"><span> If the transducers are just monitoring the vacuum between the o-!
rings
can't the transducer be</span></div><div dir="ltr"><span>m!
ounted
on the 1atm side of the diver lockout hatch & not be exposed to diver lockout pressure?</span></div><div dir="ltr"><span>Alan</span></div><div dir="ltr"><span><br /></span></div><div><br /><br /></div><div style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"> <font face="Arial" size="2"> </font><hr size="1" /><font face="Arial" size="2">
<b><span style="font-weight: bold;">From:</span></b> Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org><br /> <b><span style="font-weight: bold;">To:</span></b> "personal_submersibles@psubs.org" <personal_submersibles@psubs.org> <br /> <b><span style="font-weight: bold;">Sent:</span></b> Thursday, March 3, 2016 1:41 AM<br /> <b><span style="font-weight: bold;">Subject:</span></b> [PSUBS-MAILIST] Hatch interlock<br /> </font> </div> <div><br /><div><div dir="ltr">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.</div>
<div dir="ltr">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.</div>
<div dir="ltr">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.</div>
<div dir="ltr">Sean<br />
</div>
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