<html><head></head><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div><span></span></div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2828">I was thinking that if air temperature was above water temperature,</div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2733" dir="ltr">(as you would get in Canada) then you could potentially get overpressure.</div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2755" dir="ltr">One guy on the internet was saying that his lake temperature was </div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2791" dir="ltr">26C & the air temperature was 10C. In this case the pressure in a</div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2790" dir="ltr">sub could increase by a couple of psi through the higher water temperature, </div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2807" dir="ltr">body & electrical heat. </div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2905" dir="ltr">Alan</div><div class="qtdSeparateBR" id="yui_3_16_0_ym19_1_1470284645175_2789" dir="ltr"><br><br></div><div class="yahoo_quoted" id="yui_3_16_0_ym19_1_1470284645175_2670" style="display: block;"> <div id="yui_3_16_0_ym19_1_1470284645175_2669" style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div id="yui_3_16_0_ym19_1_1470284645175_2668" style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div id="yui_3_16_0_ym19_1_1470284645175_2672" dir="ltr"> <font id="yui_3_16_0_ym19_1_1470284645175_2671" face="Arial" size="2"> <hr size="1" id="yui_3_16_0_ym19_1_1470284645175_2801"> <b><span style="font-weight: bold;">From:</span></b> Alan 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, August 4, 2016 4:04 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: [PSUBS-MAILIST] Overpressure on dome<br> </font> </div> <div class="y_msg_container" id="yui_3_16_0_ym19_1_1470284645175_2667"><br><div id="yiv7001238980"><div id="yui_3_16_0_ym19_1_1470284645175_2666"><div id="yui_3_16_0_ym19_1_1470284645175_2907">Sorry, the air temperature in the bellows probably</div><div id="yui_3_16_0_ym19_1_1470284645175_2906">wouldn't lag that far behind the air temperature in the sub & so</div><div id="yui_3_16_0_ym19_1_1470284645175_2908">wouldn't increase the pressure much.</div><div>Yes there would need to be some major leak.</div><div>However there has been a couple of incidents!</div><div id="yui_3_16_0_ym19_1_1470284645175_2909">Alan</div><div><br clear="none"></div><div id="yui_3_16_0_ym19_1_1470284645175_2665"> <br clear="none"><br clear="none">Sent from my iPad</div><div class="yiv7001238980yqt4150660157" id="yiv7001238980yqt76243"><div id="yui_3_16_0_ym19_1_1470284645175_2910"><br clear="none">On 4/08/2016, at 3:52 pm, Alan via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="nofollow" shape="rect" ymailto="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br clear="none"><br clear="none"></div><blockquote type="cite"><div></div></blockquote></div></div><div id="yui_3_16_0_ym19_1_1470284645175_2912"><div class="yiv7001238980yqt4150660157" id="yiv7001238980yqt85344"><div>Sean,</div><div id="yui_3_16_0_ym19_1_1470284645175_2911">thanks for the maths.</div><div>I was thinking that the scenario could arise where you dive with an internal</div><div>temperature of say 30C & set a bellows add system for the pressure at that</div><div id="yui_3_16_0_ym19_1_1470284645175_2913">temperature. Then as you dived down to cool water the temperature in the</div><div>sub dropped to 15C. The air pressure in the sub would gradually halve but the </div><div>bellows add system would build the pressure up with added O2. If you rose</div><div> to near the surface & cruised around letting the sub warm up, you</div><div>could potentially raise the pressure by quite a bit. Hopefully you would notice</div><div>that the O2 % was high in the first place, but if you didn't & the dome retainers</div><div>weren't substantial, it could contribute to a catastrophic situation.</div><div>Hmmm think I'll put in an overpressure alarm!</div><div>Alan</div><div><br clear="none"></div><div><br clear="none"><br clear="none">Sent from my iPad</div><div id="yui_3_16_0_ym19_1_1470284645175_2914"><br clear="none">On 4/08/2016, at 2:49 pm, Sean T. Stevenson via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="nofollow" shape="rect" ymailto="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br clear="none"><br clear="none"></div><blockquote id="yui_3_16_0_ym19_1_1470284645175_2917" type="cite"><div id="yui_3_16_0_ym19_1_1470284645175_2916"><div dir="ltr">The force acting on the dome from the inside is the internal pressure multiplied by the 222D projected area encapsulated by the innermost seal. For example, if your dome is 24" ID and 26" OD (1" thick), if it seats against a single o-ring at the mid diameter, the area would be A = π(12.5)^2 = 491 in. ^2 . Conversely, if the entire window thickness sits against a bearing gasket, the seal extends to the ID, so A = π(12)^2 = 452 in. ^2 .</div>
<div id="yui_3_16_0_ym19_1_1470284645175_2915" dir="ltr">The internal cabin pressure acts uniformly across the entire window, but the external sea pressure does not. Across a 26" OD window, the pressure at the bottom of the window is about 1 psi greater than at the top, so in the absence of proper retention, it would preferentially pull away at the top in the event of overpressure.</div>
<div dir="ltr">As far as what to expect, that number should be zero. The only way you will encounter overpressure is if something is leaking gas into the cabin, or if there is a dramatic temperature increase.</div>
<div id="yui_3_16_0_ym19_1_1470284645175_2918" dir="ltr">Your dome retainers need only be strong enough to hold the dome against its seal at whatever delta-P activates the OPV, or some margin above that if it is a slow valve. As a thought, I might be inclined to spring load the retainer arrangement, so if you have a full bottle dump or some other (otherwise) catastrophic event increasing cabin pressure, the dome could vent that gas until it dropped below the spring load, and then the OPV or manual equalizing arrangements would deal with the rest. Of course, you should avoid that possibility in design, but I'm just throwing that out there.</div>
<div id="yui_3_16_0_ym19_1_1470284645175_2919" dir="ltr">Sean<br clear="none">
</div>
<br clear="none"><br clear="none"><div class="yiv7001238980gmail_quote" id="yui_3_16_0_ym19_1_1470284645175_2922">On August 3, 2016 8:10:56 PM MDT, Alan James via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="nofollow" shape="rect" ymailto="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<blockquote class="yiv7001238980gmail_quote" id="yui_3_16_0_ym19_1_1470284645175_2921" 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 id="yui_3_16_0_ym19_1_1470284645175_2920" 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 id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2592" dir="ltr"> Hi all,</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2476" dir="ltr">need some group input here.</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2475" dir="ltr">I was looking at a picture of Snoopy's dome that Doug posted on Facebook. (below)</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2486" dir="ltr">The 6 dome retainers that are made of plastic were making me nervous.</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2526" dir="ltr">There have been a couple of cases of domes blowing off. I think George Kitrige</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2511" dir="ltr">was one of them. So I wanted a bit of analysis on this scenario in general.</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2591" dir="ltr">What sort of overpressure can you expect at a max!
imum on
a dive?</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2571" dir="ltr">Doug's overpressure valve operates at .5psi but if you were 3psi overpressure</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2717" dir="ltr">the valve wouldn't operate till you were 5ft from the surface & you would have a short</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2702" dir="ltr">time to get the pressure down. Also wave movement would factor in & fluctuate the pressure quickly at that depth.</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2701" dir="ltr">I think the K250 dome is 24" diameter. I calculated out that there would be 452lb </div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2790" dir="ltr">pressure on the dome retainers for every 1psi overpressure. I based this on the area </div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2791" dir="ltr">of a 24" disc, or should I be basing it on the area of the dome? (Sean)</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2743" dir="ltr">At 3psi that would !
be 226lb
lifting force on each of those 6 plastic retainers!</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2854" dir="ltr">What is a good safety factor here? (Sorry for picking on Snoopy Alec)</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2859" dir="ltr">Cheers Alan</div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2800" dir="ltr"><br clear="none"></div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2769" dir="ltr"><br clear="none"></div><div id="yiv7001238980yui_3_16_0_ym19_1_1470274650042_2698" dir="ltr"><br clear="none"></div></div><div style="margin-top: 2.5em; margin-bottom: 1em; border-bottom-color: rgb(0, 0, 0); border-bottom-width: 1px; border-bottom-style: solid;"></div><pre class="yiv7001238980k9mail"></pre><hr><br clear="none">Personal_Submersibles mailing list<br clear="none"><a href="mailto:Personal_Submersibles@psubs.org" target="_blank" rel="nofollow" shape="rect" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</a><br clear="none"><a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target="_blank" rel="nofollow" shape="rect">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></blockquote></div></div></blockquote><blockquote id="yui_3_16_0_ym19_1_1470284645175_2925" type="cite"><div id="yui_3_16_0_ym19_1_1470284645175_2924"><span id="yui_3_16_0_ym19_1_1470284645175_2923">_______________________________________________</span><br clear="none"><span>Personal_Submersibles mailing list</span><br clear="none"><span><a href="mailto:Personal_Submersibles@psubs.org" target="_blank" rel="nofollow" shape="rect" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</a></span><br clear="none"><span><a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target="_blank" rel="nofollow" shape="rect">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a></span><br clear="none"></div></blockquote></div><blockquote type="cite"><div><span>_______________________________________________</span><br clear="none"><span>Personal_Submersibles mailing list</span><br clear="none"><span><a href="mailto:Personal_Submersibles@psubs.org" target="_blank" rel="nofollow" shape="rect" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</a></span><br clear="none"><span><a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target="_blank" rel="nofollow" shape="rect">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a></span><br clear="none"></div></blockquote></div></div><br><div class="yqt4150660157" id="yqt33563">_______________________________________________<br clear="none">Personal_Submersibles mailing list<br clear="none"><a href="mailto:Personal_Submersibles@psubs.org" shape="rect" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</a><br clear="none"><a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target="_blank" shape="rect">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></div><br><br></div> </div> </div> </div></div></body></html>