<html><head></head><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px"><div id="yui_3_16_0_ym19_1_1469125580979_4088"><span>Thanks' Sean,</span></div><div id="yui_3_16_0_ym19_1_1469125580979_4087" dir="ltr"><span id="yui_3_16_0_ym19_1_1469125580979_4189">Okay I get it now, I see why glass does not work. </span></div><div id="yui_3_16_0_ym19_1_1469125580979_4087" dir="ltr"><span>Hank</span></div> <div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 12px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"><font size="2" face="Arial"> On Thursday, July 21, 2016 12:11 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br></font></div> <br><br> <div class="y_msg_container"><div id="yiv7139115480"><div><div dir="ltr">The window is not really supported by the grease. As the applied force increases, the pressure within the lubricant film increases, and as this exceeds the viscous friction within the fluid, it will just extrude out the open end until the window is sufficiently supported by the metal of the window seat, or the reduced clearance increases the viscous friction in the fluid to match the applied forces. When you have bubbles, your fluid is a heterogeneous mixture of air and grease, but it is all at the same pressure, so it offers the same support to the window (if the bubbles are not open to atmosphere at the edges). The acrylic doesn't care whether air or grease is providing the support. The window isn't really floating on the fluids though, except possibly at low external pressures where the viscous friction in the grease is sufficient to hold it in place against extrusion. Under higher pressures, the thin film lubrication layer is only na!
nometres
thick where the window is actually making contact with the peaks of the metal bearing surface, and that contact area increases with increased pressure. Having the grease film just allows the acrylic to deflect radially in response to load, instead of building larger internal stresses near the mating surfaces. You can use such windows without grease at all, but they will have higher friction at the interface, and thus creak more as the higher stresses are built up and relieved when radial forces exceed the coefficient of friction. With gaskets, there is typically no relative movement at the mating surfaces, and it is the gasket that deforms to accommodate the relative movement.</div>
<div dir="ltr">Sean</div>
<br clear="none"><br clear="none"><div class="yiv7139115480yqt7830969552" id="yiv7139115480yqtfd78530"><div class="yiv7139115480gmail_quote">On July 21, 2016 9:51:58 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="yiv7139115480gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex;">
<div style="color:#000;background-color:#fff;font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"><div><span>Sean,</span></div><div dir="ltr" id="yiv7139115480yui_3_16_0_ym19_1_1469115551725_7440"><span>Thank you, you are the man! I probably had to much grease, but that aside, if there are air </span>bubbles, would that not impact the load bearing. The point location of the bubble will not support the port. It is with that logic that I assumed a super fine scratch would not impact the load bearing capacity. Yes I was hoping the grease gods would off set my fine scratches. </div><div dir="ltr" id="yiv7139115480yui_3_16_0_ym19_1_1469115551725_7440">Hank</div> <div class="yiv7139115480qtdSeparateBR"><br clear="none"><br clear="none"></div><div class="yiv7139115480yahoo_quoted" style="display:block;"> <div style="font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"> <div style="font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px;"> <div dir="ltr"><font size="2" face="Arial"> On Thursday, July 21, 2016 9:39 AM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br clear="none"></font></div> <br clear="none"><br clear="none"> <div class="yiv7139115480y_msg_container"><div id="yiv7139115480"><div><div dir="ltr">In general, you want a 64 microinch finish on all window seat bearing surfaces, except for if you are using bearing gaskets in which case 125 microinch surface finish is acceptable where the gaskets are. High vacuum grease, if used, is not intended as a fluid thrust bearing (it is not completely encapsulated by seals), nor as a seal in of itself, but rather to provide thin-film lubrication to enable the acrylic surface to slide against the seat as it deflects under pressure, to prevent localized creep or fretting at the interface surface. As with all thin films, you need add only enough grease to make the surfaces shiny - ex!
cess
grease will be extruded anyway. Air bubbles are really only a cosmetic problem, provided the encapsulating surfaces surrounding the bubble remain lubricated . The seal is generally outboard, so it is just the thrust load squeezing the bubbles, and they will either compress and return, or simply be extruded !
out. You
can try assembling the window into the seat under vacuum to minimize them (no air, no air bubbles), in conjunction with minimizing the amount of grease.</div>
<div dir="ltr">If you have scratches on the bearing surface, the grease only helps insofar as it allows the window surface to slide over the scratch as it moves. A deep / wide scratch may allow the acrylic to creep and locally deform at that location, allowing it to get hung up as the rest of the window moves. This will probably manifest itself as a particularly creaky window.</div>
<div dir="ltr">Use Dow-Corning High Vacuum Grease, applied under clean conditions to cleaned surfaces using a gloved hand or lint-free applicator, and wipe away excess grease before mating the window.</div>
<div dir="ltr">Sean<br clear="none">
</div>
<br clear="none"><br clear="none"><div class="yiv7139115480gmail_quote">On July 20, 2016 10:27:53 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="yiv7139115480gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204, 204, 204);padding-left:1ex;">
<div class="yiv7139115480yqt0115472634" id="yiv7139115480yqt68667"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12px;"><div id="yiv7139115480yui_3_16_0_ym19_1_1469030880979_4063">Hi Sean,</div><div dir="ltr" id="yiv7139115480yui_3_16_0_ym19_1_1469030880979_4063">I have a couple questions. Can I assume that grease trapped in super small scratches in the port seat will carry the load of the acrylic. These are swirls left after sanding and polishing the seat. How much grease do I actually put on the seat? When I grease the seat with a very thin layer, air gets trapped in small bubbles even when I rotate the port. I have seen these marks in the grease in pictures of other subs with conical ports. Are those air bubbles a problem or will they squeeze out under pressure?</div><div dir="ltr" id="yiv7139115480yui_3_16_0_ym19_1_1469030880979_4063">Thanks'
Sean</div><div dir="ltr" id="yiv7139115480yui_3_16_0_ym19_1_1469030880979_4063">Hank</div></div></div><div style="margin-bottom:1em;border-bottom:1px solid #000;"></div><pre class="yiv7139115480k9mail"></pre><hr><br clear="none">Personal_Submersibles mailing list<br clear="none">Personal_Submersibles@psubs.org<br clear="none"><a rel="nofollow" shape="rect" target="_blank" href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></blockquote></div></div></div><br clear="none"><div class="yiv7139115480yqt0115472634" id="yiv7139115480yqt55205">_______________________________________________<br clear="none">Personal_Submersibles mailing list<br clear="none"><a rel="nofollow" shape="rect" ymailto="mailto:Personal_Submersibles@psubs.org" target="_blank" href="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</a><br clear="none"><a rel="nofollow" shape="rect" target="_blank" href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></div><br clear="none"><br clear="none"></div> </div> </div> </div></div><div style="margin-top:2.5em;margin-bottom:1em;border-bottom:1px solid #000;"></div><pre class="yiv7139115480k9mail"></pre><hr><br clear="none">Personal_Submersibles mailing list<br clear="none">Personal_Submersibles@psubs.org<br clear="none"><a rel="nofollow" shape="rect" target="_blank" href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></blockquote></div></div></div></div><br><div class="yqt7830969552" id="yqtfd88847">_______________________________________________<br clear="none">Personal_Submersibles mailing list<br clear="none"><a shape="rect" ymailto="mailto:Personal_Submersibles@psubs.org" href="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</a><br clear="none"><a shape="rect" href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target="_blank">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br clear="none"></div><br><br></div> </div> </div> </div></div></body></html>