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<div dir="ltr" data-setdir="false">No annotations for the groove in either set of plans. Directly measured on K600; interpreted from drawing for K350. The seat is marked #10 and in the materials list it shows 5/8 x 1.5 x 25 inches. That dimension along with the drawing I attached earlier allows calculation of groove diameters. The K600 drawing does not specify an o-ring, but the K350 materials list calls for a 471 o-ring.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">You are correct on the 471 and 472 cross-section diameter at .275. I typed it wrong in earlier message.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Sounds like either one will work. I'm likely to go with the 472 as long as it's not too pricey. It might be cheaper to purchase a kit and just make my own hatch o-ring. I've only found pricing at one supplier which was $48 USD and that seems rather steep to me.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false"><br></div><div><br></div>
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On Wednesday, June 9, 2021, 08:19:45 PM EDT, Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org> wrote:
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<div><div id="ydp86e32124yiv9804101443"><div>That particular drawing does not appear to call out the O-ring groove diameter by annotation. Is that on another drawing? I guess you could scale it off. It also appears to show a half-dovetail groove, with a 10° taper on the ID surface, which would negate the need for stretch to hold the O-ring in as long as the narrowest width of the gland is narrower than the O-ring. Even still, you probably want a bit of installation stretch for reasons given earlier.<br clear="none"><br clear="none">What reference are you using for O-ring dimensions? Per ORD5700, 400 series are 0.275" width. A 0.275" ring in a 0.215" gland depth at zero extrusion gap is 28% squeeze, which is acceptable but at the upper limit of the acceptable range for 400 series face seals. A few percent of installation stretch would reduce the cross-sectional diameter just enough to make the resultant squeeze comfortably within the range.<br clear="none"><br clear="none">Extrusion should not be a problem provided the groove is sufficiently wide that when the flanges come metal-to-metal, you don't end up with an excess amount of gland fill. I might shoot for 75% - 85% maximum. Particularly with a dovetail on the inside per that drawing, which will push the elastomer against the acute angle. Also, with 0% squeeze (where the extrusion gap still exists), you don't want a lot of area subject to the external pressure compared to the hatch area acting axially. As pressure increases, you want the squeeze to win over the tendency to extrude. 0% installation stretch on a 0.275" thick O-ring would start you at 0.060" gap. With 5% installation stretch you would start at 0.053" gap. Not significantly different.<br clear="none"><br clear="none">Sean<br clear="none"><br clear="none"><br clear="none">-------- Original Message --------<br clear="none">On Jun. 9, 2021, 17:18, Jon Wallace via Personal_Submersibles < personal_submersibles@psubs.org> wrote:<blockquote class="ydp86e32124yiv9804101443protonmail_quote"><br clear="none"></blockquote></div><div class="ydp86e32124yiv9804101443yqt0155162856" id="ydp86e32124yiv9804101443yqt68278"><div><div class="ydp86e32124yiv9804101443ydpe0ae7f80yahoo-style-wrap" style="font-family:times new roman, new york, times, serif;font-size:16px;"><div></div>
<div dir="ltr">Sean, thanks for that analysis. See attached image for reference to K350.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">I screwed up some of the K600 numbers based upon the plans which turn out not to be accurate. Specifically, the actual K600 hatch seal configuration I see does not match either the K600 plans nor the K350 plans, so somewhere along the way the details were changed without documentation (which Lloyds didn't catch) or I don't have the final set of K600 drawings.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">K600 groove - 23.5 ID, 24 OD, 23.75 mean diameter</div><div dir="ltr"><br clear="none"></div><div dir="ltr">K350 groove - 23.25 ID, 23.75 OD, 23.5 mean diameter, according to the plans.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">BOTH have a groove width of 1/4 inch as shown in K350 image (including dovetail on ID side) and a depth of .215 inches.</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Cross section diameter of both 2-471 and 2-472 is .271 inches. On the K600 that's a 2.1% stretch which would be within the limits you wrote about, but now I'm wondering if Kittredge used the 2-471 on the K350 to reduce the cross-sectional diameter enough to counter the relatively hefty .271 o-ring inside a .25 x .215 channel. Too big of a diameter would cause extrusion at some point, wouldn't it?</div><div dir="ltr"><br clear="none"></div><div dir="ltr">Jon</div><div dir="ltr"><br clear="none"></div><div dir="ltr"><br clear="none"></div><div dir="ltr"><br clear="none"></div><div><br clear="none"></div>
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On Wednesday, June 9, 2021, 05:25:03 PM EDT, Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org> wrote:
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<div><div id="ydp86e32124yiv9804101443ydp48240b4ayiv3206249022"><div>Per ORD5700, stretch should be limited generally to no more than 5%. A 2-471 O-ring (21.955" ID) on a 23.25" gland is 5.90% stretch. A 2-472 O-ring (22.940" ID) on that same 23.25" gland is only 1.35% stretch.<br clear="none"><br clear="none">Sometimes it is advantageous to specify an O-ring which must be stretched for installation in order to create friction against the gland in order to prevent the O-ring from slipping out of the groove if it isn't retained by other means (e.g. dovetail).<br clear="none"><br clear="none">At 5% stretch however, the cross-sectional diameter of the O-ring is reduced by about 2.5% (and at 5.9% squeeze, almost 4%) so the gland depth may need to be reduced accordingly in order to achieve the design squeeze on the O-ring. Per ORD5700, for face seal glands in sizes 425 through 475, that design squeeze is 21% to 29% with no extrusion gap.<br clear="none"><br clear="none">For face seals subject to external pressure, the gland is usually sized with its inside diameter equal to the mean diameter of the O-ring, with tolerance of +1% of that mean ID, but not more than 0.060". The reason for this is that by ensuring that the O-ring is situated on the correct side of the groove for the anticipated pressure, it won't experience premature failure as a result or being shifted across the groove on every pressurization cycle. For a 2-471, that mean diameter would be 22.230", and for a 2-472, 23.215", which would correspond to 1.25% and 1.20% installation stretch respectively, but these are recommended design minimums.<br clear="none"><br clear="none">My guess is that the 23.25" gland ID just provides enough stretch to keep the O-ring from slipping out, and performance in that embodiment was good enough. Provided the cross-sectional diameter reduction and associated gland depth changes are accommodated, the only downside to greater installation stretch is premature aging of the O-ring. (See ORD5700, 3.6).<br clear="none"><br clear="none">Sean<br clear="none"> <br clear="none"></div></div></div>
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