Sorry guys, I didn't intend for us to get into a hair-splitting debate about 1mm here or there... You're right Hardie, it doesn't really matter getting right down to precise measurements, I was just trying to prove one way or the other that the larger caps would be beneficial.
For the sake of correcting my post though -
WT & Scythe - I had been using the table from AS 1432
Copper pipe and fittings which for Type B copper pipe (which is what I've got) gives 12.70 x 0.91 for DN 15 (1/2"), 19.05 x 1.02 for DN 20 (3/4") and 25.40 x 1.22 for DN 25 (1") pipes. I completely skipped actually doing the area calculation myself by using AutoCAD - draw the circle by radius or diameter, get it to show the resulting area and presto. The error was from me simply copying the text from one set of calculations in AutoCAD over to the other, and forgetting to change the 93 to 227.
I also grabbed the geometry for the caps from AS 3688
Water supply—Metallic fittings and end connectors. Using the AS data, which is quite precise, is obviously overkill but this is the best source of measurements I had at the time, not having actually purchased the parts for my bubble caps yet. AS 3688 does not list the actual sizes for parts, just their nominal geometry so I had to make a few assumptions on the caps. I should point out that the other reason I'm being a bit anal about the measurements is that I'm hopefully getting my plates CNC cut, so was making my drawings as accurate as possible.
When calculating the total bath volume I used the ID of the gasket (I've now changed that to ID of the glass, I don't know how I ended up using the gasket originally), OD of the bubble caps, the OD of one downcomer pipe and the bath depth to get to my results. Andybear, thanks for the comment - this was one thing that I was thinking might be a problem with the caps being so close together. There's only 3.5mm between the outer caps and the central one, but almost 9mm between outer caps, and 8mm between the outer caps and the glass. Hopefully this will be enough for good bubbling.
103% increase in internal area is still correct by calculations, but now using the glass ID which has a slightly larger area makes the resulting bath volume even more negligible at 0.04% difference between the two methods. So again the larger caps are win-win as far as I can tell.
New drawings - hopefully no errors this time.
20s.JPG
25s.JPG
Thanks again everyone for the input. :handgestures-thumbupleft:
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