Aqualung Micra o-ring #20 size?

[Fibonacci]

Just in the process of rebuilding a couple of AL Micras and one Micra ADJ but getting stumped on the correct size for o-ring #20 Part No 8200-46.
Is bigger than a -014 yet smaller than a -015... and is not a French R series!
Appears in good condition ID 13.3mm x 1.80mm
Any clues gratefully received...

 

[Fibonacci]

Checking using Apple Rubber o-ring calculator, seems a -015 70 DURO would work but when tried it just extrudes out before the air barrel is properly home.
Trying a -014 70 DURO which doesn't extrude but is a very tight fit... doesn't feel correct, and an error message on the calculator for excessive stretch.

O-Ring Gland Calculator - Engineering Tool for Dynamic Applications | Apple Rubber Products

 

[Couv]

I just checked McMaster Carr; the site has no metric seal matching those measurements. I also checked the Marco sizing chart for a Japanese Standard (JIS) seal-still no joy. Probably a -014 will be the best fit.

Measure the o.d. of the air barrel and multiply by .97 That should put you in the ballpark for the i.d. of the seal.

Edit:
....ooops, typing over each other.

BTW that looks like a case seal and only subjected to ambient pressure-so as long as it holds vacuum it should be OK.

 

[Fibonacci]

Thanks Couv
Its always tricky measuring old o-rings, who knows how much they have compressed or stretched... or even if it is the OEM o-ring or a close-enough replacement some time in the past!
The air barrel OD is 17.28mm, o-ring groove diameter is 14.84mm, groove width is 2.05mm
Reg case bore is 17.70mm
A -015 is supposedly the best fit using default % of stretch and compression but it won't fit in practice
Maybe a clue in the AL part number?
For ALL other o-rings in this reg, the last two digits represent the ISO 3601/1806 or AS 568 'dash' size.
For this o-ring the part number is 8200-46 but a -046 is actually ID 107.67 x 1.78mm

 

[Couv]

A -015 is supposedly the best fit using default % of stretch and compression but it won't fit in practice

I practice safe sex; but when it comes to the real thing I throw care to the wind. Agree, a -015 should be the correct size, but if it won't fit try a -014. Steal one from a tank valve if you don't have a loose one available.

 

[Couv]

I'm looking at a manual for a "Mikron" REV date 01/03/07 which has similar air barrel as the one in your diagram. The part number for that o-ring is 121706 and is described as 1.78mm x 14 EPDM 80shA which is a -015

Have you lubed it well and ensured it is a high durometer?

 

[Fibonacci]

Aha!
I tried a well-lubed -015 70 Duro and it extruded like a watermelon pip as the air barrel neared rest position ... will try a harder -015 90 Duro.
This is obviously an issue in the Micras... flagged as 'o-ring bind-up' in the AL manual.

 

[Fibonacci]

Nope even a -015 90 Duro extrudes.
Edit -015 90 will work IF you rotate the air barrel slowly as you push it in... thanks Couv

 

[Scubagaskets]

Catalogue - Premium O-rings Provider for Scuba Diving

 

[The Chairman]

I remember using an 014 for my Micras. Great reg.