Aqualung Micra o-ring #20 size?

[Fibonacci]

For such a tiny reg they breathe very well indeed!

 

[Couv]

For such a tiny reg they breathe very well indeed!

Don't tell me that, I just gave one away. Well, the USD predecessor anyway.

 

[buddhasummer]

For such a tiny reg they breathe very well indeed!

Yes, they do. If parts were more readily available I'd re visit them.

 

[iain/hsm]

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...
View attachment 459523

ID 13.3 x 1.80mm is not a normal or standard in the USA. But first can I ask what type of instrumentation you are using for such precise measurement.

The nearest available size to the above you should consider is the French B Metric and sized at ID 13.29 x 1.78mm

In Europe there must be over a dozen 0-ring sizes between the AS 014 and 015 but the one I listed above is the only size with the same 1.78 mm cross section and would avoid the "pinch" problem using a 015 or the stretch problem with the 014.

When in Europe you have to think like us guys no use thinking we all use American AS sizing and the Parker book LOL , Vive la différence

 

[iain/hsm]

I should add using the EPDM compound is a French thing and only from the French. No one else on the Planet agrees however the CEO decided that the group will go EPDM for nitrox and that is that despite the engineering reservation.
It was more a coup d'état from the big cheese than a tête-à-tête with engineering sense and sensibility. For everyone else use Dupont FKM Viton 75 shore.

 

[inka]

ID 13.3 x 1.80mm is not a normal or standard in the USA. But first can I ask what type of instrumentation you are using for such precise measurement.

The nearest available size to the above you should consider is the French B Metric and sized at ID 13.29 x 1.78mm

In Europe there must be over a dozen 0-ring sizes between the AS 014 and 015 but the one I listed above is the only size with the same 1.78 mm cross section and would avoid the "pinch" problem using a 015 or the stretch problem with the 014.

And don´t forget you might have a 0,1 mm tolerance on that kind of material, so 13,3 x 1.80 = 13,29 x 1,78 without any doubt

 

[Fibonacci]

ID 13.3 x 1.80mm is not a normal or standard in the USA. But first can I ask what type of instrumentation you are using for such precise measurement.

The nearest available size to the above you should consider is the French B Metric and sized at ID 13.29 x 1.78mm

In Europe there must be over a dozen 0-ring sizes between the AS 014 and 015 but the one I listed above is the only size with the same 1.78 mm cross section and would avoid the "pinch" problem using a 015 or the stretch problem with the 014.

When in Europe you have to think like us guys no use thinking we all use American AS sizing and the Parker book LOL , Vive la différence

I was using a Mitutoyo Digital Vernier Caliper (recently checked for calibration) but it is difficult to accurately measure an old o-ring due to stretch or compression in service. That is why I tend to use an o-ring calculator like the Apple Rubber one where I can measure the air tube bore in the reg, the air tube diameter, groove diameter and width then calculate the theoretically correct o-ring size (using industry standard % for stretch and compression).

For the Micra ADJ that was a -015 90 DURO (confirmed by Couv re AL service bulletin on the very similar Mikron)

The Micra ADJ reg concerned showed evidence of Bubba-Tech service attempts so I am not certain the o-ring I measured was in fact an OEM original vs a smaller near-enough replacement some time in the past. There was evidence of salt water aerosol ingress so could well have come in via this path.

In later trials the Micra + (non-ADJ) would ONLY accept a -014 70 DURO (a 90 DURO would not compress) and a -015 70/90 simply extruded. I haven't had a chance to measure the air tube bore or diameter to see if they are the same as the ADJ version but the Micra + design IS different.

It is entirely possible Aqualung specified an obscure French B series Metric o-ring but more likely they used commonly available US sizes if only to reduce costs and part inventory complexity.

Sadly there is evidence of cost-cutting in the otherwise impressive Micra ADJ... for example while Parts #21, 27-28 are machined metal, Part #31 Cap Nut 1008-41 is injection moulded plastic yet has no ribs to support the primary sealing flange to the reg body. This flange tends to wing up under load due to creep, and the soft hex head galls up easily after being removed and replaced just a couple of times.
It very much looks like a part originally designed to be made from metal that has simply been re-manufactured in plastic without the necessary redesign.

Now THERE'S an opportunity for a CNC replacement Cap Nut in 316 stainless or Ti... hmmm...

 

[Fibonacci]

Yes, they do. If parts were more readily available I'd re visit them.

I was amazed to read the cracking effort specifications in the Micra ADJ service manual... 0.6" to 1.0" if setup correctly!

 

[buddhasummer]

I was amazed to read the cracking effort specifications in the Micra ADJ service manual... 0.6" to 1.0" if setup correctly!

View attachment 460290

Wow, that's dropping into D series territory. I wasn't into DIY when I owned the Micra Adj buy do remember that it breathed beautifully.

 

[Fibonacci]

Wow, that's dropping into D series territory. I wasn't into DIY when I owned the Micra Adj buy do remember that it breathed beautifully.

I'd say case geometry, volume and Teflon coated lever arm would have a lot to do with that... despite the tiny diaphragm size!