@Rusty-What is the purpose of the two interior O-rings? I assume they are a leak barrier in shallow depths where outside pressure is insufficient to compress the single rim O-ring.
Richard,
The face-seal O-ring on the outside only seals the end-cap to the flange. The two radial O-rings inside are needed to seal the flange with the clear acrylic tube. See the attached diagram of the enclosure.
-Rusty
Aaaaahhhh, I seeeee, dumb me.
Hello, I was wondering why 2 O-rings are needed between the flange and the tube, but only 1 is needed between the flange and the end-cap. Thanks!
Hi @Matthew, welcome to the forum 
As I understand it, the tubes have diameter variation that can’t be compensated for in the same way that a flat end-cap can be screwed down onto the flange, and the tubes tend to be opened more frequently than the end-caps get separated from the flanges, which increases wear and the likelihood of something getting on an o-ring and compromising the seal. Less robust tolerances and a higher likelihood of failure both seem like good reasons for having some redundancy in the seal.
That said, I didn’t design the tubes, so I’ve asked internally and will get back to you* if our design engineers have anything else to add
Edit: *My reasoning was confirmed:
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