In pursuit of understanding the center balance poppet.

[rsingler]

I have a few NOS Air1 decals if you're interested. PM me. But me, I'm afraid to even try to remove the Air1 predive switch! Pinching those plastic locking legs after getting brittle with age has me spooked. I'll fix a Pilot switch before I'll touch an Air1 switch.

 

[EdTeach]

Same here. I don't mess with the switches unless I have to. That being said, they will come off and go back on if you are careful. I have some AIr 1's without the sticker and have never noticed a leak. I have Air 1 / D-Series rebuild kits and poppets, but it would be really nice to know that the D420 poppets are backwards compatible. Is that correct?

 

[rsingler]

...it would be really nice to know that the D420 poppets are backwards compatible. Is that correct?

No. The poppets themselves are not backwards compatible. There are four spokes in the D-400 poppet cap. In the D-420, the spokes have been moved to the inside rim of the housing. In both cases, they help center the poppet. But the poppets are differently shaped.
The remaining question is, since the poppet seats appear to be the same size, can the D420 poppet be disassembled, and the seat used in an old D? For me right now, that's too expensive an experiment to make until poppets are available individually outside the kit.

 

[lexvil]

While I haven’t tried it yet mainly because I don’t want to sacrifice a 420 kit the metal poppet looks like it would fit so does the seat but as Rob has pointed out the seat holder is different

 

[halocline]

I've changed the o-ring in the dive/predive switch on converted pilots and air1s before, it's just a standard o-ring. You can also use a standard o-ring (maybe 116?) on the D series switch, but it's a real pain to get seated. I have found that the standard o-rings tend to last longer than the SP square one.

I have found that the few air1s I've actually dove with breathe pretty wet inverted, enough so I don't use them. The pilot metal case seems to be better in this way, the diaphragm seems to seal better around the edges and lets lees water in on exhalation. It might just be the ones I've used. I've bought several air1s for the diaphragm, which I use on my converted pilots. It's very easy to tear those diaphragms or to find them torn when buying one of the regs.

 

[lexvil]

I've changed the o-ring in the dive/predive switch on converted pilots and air1s before, it's just a standard o-ring. You can also use a standard o-ring (maybe 116?) on the D series switch, but it's a real pain to get seated. I have found that the standard o-rings tend to last longer than the SP square one.

I have found that the few air1s I've actually dove with breathe pretty wet inverted, enough so I don't use them. The pilot metal case seems to be better in this way, the diaphragm seems to seal better around the edges and lets lees water in on exhalation. It might just be the ones I've used. I've bought several air1s for the diaphragm, which I use on my converted pilots. It's very easy to tear those diaphragms or to find them torn when buying one of the regs.

I rarely go inverted at home diving dry but I’ve messed with my 6 A1’s and found inverted goes better if breathing slowly but always need to be prepared for a slug of water. Parts for discontinued regulators are always a challenge, Cannibalization for parts is the end result.