[PSUBS-MAILIST] Bellows add

[Alan via Personal_Submersibles]

Hank,
there is a flaw with the Bellows Add system that I can see, in that if you
have an air leak that increases the cabin pressure then the Bellows Add
system won't add O2. 
Ultimately you are relying on your O2 sensor & even then O2 sensors
have a large failure rate & a life expectancy.
Rebreathers use 3-5 sensors for redundancy & compare signals.
For a large sub you have a lot more time for any failure to have an effect
than you would in a sub like your 1 person or Cliff's. 
Maybe if you insist on a Bellows Add system, have an extra O2 sensor.
The second stage regulator works the opposite way than what you want
with the water pressure pushing on a thin diaphragm that has a lever the
other side that opens the valve. Maybe if you glued the lever to the inside
of the diaphragm you could open a valve with it. You would only use the 
regulator valve though, as the rest would be useless.
Better still, make a small sealed enclosure with a diaphragm on one face
& attach the second stage lever mechanism to the outside against the diaphragm.
That way you could make a screw in / out fine tuning adjuster as per DW.
Alan


> On 25/05/2020, at 1:50 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Hi All, I am looking for ideas on how to make a automatic O2 feed similar to the DW bellows add.  I want a non electronic system.  I was thinking about a scuba second stage regulator conversion, that senses negative pressure to release O2.  Sean???
> Hank
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