Breathing gas sometimes coming out of my nose in CCR diving. Mask issue or OPV ?

[J-Vo]

The opv in my unit is almost too stiff for me to fire doing a positive check. If the opv is firing the loop is unbreathable.

It was 50 to 75 hours on the loop before I stopped having the "nose leakage" issue.

 

[stuartv]

I think it is because of loop volume issue. Sometimes I will take a deeper breath than usual which leads to ADV firing, increase the loop volume and my OPV was not open enough which leads to gas coming out of my nose

And if you are running an electronic unit with a setpoint controller, then when your ADV fires, the loop volume increases AND the pO2 drops, which causes the solenoid to fire, which increases the loop volume even more.

What OPV do you have that can be "not open enough"? An OPV that you cannot push air out of just by exhaling into a full loop is a serious safety hazard. That is recipe for a lung overexpansion injury.

Your post sounds like you might be diving a Choptima, yes?

 

[trimmatters]

I found myself "snorting" weirdly shortly after having made the jump to CC; particulalry toward the end of a long or tiring dive.

Anyway, after getting all the "check you loop volume" advice and that not sitting right, I came across the below.

The more I research this, the more I believe you are correct -- it seems to be a soft palatal air leak (also called Stress Velopharyngeal Insufficiency). This seems to be an issue with some musicians who play wind instruments. I didn't think to take my mask off when it started...I may try that next time it happens.

An interesting article on it I found if anyone is interested.

You can find it in this thread: Has anyone had a “free flowing” nose on a rebreather?

 

[TuckerIdaho]

The more I research this, the more I believe you are correct -- it seems to be a soft palatal air leak (also called Stress Velopharyngeal Insufficiency). This seems to be an issue with some musicians who play wind instruments. I didn't think to take my mask off when it started...I may try that next time it happens.

There's an article out of Australia that talks about pressure, I didn't get a chance to actually dig into it, but I'm wondering if changing loop volume can have an impact (for the better).

 

[ofg-1]

I have a tube of super glue and a big stapler, I can fix that for you.

 

[trimmatters]

There's an article out of Australia that talks about pressure, I didn't get a chance to actually dig into it, but I'm wondering if changing loop volume can have an impact (for the better).

Tried all sorts with loop volume, zero difference.

But long, cold, tiring dives? Yup. For the first few months frequently.

I’d been almost exclusively cave for many years before going CC, and it was ocean diving what with all those currents, and jetties, and boats, and yuck. Can’t recall it happening in a cave.

But I don’t think it lasted more than … 30 hours of breather time/4 months.

 

[Wibble]

You need minimum loop volume for effective rebreather diving. This is the place where you take a deep breath and the loop just gets tight and the Automatic Diluent Valve doesn’t fire. More gas than that is inefficient and affects your buoyancy.

If the loop OPV is firing, there’s too much gas in your loop. Breathe the excess out of your nose to drop to minimum loop volume. If your ascending you should be dumping loop gas from your nose and injecting more oxygen to keep the PPO2 at setpoint; if an electronic CCR then the solenoid will do this, but you, the rebreather pilot, need to keep the loop volume under control.

If the ADV is firing then you’ve not enough loop volume. Add diluent and manage the PPO2 by adding oxygen.

All of the above is standard rebreather diving technique. You need hours on the unit to build experience in managing loop volume.


Sometimes there is a sort of grunting thing that goes on where you cannot stop breathing out — the soft palate issue mentioned above. In my experience this eventually abates. Think there’s some degree of experience that you gain which resolves this.


In any case, you must control your loop volume for effective rebreather diving.

 

[steinbil]

The more I research this, the more I believe you are correct -- it seems to be a soft palatal air leak (also called Stress Velopharyngeal Insufficiency). This seems to be an issue with some musicians who play wind instruments. I didn't think to take my mask off when it started...I may try that next time it happens.

As I mentioned in the thread you linked I have experienced it as a saxophone player, as a result of fatigue. Usually if I'm out of practice and suddenly play for many hours without building up the stamina. That makes me think it's muscular fatigue and something that can be trained. I don't know if it's feasible to dive the CCR often enough to train these muscles, or if some other practice like blowing into a tube in a water bottle (common exercise for brass players and singers) or actually playing a wind instrument would be required.