Full face mask is a gas?

[Noviz]

Hi guys... the "experiment" went to the pool last night with mixed reviews... after my dive buddies finished laughing (the instructor who certified me looked at it and said "You're gonna die.") But they're used to me....

I should explain the technology a bit... If you Google "gas mask" you'll fine thousands of styles. My two chief concerns in selecting one were 1.) tight seal 2.) squeezing the nose. I didn't feel like tackling the issue of installing nose blocks like the Ocean Reef Neptune. I selected a mask like this. Inside it is a fitted cup that goes over the nose and mouth. This is the only area subject to residual CO2 buildup. The airflow path is as follows:

1. On the front of the mask where the gas mask cannister goes, I attached the second stage reg.
2. The air enters the mask BEHIND the nose/mouth cup and is directed upwards across the eye ports, thus keeping them defogged.
3. There is a one-way flapper valve on each side of the nose/mouth cup... air enters when you inhale.
4. On exhalation, air exits through a second port on the front of the mask, again through the use of a flapper valve.
This whole air path (in fact the whole device) resembles the Neptune mask.

The results of the test.
1. The seal on the face is great... no problem.
2. The inhalation pressure required to breathe does not cause the mask to collapse against the face (although is does expand/contract).
3. The exhaust valve is adaquate to provide effortless exhalation.

BUT! (here comes the problem)...

Because the exhalation process is through a port that is not conected to the second stage reg, there is no backpressure at the reg after the inhalation phase, causing the reg to freeflow into the mask... not my idea of a good time. (It was funny, because the bubbles were leaking out aroung the seal on the face. Back to the old drawing board.

Now, if you would all please refer to picture.....

The exhaust valve is directly underneath the intake port on the front of the mask. This week's project is to duct them together to allow proper function of the regulator.

All in all, a very encouraging result.

PS - Some one asked how I mounted the second stage... I guess I wasn't too clear. I bought one of those octo holders like this CLICK ME and I sliced it in half. I then crazyglue+tie-wrap attached it over the round intake port where the cannister is supposed to go. I can take any second stage, with the mouthpiece attached, and stuff it into the octoholder... great tight strong seal!

Comments? Any insight from the masses?

 

[bcsean]

I think this is fantastic. I'd think it's a bit dangerous for other divers around though. If they saw you they might just spit their regs out of their mouths when they start laughing. Honestly though, full props for a great project.

When you're talking about ducting the exhaust and intake together, I'm wondering why you need a seperate exhaust port at all? As far as I can understand the reg itself just has the mouthpiece sticking into your mask. Why not let the air exhaust out the reg like any other diving situation?

Also, hows the visibility with the lenses angled like they are?

 

[Gary D.]

Try a heavier material for the exhaust flapper or eliminate that port all together by just sealing it off. I think you will find it will work well for you.

Gary D.

 

[james croft]

I do not believe it needs to be positive pressure, but if you have a reg with adjustable second stage you can use it to tune the breathing of the ffm. The mask won't crush as long as you are breathing as the reg will deliver gas at ambient pressure. If you have an oral/nasal mask inside the mask it will minimize CO2. What model mask are you using ?

 

[NorthernShrinkage]

What about a Drysuit exhaust valve opened wright up for exhaust.... Just a thought

 

[Noviz]

Thanks to everyone for suggestions and encouraging words...
Here's where we are in this experiment....
It is necessary to have a flow-through path at the internal oronasal mask in order to prevent CO2 buildup. This makes it impossible to connect the exhaust port from the mask back to the second stage reg. If I did that, the air exhaled would blow back into the intake port and, therefore, into the mask itself. (This would also negate the lens clearing effect of having the dry air from the regulator ducted up the front of the inside of the mask on its way to the internal oronasal mask. (Like that word, "oronasal"? I read it in the DAN magazine!).....

So... the real culprit appears to be the diaphram in my second stage reg... while the inhalation process generates sufficient "pull" to open the airflow, there doesn't seem to be a sufficient drop or reversal of pressure to cause the diaphram to snap back to its closed position quickly. I attribute this to:

1. The inhalation "pull" comes from the oronasal mask, but the air is passed into the internal mask via one way valves. Once the inhalation process ends and the exhalation begins, there is no "push back" to let the diaphrams go...

2. After the inhalation phase is complete, the pressure inside the part of the mask that in NOT inside the oronasal mask is still below ambient pressure, due to it being partially collapsed via vacuum effect during the inhalation. This will make the reg think you are still inhaling, even though you aren't, because the partial prossure inside the mask cavity is lower than ambient.

3. After the reg has sufficiently inflated the mask, the ambient pressure inside the mask will shut off the air flow... but at this point the inhalation process is ready to begin!

So... this is probably why Ocean Reef makes their Nepture mask rigid... other than the pliable vs. rigid issue (and the sheer ugliness of my abomination), they are the same device.

So you regulator technicians... can I adjust this problem away? Or is the flexibility of the mask itself too much "pressure buffer" for a reg to compensate?

Or is my theory just plain wrong? (And how much longer can I withstand the sheer madness and mockery i am forced to endure in the name of science!)

 

[BTK]

I like this. I had a simular idea. I used just the mask. I used some suurgical tubing electrical tape and some hot wax to tap into the mouth piece of my second stage. I ran the surgical tubing into the sides of the mask near the eyes. Took it to the pool and almost choked to death. The seals were bad. Afterall it was just a proto type of one I intend on building. A few things that worked great: The dry air cleared the mask with every breath. Inhale through nose exhale through mouth (just like running). I didn't have that boat paddle of a regular in my mouth (good thing with all the coughing I was doing.) My nose was clear as far as sinuses the dry air seams to open you up. I loved the concept of no mouth piece. It woud be a must for future communication under water. A few things needed a lot of work: There needs to be better seals. The surgical tubing did not have sufficient area for good air flow. If the reg was too low in the water it would free flow. If it was too high it was impossible to breath. The mask needed a purge valve to dump any water. The mask would have worked better if I started with a quality mask that sealed. Walmart snorkel special, a few years old, stored in the bottom of a bucket in the boat. It was a lot of fun playing around with this.

 

[The Horn]

Is there any way to draw and exhale directly via the regulator and bypass the mask cavity? If you passed the regulator through the octopuss cut in half ball thing then reattached the regular mouthpiece you would then breath just through the reg and elliminate the pressure drop causing the free flow?

What about mask flooding? is there any way to clear?

 

[james croft]

That would cause a mask squeeze unless you exhale into the mask to equalize the inside of the mask with outside pressure. Many masks such as the Kirby Morgans and General Aquadynes exhaust from an exhaust T located on the second stage. I believe the trouble exhausting with this mask may very well be that it is flexible and not very rigid. Most band masks also have a one way mushroom valve located below the chin. This allows a method to purge the mask to clear it in the event of flooding.

 

[The Horn]

Yes, but you could always equalize the mask via your nose if there was squeeze