More restrictive inhale when face up with regulator

[Akimbo]

An ADV is a feature on a rebreather that automatic delivers diluent through a valve when lung volume gets too low. On the 4 or 5 rebreathers I'm certified on, the only one that works perfectly is the Optima...

Have you been able to isolate the design characteristics that make an ADV effective or ineffective? This probably isn't the thread but I think it would make an informative post in the Rebreather Forum.

 

[timz]

Regulator orientation is certainly the primary factor. But Jim/Oldschoolto’s comment indicated he never detected any difference (paraphrasing). The physics isn’t in question so there must be other factors preventing this very experienced diver from perceiving the pressure change. Biomechanical variations is the only logical explanation I could come up with.

Okay...

An ADV is a feature on a rebreather that automatic delivers diluent through a valve when lung volume gets too low. On the 4 or 5 rebreathers I'm certified on, the only one that works perfectly is the Optima.

So, what's supposed to happen is.... lung volume gets low, the ADV fires to add gas to the lungs so you can keep breathing.
It's an absolute piece of crap on the rEvo. So most of us disabled it.

Is this because the rebreather doesn't run on compressed air?

So the air you breath from the second stage isn't tuned near to the ambient pressure that causes the reduction of lung volume?

 

[Superlyte27]

Imagine you are breathing from a bag. Or perhaps two bags that are linked together. If there is gas in the bag, you can inhale and move that gas from the bag into your lungs. When you exhale, the gas goes back into the bag. Now, imagine that you try to inhale from an empty bag. Is there anything in that bag to fill your lungs? Nope. The bag is empty. So you got no gas. An ADV is designed so that when you inhale from an empty bag, the valve will fire so that you can breathe. On the rEvo, this Adv is simply a lever connected to a valve. The collapsed bag crushes upon itself, pressing down the lever, adding gas. Seems simple enough, too bad it sucks. Actually, it doesn't suck. LOL

If you ever make it to Florida, look me up. We'll go dive a rebreather.

 

[Akimbo]

... But , I also change breathing " BEFORE " changing workload... Rather than waiting for my body to change breathing rate/volume due to workload...

That's a real problem when gathering opinions from experienced divers. So many adjustments/accommodations are on autopilot that just about anything you put them in the water with is "fine"... not very constructive feedback for a design team. Add to that the human tendency to prefer what they currently use and are used to. We call it the comfortable old shoe syndrome.

However, I have learned the hard way that variations in biomechanics can also be huge -- especially when you throw females into the mix.

 

[timz]

Imagine you are breathing from a bag. Or perhaps two bags that are linked together. If there is gas in the bag, you can inhale and move that gas from the bag into your lungs. When you exhale, the gas goes back into the bag. Now, imagine that you try to inhale from an empty bag. Is there anything in that bag to fill your lungs? Nope. The bag is empty. So you got no gas. An ADV is designed so that when you inhale from an empty bag, the valve will fire so that you can breathe. On the rEvo, this Adv is simply a lever connected to a valve. The collapsed bag crushes upon itself, pressing down the lever, adding gas. Seems simple enough, too bad it sucks. Actually, it doesn't suck. LOL

If you ever make it to Florida, look me up. We'll go dive a rebreather.

Haha... i'm from Malaysia. It's 16 000km away. Though I've been to florida this year for 4 dives.

 

[Akimbo]

... Now, imagine that you try to inhale from an empty bag. Is there anything in that bag to fill your lungs? Nope...

It might be worth mentioning here that the reasons the bag might be empty or low on gas volume is because you go deeper and the gas compresses, part of the volume (Oxygen) is converted to CO2 and absorbed by a chemical, and/or there is a small leak. There is an OPV (Over Pressure Valve) similar to a BC that allows expanding gas to vent on ascent.

 

[timz]

It might be worth mentioning here that the reasons the bag might be empty or low on gas volume is because you go deeper and the gas compresses, part of the volume (Oxygen) is converted to CO2 and absorbed by a chemical, and/or there is a small leak. There is an OPV (Over Pressure Valve) similar to a BC that allows expanding gas to vent on ascent.

I know The reduction in volume due to pressure. I just don't know how ebreather works.

Now i know. It's simply air interchanging between lungs and a container. So, when we suck air from the container, O2 becomes CO2. Breath out the excess CO2 and it's absorbed by chemical. Missing air replaced by O2 injection. Process recycles.

When we go deeper, auxilary air is injected to sustain the volume of the container. When we ascent, over pressure valve releases the access air to the water.

 

[Akimbo]

I know The reduction in volume due to pressure. I just don't know how ebreather works...

Keep in mind that my comment was not directed exclusively to you. Thousands of people of all skill levels read these posts over time and I thought the clarification would be useful context for everyone without exposure to rebreathers of any kind. It is funny how sometimes it can feel like a private conversation on Scubaboard.

 

[timz]

This happens to all other forums of all interest.

 

[eelnoraa]

When your regulator diaphragm is above your chest the water pressure on your chest is higher than is the pressure on the regulator diaphragm. This makes it harder to breathe. Each foot of sea water is about .43 lb of pressure.

This is NOT it, not the reason. The reason is described by Superlyte27: The fact you need to fight the "up" force of air acting on the 2nd stage diaphragm. You basically need to pull it "down" ward to activate the orifice. Same reason you get freeflow when mouth piece is facing up and no water in the 2nd stage.