Why would a reg become difficult to breathe from?

[MrChen]

There are multiple threads discussing this exact topic. Don’t want to start a tangent on that topic here. You can go look at those threads on questioning whether AI divers use a redundant SPG or not. Some do, some don’t.

Good call

 

[MrChen]

This indicates a local problem inside the affected second stage.
Which means that the secondary reg was operating normally, making it possible to continue the dive.
However, given the situation, I had probably thumbed the dive, too!

Yeah, that's all easy to think about post dive. Two extremely difficult inhales out of the reg, not my reg, strong current, solo, going to 90+ ft... All of that equated to scrubbing the dive. I literally ran that through my head quickly and said nope.

 

[Divin'Papaw]

Actually, it started bubbling in the middle of the first dive. Remember you took GoPro video of it during our safety stop? We were trying to troubleshoot it during the surface interval. I thought it might be a pinched hose o-ring, but then you figured out it was leaking from the transmitter. The issue got worse as we messed with it. I was fortunate enough that it didn't stop working during the dive even though it was blowing bubbles.

Oh yea!!! Thanks for the reminder! I had completely forgotten.

 

[rhwestfall]

@MrChen - you said you were doing a head-first drop and it became difficult. You said fiddling with the knob provided relief. When you did that, were you still in the head down orientation? Or, did you change to horizontal or even head up? I ask as this could be an issue with the tank/dip tube, and adjusting the knob may really have done nothing....

Lots of speculation, and one interesting event you experienced...

 

[Angelo Farina]

Yeah, that's all easy to think about post dive. Two extremely difficult inhales out of the reg, not my reg, strong current, solo, going to 90+ ft... All of that equated to scrubbing the dive. I literally ran that through my head quickly and said nope.

Exactly. Correct decision!

 

[MrChen]

@MrChen - you said you were doing a head-first drop and it became difficult. You said fiddling with the knob provided relief. When you did that, were you still in the head down orientation? Or, did you change to horizontal or even head up? I ask as this could be an issue with the tank/dip tube, and adjusting the knob may really have done nothing....

Lots of speculation, and one interesting event you experienced...

It happened so quickly, it's hard to say what my exact body position was. I was descending down a rope head first. On the first difficult breath, I stopped descending. This did change my orientation, but I can't say how quickly or by how much. In my mind I was head up on the second difficult inhale, but I can't really say. I know that when I turned the valve on the reg and instantly got a good breath, within a second of weighing my options, I began ascending and was in a proper orientation to do so (not head down). With the current, I might have been horizontal holding the rope. My body position wasn't a focus and I moved naturally without having to think about it.

FWIW, the tanks are mine, with new hydro this year. I regularly descend in a head down orientation with my DPV after back rolling off the side of the boat on an almost weekly basis. I used the exact same tank with my regs on the next dive, but it was a drift dive with a giant stride.

Yeah, it was interesting, which got me wanting to ask the question here. If it's my tank, then I want to know that. My hope is to learn something from the event. Unfortunately, I don't know which of my 6 tanks I was using on that dive, and they are all in the shop for fills.

I think my decision making and handling of the situation was good, backed up by the fact that I'm alive to dive another day and can't wait to get back underwater . I don't feel like I was ever in danger since I had adequate backup to an out of air emergency (my pony). Without my pony, knowing how the events worked out, I wouldn't have panicked, but it definitely would have been scary. My redundancy gave me confidence.

Also consider, this is not my reg setup. My personal reg is a rec long hose config with my backup reg around my neck. On this dive, the octo was clipped off to a d-ring, which is not a configuration that I would grab with muscle memory.

 

[lexvil]

let’s revisit the first post;

Last week on a charter, my high pressure SPG hose failed prior to doing the first dive. The crew handed me what looked like a well maintained rental reg set. I believe they were AquaLung regs (could be wrong), and they looked pretty new (no signs of wear or tear). They weren't anything fancy, just a knob to set pre-dive and dive. Dive 1 to 91 feet, zero issues. Dive 2, descending down the rope, at about 40 ft, I suddenly had to really work to get a breath. I did this two times and did get air, but it wasn't sustainable. Think of a large sucking sound to breath. I had the knob on dive and rotated it forward to pre-dive. Just like that, I could breathe again. Since it wasn't my gear and the dive depth was going to be 90 to 100, I opted to end my dive and headed back to the surface. I didn't panic and had a pony bottle. If the reg would have failed or continued breathing hard, I would have just switched to my pony. I've never had my personal regs do this. Could this be caused by the knob not being fully to the dive position, maybe it was bumped slightly from being turned full to dive? I didn't try to turn the knob back to dive once I was able to breath normally.

An additional thought, what if this reg was used by a student and they ran into the same issue? I could totally see them panicking. I did let the crew know why I aborted the dive and reminded them when I handed the reg back to them.

As far as something loose obstructing the air path in the second stage, I would have to assume the the first dive and the first 40 feet of dive two would have cleared anything loose out by then.

fiddling with the “dive-predive” switch is unlikely to have changed anything.

this leaves the tank or the first stage, debris or water in the tank is possible especially if the dip tube is missing but ultimately unlikely to clear itself without changing the orientation from head first which seems likely in this situation, a vis of the tank can prove or disprove this.

it’s been some years since the ACD issue was hashed out but it was full of odd situations that made little sense, not knowing if the loaner reg had an ACD makes this a total guessing game. There are some possible internal issues in a diaphragm reg, although unlikely on a second dive that something sticking and than freeing itself also seems unlikely. A small slug of water can make a diaphragm act weird and will clear after the water leaves the path but not right away.

a vis is called for I think since that part of the equation is in your control, you can possibly eliminate one issue but you don’t have any control over the other suspect.

 

[MrChen]

a vis is called for I think since that part of the equation is in your control, you can possibly eliminate one issue but you don’t have any control over the other suspect.

Good advice. I've mixed up the tanks, so I'm not sure which one it was now. I'll for sure be sensitive to the fact that this could happen again. If it happens again, I'll pull that tank aside.

 

[lexvil]

Good advice. I've mixed up the tanks, so I'm not sure which one it was now. I'll for sure be sensitive to the fact that this could happen again. If it happens again, I'll pull that tank aside.

I know it’s not an easy decision but I would have them all checked.

 

[rhwestfall]

If a tank is in for a fill, it is no big deal to drain, pull a valve, and take a peek.

If you explained the issue, most shops here would likely do it without any additional cost.