“Fairly” Uncontrolled Ascent - Please help me understand what went wrong

[KristenK]

Hello everyone, I’m on a dive trip in Turks and had two upsetting dives this morning. I am a good diver, although only 120 dives, and can’t figure out what happened. I think it was equipment related. I have an Aqualung Micron and a Cressi BCD. I’ve been diving with both for 5 years without any problems.

Dive started fine. At about 45 mins the first dive and 35 mins second dive I started ascending. I dumped all my air, using dump valves and the shoulder dump. I squeezed the bcd the best I could to get air out. Nothing worked. I grabbed the safety stop bar and even that wouldn’t keep me down.

I will say my second stage and octopus free flow fairly easy. I have no idea if this has anything to do with it.

My weights are fine. I even added 2lbs the second dive. Sank like a rock and knew I was overweighted.

No one on the island services equipment (that’s not their own rental gear.) I’m switching to rentals tomorrow. But meanwhile my confidence has been shaken and I have 3 more dive days to go (and Philippines in January.) Not fun.

Thank you for your knowledge and help!

 

[rx7diver]

Stuck power inflator, maybe?

When was your regulator last serviced? Did the tech check the intermediate pressure?

rx7diver

 

[KristenK]

Stuck power inflator, maybe?

I don’t think so. I just examined it and it seems fine. But maybe when underwater it sticks???? Everything looks clean.

 

[MidOH]

Well......you'd hear the inflator.

I'm going with empty Al80. They can get floatier than we think.

 

[KristenK]

Stuck power inflator, maybe?

When was your regulator last serviced? Did the tech check the intermediate pressure?

rx7diver

Last serviced 2 years ago. I didn’t ask specifics.

 

[rx7diver]

Now that you're back home, you might take your gear into the shallow end of the swimming pool and see if you're able to have the same thing happen again.

My early scuba instruction had us oral-inflating during our pool dives--wouldn't allow us to use the power inflator during our pool sessions. A very long course (16 weeks), so we all were very comfortable diving using oral inflation only by the time the course ended. If I suspected, during a real dive, that my power inflator was leaking, I would quick-disconnect it and continue the dive using oral inflation. (This is a necessary skill when diving very cold water.)

rx7diver

 

[SlugLife]

One additional thing to look into, might be air-trapping in the BCD. Though that doesn't usually cause any "sudden" increases in buoyancy, and can be neutralized by finning downward.

But maybe when underwater it sticks????

In my experience, when things (doors, handles, buttons, etc) start to stick, they don't stick every time or all the time. Perhaps being at a different angle, under pressure, etc is just enough of an edge to make it stick. (I'm not saying it is or isn't the inflator getting stuck, just thinking out-out)

 

[MidOH]

Are bcd inflator quieter than bpw k?

On my bpw's the inflator sound is loud and obvious. I hear that, and I'm disco'ing immediately.

 

[Kendall Raine]

I don’t think so. I just examined it and it seems fine. But maybe when underwater it sticks???? Everything looks clean.

Assuming you're properly weighted to start with, sounds like a stuck inflator. They can be sneaky and stick intermittently or slow filling. If your BCD is five years old it's entirely possible the inflator mechanism (or at least the internal cartridge) needs replacing. I wouldn't assume the inflator was replaced when your regs were serviced unless you know otherwise. From what I can see Cressi uses its own (rather than generic K valve) inflator mechanism. That's too bad since they can be harder/more expensice to find/replace. You may need to wait until you get home to get sorted but I strongly recommend you go with a generic K valve inflator (and compatible hose assembly) since they're ubiquitous-cartridges are $15-or carry a spare Cressi unit on your next trip. I change out the K valve inflator cartridge before every big trip and carry a couple of spares.

In the near term-before your next dive-connect the BCD to the LPI hose and hit the up button hard for two seconds and release. Wait ten minutes. If the BC keeps inflating, even a little, it's a stuck inflator. You won't necessarily hear it if it's a slow fill. If it doesn't fill at first, it could be an intermittent stuck inflator. Try the test a dozen times. After each give it a while to see if the BC keeps filling. Trying another reg on your BCD is also one way to test whether the inflator is the problem. If it is, swap out the inflator if possible. Don't bother replacing/servicing the o rings. Just chuck the inflator (or at least the internals). Swap them out from time to time prophylactically-hint: your service tech will not likely do this unless requested.

Free flowing regs are another matter. If the seconds are free flowing it's likely they are either hot tuned (below spec) or the IP is above spec, or both. BTW, even if the IP is out of spec, it's not likely the cause the uncontrolled BCD filling since second stages would likely free flow massively before that. Besides, the buoyancy problem occured well into the dive. If the problem was an out of spec reg it would show up late in the dive they way you describe. However, it's possible you have multiple problems (some combination of first stage IP out of spec, second stage cracking pressure out of spec, stuck inflator). At the least, I would have your IP and seconds checked and adjusted if out of spec.

 

[Kendall Raine]

Sorry. Meant to say "If the problem was an out of spec reg it wouldn't show up late in the dive they way you describe."