It finally happened - my CCR tried to kill me

[Efka76]

@stuartv , thanks for sharing. It was very interesting to read. Your story proved to me once more that CCR diving is definitely not to me. Too complicated, too high risks involved.

 

[DiverDiverRUOK]

No. The rEvo Closed Checklist ends with a negative test, but no positive test.

This is inaccurate - the rEvo closed checklist has the "Overpressure test - OPV?" line which is meant to be a positive pressure test and checking that the OPV is not stuck closed. The checklist is not great at explaining that, but that step should be the positive pressure test (overpressure test) where you fill the loop, trap an overpressurization in it, wait at least 1 minute, and then check to see that it held the positive.

Not saying that a positive check definitely would have caught the issue, but you should be doing a positive during the Dil side of the closed check (Closed Check B).

 

[lermontov]

thanks Stuart - another indicator of the lid not closing properly is the threaded rod not coming through far enough for the wing nut thingy to fasten down - my regular check is the battery box stopping it from seating properly

 

[Wibble]

On my Revo MOD1 I replaced a mushroom valve which entails removing the jubilee clip from the DSV to remove the hose.

Progressively over the next two days I found more and more water leaking into the unit. Was good practice at first with the "hero" manoeuvrer to clear the loop, but due to my very flat trim (an OC habit that won't go away), liquid from the exhale lung runs into the exhale side of the loop and water will run back in as one's exhaling. Eventually I got a full mouthful of water and immediately bailed out. Not nice, but hey, great practice.

Binned the dive to investigate and spent ages looking for the leak. Through good fortune we tried tightening the DSV jubilee clips to find them a little loose, i.e. not tight enough.

Obviously no cocktail as the unit was flat in the water and the scrubbers are "out" of the puddle.

As an aside, some water had probably splashed on two of the three sensors on the Petrel controller resulting in a voting error -- the one good cell matched the other two cells on the Nerd. Carried on the dive as it was shallow and eventually the two cells settled down -- dried out?

On all my subsequent dives, have never had any water ingress; just normal lung butter.


Point I'm making is that Revos are particularly sensitive to water ingress into the loop especially if you dive flat or go head down where the water flows to the top of the unit and down the breathing hoses to the DSV. In your case, if you're in more of a head-up position, more liquid may accumulate in the lungs before you notice it.

Still love the unit though! So many other benefits that this foible can be overlooked.

 

[tbone1004]

I hope @Dsix36 pipes in as he has a lot of hours on the Revo.

My takes on this. Lady Luck is a ~100ft wreck and I don't disagree with 18/45 as a bailout gas if it was also dil, but would probably have used 30/30. Either way if you had planned deco a 40 of O2 or 50% would probably have been a good idea, but low priority.

Staying on the loop matters in a cave, and it matters when you are doing deep expedition/project diving where you really don't want to bail out if you don't have to due to limited filling resources. For normal open water diving, it's not a priority to figure out and you haven't been trained on what to do to stay on the loop yet, so I'd hold out on that.

I disagree that positive and negative checks won't ID small leaks. They can and will, but ONLY if you have an ambient pressure sensor. Thankfully your unit has 5 of them, and normal rebreathers have 3. When you do your positive and negative checks, watch the mV or ppO2 and you can see what the internal pressure is doing. I bet that it would have caught that leak, small though it was. I would recommend adding that in to your pre dive checklist

 

[Rose Robinson]

I've been feeling pretty lucky to never have felt like I'd had an "oh, ****" moment while diving my rEvo. That is now behind me.

Stuart,

Glad to hear you're OK.

I have attended, several RB clinics, and have dove as many units, the rEvo not being one of them. The rebreathers I have had restricted ''try dive'' experience with are the DR Optima, Hollis PRISM ll, and the Vobster Red Bare. Of the three, I did like the Red Bare very much.

On the rEvo, what is the established duration for the positive/negative pre-dive checklist tests, duration being time in minutes.

I'm not rebreather certified on any unit, but in my mind, the longer a unit holds what is basically a ''no leak'' test the better.

Thank you in advance for your response to my inquiry.

Rose.

 

[Heat Miser]

Those little feet can be a pain to mount correctly. I have dived once or twice with them not being mounted fully, with no great effect. However, I can see that a loose tank banging against the scrubber lid, would not bet conducive to keeping it airtight. Thanks for sharing, glad your OK. Don't put the hairdryer on the wet O2 cells, let them dry out naturally.

 

[wedivebc]

So your rebreather gave you an indication that things weren't right so you bailed out. Good job. But then you went back on the loop? I don't think it was your rebreather trying to kill you at all.

 

[davehicks]

I disagree that positive and negative checks won't ID small leaks. They can and will, but ONLY if you have an ambient pressure sensor. Thankfully your unit has 5 of them, and normal rebreathers have 3. When you do your positive and negative checks, watch the mV or ppO2 and you can see what the internal pressure is doing. I bet that it would have caught that leak, small though it was. I would recommend adding that in to your pre dive checklist

Can you explain this in more detail? I've not heard of using the sensors to monitor pos/neg during check out.

 

[wedivebc]

I disagree that positive and negative checks won't ID small leaks. They can and will, but ONLY if you have an ambient pressure sensor. Thankfully your unit has 5 of them, and normal rebreathers have 3. When you do your positive and negative checks, watch the mV or ppO2 and you can see what the internal pressure is doing. I bet that it would have caught that leak, small though it was. I would recommend adding that in to your pre dive checklist

Very good advice. I also crush my hoses (not older meg hoses, they are too stiff) to indicate pressure drop.