Revo BOV questions

[tbone1004]

Thanks for your response. To quote from your response

"f you have a bad pack in the first then the second will catch it but the first scrubber is not being used completely so your risk of breakthrough actually increases if you are running long profiles"​

Can I ask why do you think this is the case? Bearing in mind that the whole dea of diving the rEvo is based on the top scrubber scrubbing all of the CO2 and the bottom one acting as a secondary scrubber to catch any residual CO2?

Cheers

What makes you say the whole idea of the revo is to use the top scrubber and the second to act as a parachute? That is not the "whole idea" of the unit. It's a common way the unit is used but then you can only treat it as a unit with a 3lb scrubber capacity instead of the 6lbs you are carrying.

 

[Peter10/50]

There are literally hundreds of pages of threads written on the effectiveness of a BOV on a CCR both on this forum and elsewhere. I would suggest if you want to learn about this piece of equipment just simply type in BOV into the search field at the top and start reading.

We all have our own views on them, and I use one on a rEvo. Re the rEvo BOV I understand it performs as per the EN 250. standard which I think bottoms out at 50M depth. But then is this depth even relevant or is the actual breathing gas density at depth more relevant??

I think it fine and useful to continue to have this discussion. Since I started diving ccr there have been many developments in equipment and thinking.

The dreaded CO2 hit seems the principle reason most give for running a BOV. I am not hearing of it happening although reporting and analysis seems worse than previously. A BOV will not improve WOB. I am under the impression that work of breathing is the most important factor in CO2 generation. The newer BOV breath better but still are bulky and affect breathing effort negatively. Good luck breathing on a BOV when faced with a caustic cocktail.

There may be other good reasons for running a BOV. Injecting gas into the loop when otherwise constrained makes sense to me and there are now BOV models that have MAVs attached. They look bulky and heavy but I have not tried one.

There are good reasons for all of us to consider our options. Lots of advanced scuba instruction remains more tribal than technical. It is always good to look around and reflect on our choices and just what underpins them.

 

[tbone1004]

@Peter10/50 bulky is actually good when looking at the BOV's because they can increase air space in the second stage enough to offset the weight and as a result are more comfortable. The Poseidon BOV is actually really comfortable in the water, especially once you put a neoprene chin rest on it. It looks very big but because it is injection molded instead of machined it is very light weight in practical use

 

[Peter10/50]

@Peter10/50 bulky is actually good when looking at the BOV's because they can increase air space in the second stage enough to offset the weight and as a result are more comfortable. The Poseidon BOV is actually really comfortable in the water, especially once you put a neoprene chin rest on it. It looks very big but because it is injection molded instead of machined it is very light weight in practical use

Until you scooter with it. Lol.

 

[tbone1004]

Until you scooter with it. Lol.

see note about the neoprene chin rest. No discomfort with 3-4hrs on the trigger and I suffer from TMJ so am very sensitive to jaw fatigue. Without the chin rest it's very rough but no issues with it.

 

[Wibble]

You can only dump liquid out of the exhale side by getting it out of the loop and somewhere else, check valve will stop it from going back into the mouthpiece. Barrel rolls work well for this.

It’s really annoying when there’s enough water next to the exhale mushroom to pass back into the mouthpiece and give a rather wet breathe. The "hero" move shakes it down into the exhale lung and flat trim tips it back. Having a half cloth rolled up under the exhale loop mops up some of the water.


What’s needed is a little "thumb pump" connected to the exhale side of the DSV/BOV. If water collects, press the "thumb pump" a couple of times to throw it overboard. Sigh, if only.

 

[flymolo]

It’s really annoying when there’s enough water next to the exhale mushroom to pass back into the mouthpiece and give a rather wet breathe. The "hero" move shakes it down into the exhale lung and flat trim tips it back. Having a half cloth rolled up under the exhale loop mops up some of the water.


What’s needed is a little "thumb pump" connected to the exhale side of the DSV/BOV. If water collects, press the "thumb pump" a couple of times to throw it overboard. Sigh, if only.

With a bov can close the loop and spit it out of the second stage of the bov

 

[tbone1004]

It’s really annoying when there’s enough water next to the exhale mushroom to pass back into the mouthpiece and give a rather wet breathe. The "hero" move shakes it down into the exhale lung and flat trim tips it back. Having a half cloth rolled up under the exhale loop mops up some of the water.


What’s needed is a little "thumb pump" connected to the exhale side of the DSV/BOV. If water collects, press the "thumb pump" a couple of times to throw it overboard. Sigh, if only.

barrel roll. Was taught to my on the Meg in my initial Mod1 course. On the Meg it's counterclockwise, but on everything else you do a clockwise roll. Go slow and shake/extend the loop hoses while you're doing it and it will get it to drain into the counterlung. Start slightly head down then when you get upside down you want to go slightly head up with anything that is BMCL so everything drains to your back and into the lung. Very effective. I'm a pretty wet breather so I have to do it every 30ish minutes or so after the first hour on the loop.

@flymolo I think he's talking about the stuff that is on the outside of the check valves that causes the gurgling on exhale. No way to get it back past the check valves if they're doing they're job so have to send them along the gas path and into the lung.

 

[flymolo]

barrel roll. Was taught to my on the Meg in my initial Mod1 course. On the Meg it's counterclockwise, but on everything else you do a clockwise roll. Go slow and shake/extend the loop hoses while you're doing it and it will get it to drain into the counterlung. Start slightly head down then when you get upside down you want to go slightly head up with anything that is BMCL so everything drains to your back and into the lung. Very effective. I'm a pretty wet breather so I have to do it every 30ish minutes or so after the first hour on the loop.

@flymolo I think he's talking about the stuff that is on the outside of the check valves that causes the gurgling on exhale. No way to get it back past the check valves if they're doing they're job so have to send them along the gas path and into the lung.

Oh, true. Not sure what to do on a revo but on my unit I just fold the exhale hose together like an accordion and blow it into the counterlungs

 

[cathal]

What makes you say the whole idea of the revo is to use the top scrubber and the second to act as a parachute? That is not the "whole idea" of the unit. It's a common way the unit is used but then you can only treat it as a unit with a 3lb scrubber capacity instead of the 6lbs you are carrying.

Well its just that rEvo seem to advocate this method of using the scrubbers:

"In practice the area where the gas flows into the scrubber will be the first part to be saturated. The other end of the scrubber will never be saturated, because the scrubber will be changed before it is completely used. You never now exactly how far the scrubber is used: all the time a large amount of unsaturated absorbent must be available as safety-margin for a sudden increased effort"​

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"Drawing of scrubber saturation after one and two hours diving: after two hours the scrubber at the inhale lung is not saturated yet: there is always a substantial amount of unused scrubber available in case of extra CO2 production (hard work). However the scrubber will be changed, because the scrubber on the exhale lung is nearly exhausted: so now nearly no unused scrubber will be thrown away."​

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"In practice, the partial changing of the used absorbent, results in an increased absorbent-use time by at least 50%, without affecting the safety margins, compared with a single scrubber where the complete amount of absorbent is changed in one time. If only the same total use-time of a single scrubber with the same amount of absorbent, is followed, the safety margins are increased considerably. "​