Diving MCCR beyond depth limits?

ardhill

Hi

I know that some people dive their MCCR's below the manufacturers depth limit. I was wondering how they do it?

I assume the limit for most of the MCCR's is 80m and my limited understanding is that this is due to the IP of the reg. As the IP is fixed on a Rebreather and doesn't change with the ambient pressure like an OC reg does, how do you get your RB to give you an accurate mix below the depth where the reg is no longer able to supply gas? Do you simply run the mix totally manually i.e. press the green 'keep me alive' button more often to maintain the desired PPO2?

I am still trying to understand the workings of the units, so forgive me if my presumptions above are incorrect.

Thanks
.

__________________
Paul

(Note: I currently don't dive a Rebreather, but dive OC. So if anything I say about breathers sounds suspect - it probably is)

Ben Field

No need to "bodge" the KISS, just adjust IP and orifice to suit the depth or take a compensated first stage O2 addition system in addition to the standard MAV system.

Depends, which MCCR are you trying to take to what depth?

__________________

Beware Fridge Suck

ardhill

I have heard of KISS units, Copis Megs and rEvo units being dived below 80m.

The majority of my diving would be within the depth limits, but occasional drops to say 100m ish (there are a few wrecks in the 90-100m in my sights).

At present, I also prefer the look of MCCR rather than ECCR. This may change, but I am interested in the options available. I am also interested in understanding more of 'how' it works.

Thanks

__________________
Paul

(Note: I currently don't dive a Rebreather, but dive OC. So if anything I say about breathers sounds suspect - it probably is)

Digger

Paul,

Most MCCRs are capable of 100m. And they should be, the orifices to run at 11 or 12 bar are easily available. The KISS and other units are rated to certain depths, but it seems that is more to do with manufacturers liability than the units not being able to perform at that depth.

I don't know about the Revo and some other units, but you won't have a problem with a KISS to 100m. Below 100m it's not the ideal unit for the dive. They can be modified with manual adds or with adjustable needle valves etc but they are modifications. If you have plans on doing much diving below 100m then many of the MCCRs aren't the right unit for the diving you are planning. That's how I see it anyway.

My unit's for sale, and will do 110m no problem. Feel free to PM me

Digs.

ardhill

Thanks for that Digger

You are of course one of the people I know have gone there on a KISS.

I know you are selling your unit, but the bank says NO! Really, I am looking at getting a unit next year, this years money is all spent - plus some.

So, the unit may go there out of the box, otherwise adjust the IP and the orifice flow as appropriate - that doesn't sound a botch up for an occasional dive to those depths.

I know Paul - rEvo's Daddy has done at least 121m on one.

__________________
Paul

(Note: I currently don't dive a Rebreather, but dive OC. So if anything I say about breathers sounds suspect - it probably is)

wedivebc

With a copis meg it is a simple matter of carrying a seperate oxygen cylinder with a normal 1st stage and plug it into your O2 bypass at depth. Or just leave it plugged in for the duration. This tank could also be part of your bailout gas.
The kiss is a little more complicated because you would have to plug in an offboard port somewhere.

__________________
Cheers,

Dave....

Man is the only animal burdened with the knowledge he will eventually die

paulraymaekers

with an IP of 11 bar, and some restrictions, the rEvo supplies oxigen up to 105 meter easely
why 80m: better not to dive on the limit of a unit, so indeed some kind of liability
the scrubber is not the problem for a higher depth

I know some people dive the rEvo with an 0.0030 orifice, and an IP of 14.5 bar... so this keeps giving oxigen up to 135/140 m...

for testing, (AND ONLY FOR TESTING!!!) so we do not advise to do it, with the 32 beta units over 300 dives were done below 80m
you can do it different ways: eigther pumping up the IP a bit, even with a 0.0035 orifice, the flow will be a bit high during ascent, but once on bottom and during descend you need more oxigen, so that is not a problem
you can also pump up your PPO2 when arrived at 100m, (say to a max of 1.6) then do your dive to 120, say for 10 minutes, and come up to 100m where again you can pump up your PO2 to normal (1.3 or less)
during those 10 minutes, your PO2 will not fall dangerously,... and if it would be the case, you can always take some dil to increase your PPO2 again..
otherwise a separate small ox tank with a man add button, and a standard first stage on it: the cmf will not work anymore, but you can add manually..

see, if you know how to dive a mCCR, not such a big deal... BUT DON'T DO THIS YOURSELF, WE ONLY DID IT FOR TESTING !!!!!!

paul

__________________
www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

ardhill

I appreciate all the replies.

So, there are ways and means without getting too complicated and most importantly for me, the units I am most interested in can all do 100m without much fuss.

Thanks
.

__________________
Paul

(Note: I currently don't dive a Rebreather, but dive OC. So if anything I say about breathers sounds suspect - it probably is)

wedivebc

The official answer is to dive within the limits of the unit's manufacturer. The fact the Rebreather World is loaded with homebuilders, designers and adventurers who pushed beyond what is considered reasonable limits. Many are here to enlighten us with their stories others alas are no longer with us but we learn something from each.
Play smart and play safe and I am sure you will get to where you want to go soon.

__________________
Cheers,

Dave....

Man is the only animal burdened with the knowledge he will eventually die

RichClark

Hi Paul,

Do you know what 1st stages people are using? I thought that the DS4 spring goes solid around 13 bar.

Cheers

Rich

__________________
The more I learn about women, the more I want to go diving... just don't tell my wife I said that

To taste something a little different, try http://www.thechillikitchen.co.uk