Question SCR Semi Closed Rebreather

[Robert H. Diver]

Yes thats correct. I was mostly looking for more info on SCRs when I made my original post, I think in my mind I have shifted from the question "Is an SCR right for me" to "What is an SCR and what is it a tool for"

I don't know anything about SCRs and the info on the internet is a little scarce so that's what prompted me to post here.

From this thread I have gathered:
1) I should get into Nitrox
2) SCRs are more a "gas extender" than a CCR (Im sure I'm explaining this wrong).
3) SCRs are still limited by NDL, I'm not too sure what that means when compared to a CCR.


I hope this response doesn't come off as being a jerk or immature. I genuinely enjoy learning new stuff even if I don't use the skills.

You definitely aren’t being a jerk. You don’t know what you don’t know. It can’t hurt to ask questions…I love learning new things as well, that’s one reason why I’m on here almost everyday reading new and old threads.

 

[MichaelMc]

The best value, especially for intermittent diving before taking leap to CCR, is the combination of a nitrox course and a decompression procedures course with bigger tanks in my opinion

A light, back gas, deco class would also be an option. A simpler class and simpler in the water than full accelerated deco. But definitely nitrox first.

 

[Heat Miser]

From this thread I have gathered:
1) I should get into Nitrox
2) SCRs are more a "gas extender" than a CCR (Im sure I'm explaining this wrong).
3) SCRs are still limited by NDL, I'm not too sure what that means when compared to a CCR.

1) I should get into Nitrox

Yes its a very simple course, which in my country can be run after work (2-3 hours) of theory with no need for a practice dive. And will lengthen you NDL's or simply make you less tired after a dive.

2) SCRs are more a "gas extender" than a CCR (Im sure I'm explaining this wrong) and SCRs are still limited by NDL, I'm not too sure what that means when compared to a CCR.

SCR's are way of recycling Nitrox to extend the dive time and reduce gas usage, but just like on Open Circuit your PPO2 is variable dependent on your depth in the water column. With CCR's you have a fixed or constant PPO2 (which on a e-CCR is maintained by a solenoid firing from a regulator on an O2 bottle). Because of the higher average PP02 on a CCR you end up with longer NDL's or less Deco time then on a SCR with the same dive profile.

(I disagree with) and despite what Mares Horizon say in their marketing material here:

"Within operational limits (up to 40m) the unit provides decompression obligations like that of a closed-circuit rebreather"

SUBSEQUENT EDIT

Yes SCR have a place, perhaps in Photography etc. or If your not going to dive say 50 hrs a year to start with and subsequently 25 hours a year to maintain your CCR skills then maybe SCR is for you.

I have tried to get my wife to look at one, she is 43 dives AOW/Nitrox ... her argument ... she doesn't want to dive anything she has to build first.

 

[GiraffeMarineSalvage]

(I disagree with) and despite what Mares say in their marketing material here:
"Within operational limits (up to 40m) the unit provides decompression obligations like that of a closed-circuit rebreather"

Mares has pretty crafty marketing materials on that one! I can see how "dual gas possibilities – with the option of attaching a second cylinder with a higher O2 concentration for accelerated decompression" could be "like" that of a CCR or accelerated OC deco...). Isn't freediving "like" CCR too (its done underwater, uses a mask and fins, is a silent diving experience, etc, etc..).

 

[BoltSnap]

Hey all I am looking for some basic information on SCR units. I am looking for extended bottom time within Recreational diving limits(my current depth limits are 130FSW and no decompression). I'm currently diving single back gas (AL62, LP72, HP100) and sidemount (I have a set of both LP72 and LP50 for side mount). I was talking with a tech in my LDS and he mentioned I may want to look into SCR units for extending my bottom time within Recreational limits. I do have desire to eventually get into tec for deeper wreck dives (one is the Infadel in 150FSW and a second is UB88 in 190 FSW), I do know I want to wait until my kid(s) is/are older.

I don't really have many friends that dive rebreather at the moment but I do know there is a local community but im not a part of them yet.

Thoughts on going with an SCR at this point in my dive career?

This guy just started his SCR journey, he may be of interest to you with his different perspective:

https://youtube.com/@UKDiver

 

[Heat Miser]

This guy just started his SCR journey, he may be of interest to you with his different perspective:

https://youtube.com/@UKDiver

Yes they have a place, perhaps in Photography etc. or If your not going to dive say 50 hrs a year to start with and subsequently 25 hours a year to maintain your CCR skills then maybe SCR is for you.

I have tried to get my wife to look at one, she is 43 dives AOW/Nitrox ... her argument ... she doesn't want to dive anything she has to build first.

 

[Wibble]

SCR (Semi-Closed Rebreather) as a gas extender…

This is a machine where you breathe oxygen rich (nitrox) gas into a closed loop containing a CO2 filter (scrubber), counter lungs (literally a bag) and back into the mouthpiece. This causes the oxygen in your breathing gas "loop" to drop as your body consumes the oxygen, requiring some new nitrox gas to be periodically injected into the loop to bring up the oxygen levels and the same amount of "exhaust" gas is released from the loop as bubbles to keep the overall amount of gas in the loop the same.

This will mean you use a lot less gas (one third to one fifth) than if you were blowing bubbles from a normal Open Circuit regulator. This means you can dive much longer for a given amount of gas, i.e. you extend the range of the gas you carry.

The major drawback is you add massive complexity for very little benefit.

A Semi-Closed Rebreather (SCR) is very similar to a fully Closed Circuit Rebreather (CCR). The difference is the CCR continually monitors the oxygen levels and will add (inject) pure oxygen to counteract the reduction in oxygen as your body metabolises it (your body consumes oxygen and exhales Carbon Dioxide which is removed by the scrubber). A CCR doesn’t release gas from the loop -- no bubbles.

Thus a CCR uses even less gas than a SCR. It only needs to inject the oxygen your body uses which is about one to two litres of oxygen a minute (or in America one to two cubic feet of oxygen every 15 minutes) so only needs tiny tanks, even for a very deep or long dive.

A SCR can use more simple electronics than a CCR. However, a SCR has all the complexities, usage difficulties, preparation overheads, emergency protocols and training requirements of a CCR for virtually no specific benefits and without the flexibility of a CCR.

Hence SCR units are extremely rare and CCR units are very common.

TL; DR
Virtually nobody uses a Semi-Closed Rebreather.


Edit: Changed "Nobody uses an SCR" to "Virtually nobody uses an SCR". Hopefully this will keep the People's Popular Front happy.

 

[happy-diver]

Menu Homebuilders

How nice will it be when cheap little used Horizons hit the market screaming for conversion

 

[grantctobin]

TL; DR
Nobody uses a Semi-Closed Rebreather.

The WKPP, OCDA, a couple of KUR, and all users of the Tres Presidentes and similar units would disagree. They’re a niche item, and the wrong path for OP, but your post is silly and errant.

Then there’s the Drager series, the GEM, and the pockets of Horizons (hopefully some of whose features make it to the REVO4).

 

[Heat Miser]

Then there’s the Drager series, the GEM, and the pockets of Horizons (hopefully some of whose features make it to the REVO4).

Are ther Revo4 plans confirmed @grantctobin?