What is a scuba diving rebreather?
Who has never dreamt of staying underwater forever ? To swim with the fishes , to blend with them to the point where you could forget you weren’t meant to be an underwater animal ? I think it is every diver’s dream . This dream is now possible , at least for a few hours thanks to these machines : the rebreather
Recyclers , dangerous machines ?
For a long period of time, they had a terrible reputation. And to be honest, it hasn’t fully disapeared yet ! These machines are claimed to be complex , making the diver’s diving preparation long and hard. They are also known to be very dangerous !
What might have been true in the past, isn’t anymore. Recyclers are becoming more and more reliable
Therefore, their usage is getting more and more frequent. In fact, we can often see them in diving centers. This practice, back in the days only done by TEK diving expert, is nowadays seducing more a much broader audience.
A rebreather : what is it and how does it work ?
It simply is a portable gas factory.
The closed circuit rebreather is a machine that recycles a gas mixture which is then breathed in by the diver.
He breathes in what’s called a breathing loop.
Therefore, on the opposite of an opened circuit where the air, once inspired is lost once expired, the recycler will capture it and recycle it and introduce it into the breathing loop .
This mecanism greatly lowers the quantity of air needed for the saim dive.
Definition of a rebreather:
Allright ? Understood these basic principles ? I am now gonna explain that in detail !
The air we breath everyday is a gas mixture composed of 21 % of oxygene and 79% of nitrogene.
When using an opened circuit, the air blown out from our lungs goes to the second floor to get to the surface, making beautiful bubbles. This air, lost forever still has between 16 and 17% of oxygene. What a loss !! It’s a mess
In fact, we only consume 4 to 5% of the oxygene each time we brieth
Why don’t we use everything we can before making beautiful bubbles ?
This is where things get a little hard ! But stay with me here Our body needs a certain amount of oxygene to work properly. This rate can’t be too high or too low. Le pourcentage minimal d’oxygène à la surface doit être de 16%. Below this, we are in hypoxiaand the mixture isn’t breathable. 16% is therefore the minimal rate of oxygene a mixture should have at the surface. It also is the exact rate of oxygene that comes out of our lungs.
The goal of the rebreather, at least one of it’s functions, is therefore to reinject the oxygene consummed by the diver.
But that’s not all it does ! If we consume oxygene, we also produce C02, and that’s very bad for our body.
If the rate of C02 rises too high, the diver is at risk of an hypercapnial crisis. This is why, the recycler has a filter that’s able to filter the C02 that’s rejected from the diver.
Therefore, we can’t breath the same air for a long time as our organism metabolises the oxygene that’s in the air.
Another phenomenon involves a necessary air purification before breathing it in again
In fact, we consume 02, but, we reject c02. The rebreather has therefore a purifying function for the air loop by capting the emitted C02, and by holding the gaz from the viable loop for the diver by injecting the O2 cusummed by himself.
Here is the basic principle of all rebreather with closed circuits.
In fact, there are several types of closed circuit rebreather :
the eCCR (electronic rebreather)
the mCCR (mécanic rebreather)
the hCCR (hybrid rebreather).
The basic principle being the same for all closed circuit rebreather, the elements constituting it are almost identical on all machines.
Here is a sketch of the Inspiration rebreather :
We immediately notice the main components of the machine :
The fake breathing out lung : i
t is a bladder that is filled with the stale air exhaled by the diver.
this is the central part of the rebreather, which contains the soda filter capturing the CO2 emitted by the diver.There are 2 types of Canister : Radial and axial
commonly known as “cells”, these are essential elements in the operation of a rebreather.
the electronic part of the rebreather, 2 for the sake of redundancy. They analyze, independently of each other, the values given by the oxygen cells.
it is a sort of solenoid valve that the controller opens more or less long to top up oxygen in the breathing loop and maintain a constant PPO2.
it is a small bottle of 2L or 3L filled with pure oxygen. It is connected to the loop by the solenoid and a manual injector.
The fake lung:
it is the bladder which receives the “purified” air of the CO2 after its passage in the canister, enriched in oxygen after being analyzed by the cells.
it is the same bottle as the O2 block but filled with a diluent gas (air or trimix). This gas serves to maintain a constant volume in the breathing loop. The diver can inject diluent as needed using a manual injector.