Recycler and Rebreather diving

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 recyleurs

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.

recycleur diving

A recycler :  what is it and how does it work ?

“It simply is a portable gas factory.”

The closed circuit recycler 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 recycler

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 azote.”

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 recycler, 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 recycler 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 recylers with closed circuits.

In fact, there are several types of closed circuit recyclers :

  • the eCCR (electronic recycler)
  • the mCCR (mécanic recycler)
  • the hCCR (hybrid recycler).

The basic principle being the same for all closed circuit recyclers, the elements constituting it are almost identical on all machines.

Here is a sketch of  the Inspiration rebreather :

sketch of  the Inspiration rebreather

We immediately notice  the main components of the machine :

  • The fake breathing out lung : it is a bladder that is filled with the stale air exhaled by the diver.
  • The Canister: 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 :

    1. Radial
    2. axial.
  • O2 probes: commonly known as “cells”, these are essential elements in the operation of a rebreather.
    The role of the cells is to control the PPO2 of the breathing loop at all times. They are generally 3, but some recyclers have 5.
  • Controllers: 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.
  • The solenoid: 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.
  • Block O2: 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.
  • Diluent block: 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.


The benefits of the recycler

Rebreather diving has many advantages over open-circuit divingLa plongée en recycleur comporte de nombreux avantages par rapport à la plongée en circuit ouvert.

Here are some of them :

  • Silence: This is the first benefit that comes to mind.
    Indeed, diving without bubble allows you not to  scare the marine fauna and it’s a real asset for the approach and the observation, especially for the underwater photographers and videographers. We can observe behaviors that are usually impossible to see in scuba diving.

    “Using a rebreather is  really the world of silence described by Commander Cousteau”

  • Increased autonomy: This is the second significant advantage of using a recycler
    This type of dive provides a great autonomy of operation and no matter what depth you are diving at.
    We are no longer hurried, by the pressure of the bottle that is getting closer and faster towards the reserve

    Using a rebreather, we’ve got time.

    “Who has not dreamed of doing 50 minutes at 30m deep without having any  extension bearings? The recycler allows it.”

  • Decompression optimization: This is the third advantage of the rebreather. The gas breathed in the loop is constantly changing according to the depth. We breathe an optimized mix at any moment of the dive. This is a huge advantage when it comes to decompression times, which are greatly diminished.
    It’s also a huge advantage in terms of safety (which does not exclude the risk of accidents)

  • Hot and humid air : It’s a lot more confortable, especially in cold water.
    The chemical reaction that allows it to capture the CO2 emitted by the body creates heat and water vapor. For the greatest fullfillmentof our lungs.


The disadvantages of recyclers

Yep, there are some disadvantages compared to conventional open circuit diving.

To my mind, they are quite small considering the benefits offered.

  • Investment: The first disadvantage is the recycler’s investment cost and training t, which will vary depending on the chosen machine and options.

“It takes between 6000 and 10 000 € to purchase one.”

  • The size : If you dont’ want to dive heavy, forget about it
    Eventhought these machines are getting smaller and smaller, such as the rEvo or the Innerspace’s  Pathfinder the size is bigger than when using an OC ( open circuit ), especially because of the bail out blocks.                     

    “This weight will dramaticaly affect your ease and stability underwater, especially at the beginning.”

  • The preparation : rig your block for around 5 minutes, but preparing your recycler requires a  bit more time.
    Eventhought it doesn’t take hours, the preparation of the recycler for the dive requires attention and time.

    Around 15 and 20 minutes .
    The machine’s preparation implies a bunch of tests ( waterproofing, cellules control, gaz analysis, etc….) 
    None of these tests should be neglited !
    If a test isn’t concluant, don’t go to the next one before solving the problem.

    “Recycler diving requires a bit more time, attention and efforts than regular, open circuit hobby diving. The divers who are always late and quickly rig their blocks on the boat while cruising aren’t the type of people that are able to go recycler diving.”

  • The lost of ballast lung : I put it in the drawback section, but personaly, as a photographer, I don’t think it is a real one !
    Maybe thanks to experience.
    Of course the perfect  stabilisation is a lot harder to get, but once stabilised, you won’t more an inch

Recycler and Rebreather diving

The recycler, another way to dive, and a true philosophy

Diving with a recycler is very different from diving with an open circuit.

Whether you have got 200 dives behing your back ( eventhought you need to be at ease underwater ), or 10000, it won’t matter at all.

“In both cases, you will have to start from the beginning again.”

Good to know :

The stabilisation

The lost of a ballast lung requires a big stabilisation effort.
In an open circuit, the diver can compensate the stabilisation problems of his vest using the ballast lung, most of the time, he does it without even realising it.

Using a recycler, it’s not possible due to the volume that constant.

Indeed, the expired air goes to the fake expiratory lungs, and the inspired air comes from the fake inspiratory long. The volume  being always simlir, we can’t manage our buoyancy using our lungs

The lost of the ballast lung is therefore an handicap for young divers in close circuit, so much that a perfectly aquired stabilisation isn’t so any more.

“Personally, it took me 6 months, diving once a week to perfectly master the recycler’s stabilisation, ( especially as a photographer, where it needs to be perfect “.

On top of that, you have 2 volumes to take care of  :

  1. The stabiliser vest
  2. The volume of the fake lungs
  3. AND even 3 volumes if your suit is waterproof

If evolve at a constant depth, you won’t need to play witht he injectors or the purges in order to maintain yourself in a stable position.  

On the other hand, the depth changes will have an impact of the loop’s volume.

  • The deeper you go, the higher the pressure, and you will be obliged to inject more diluant into the loop.
  • Conversely if you go back up, the rise of gaz volume present in the loop will have to be evacuated by the nose.
    More over the PPO2 will drop, which will cause the soleinoide to activate and poor out some O2.

“You guessed it, it will take some time before being able to master each and every of these volumes”


Managing the dive

This is where the diving philosophy radically changes ! In fact, the reasoning isn’t the same at all !

In an open circuit, here is the question we ask ourself : How much air have I got in the block ?

In a recycler : What am I breathing ?

The autonomy countdown is not longer felt, eventhought it still exists.

We have got time !! Even in median space, between 30 and 40 M we have got time.

Without getting into TEK dives, which, at this depth, gives all the meaning to the recycler

The fact that we have got that much time allows us to rediscover the sites we thought we already knew by hear.”

Recycler and Rebreather diving

Why does the recycler optimises the decompression ?

It’s a question that I often get asked.  In order to reply, we need to talk about oxygene toxicity, and to understand the notion of partial pressure.

Oxygene is toxical !

I often hear in TV reportages, the speaker talking about oxygene bottles when divers are on the screen.

This is totally wrong.

In most of the cases, it’s bottles of air like the one you are currently breathing.

They are NOT filled with oxygene

Here is why :

“The oxygene, essential element of life, is paradoxally very toxical at certain pressures.”

The human body is perfectly adapted to our natural envirronement.

Good to know :

  • a pressure at sea level of 1030 HECTOPASCAL
  • and an atomosphere ( air ) composed of 79% of azote, 20.9 % of oxygene ( and a few rare gazes ).

The rest of this, we will simply it by saying the air is composed of 79% of azote and 21% of oxygene.

  • Azote :1bar x 0,80 = 0,8 bar PPN2
  • Oxygène :1bar x 0,20 = 0,2 bar PPO2

It’s called the DALTON law


These conditions change while diving !

At 10 meters deep, the ambiante pressure is of 2 bar (1 bar of atmospherical pressure + 1 bar of water collumn pressure).

At 20M, it’s 3 bars, at 30m it’s at 4 bars, and goes on and on…..

“The partial pressures therefore evolve according to the depth.

At 10 m we get :

  • Azote :2bar x 0,80 = 1,6 bar PPN2
  • Oxygene :2bar x 0,20 = 0,4 bar PPO2

At 20m :

  • Azote :3bar x 0,80 = 2,4 bar PPN2
  • Oxygene :3bar x 0,20 = 0,6 bar PPO2

It’s good to know that the partial pressures of azote (PPN2) and of the oxygene ( PPO2), have some critical steps that shouldn’t be trepassed.

The PPO2 is fixed at 1.6 bar ( the lenght of exposition is also limited ) and the PPN2, is at 5 bars.

By breathing at a 10m depth, we breat air at a pressure of 2 bars.

Our metabolism consumes oxygene.

Azote is diffused in our organism so that it is balanced ( equi-pressure ) with the ambiant pressure.

When coming back to the surface, the extra azote in our body has to escape in order to keep the balance. This is the reason we do compression bearings.

In a recycler, the PPO2 is managed by the machine.

Generally, it’s set to 1,3 Bar, and that no matter the depth of evolution. There is a composition modification of the gaz according to the depth we are at.

Here is a comparative board of a gaz breathed in with a recycler at a fixed 1.3 bar PPO2, compared to the air that would have otherwise been breathed in with an open circuit :


We notice that when using an open curcuit, the gaz proportion stays the same, no matter the depth. This phenomenum is normal as the composition doesn’t change.

Only the pressure varies

On the other hand, when using a recycler the gaz mixture varies according to the depth.


“We have an evolutive Nitrox.”

The gaz breathed is optimised according to the depth. We notice that there is less azote with the recycler’s mixture. Our organism satures less, and therefore the decompression bearing time are reduced.



At 50M deep, the expired mixture has almost the same composition as the air. Tis induces maximum rebreather diving depth with an air diluentr. This limit is due to 2 phenomenums :

  1. The air viscosity : the deeper we dive, the more the air density rises and the harder it is to breath.
  2. The narcose : below 60m, the recyler will keep the PP02 level at 1.3 Bar, but the PPN2 will keep rising.
    The breathed mixture is very narcotic, as there is a lot of azote.


Is diving with a recycler more dangerous than diving with an open circuit ?

At this question, I feel like I need to say : Yes…. but no !

Sure there is more technology in a recycler. More electronics, more joings, a waterproof circuit…. so potentially more breakdownds that Open Circuits.

But we have a couple of safety bottles !

“Haha, we aren’t that crazy after all !”

On the other hand, the breathed in gaz is optimised for decompression, therefore, we greatly minimise the decompression risks.

Therefore, it’s very hard to balance to assets and the drawbacks.

According to me, the risks comes more from the way we dive. And that being true for both OC and CC.


Keep a critical mindset towards your recycler ! 

The recycler is the machine that’s keeping you alive , but , it can also kill you.

It’s particularly true , and the Murphy law won’t disagree with that : “Anything that can go wrong will go wrong”.

In other words, make sure the dive goes fine !

And in order for it to go fine, you need to respect a few important things.

  • The danger with the recycler is to be too trustworthy towards the machine. It is therefore primordial to have a good initial course to know what to do in case some breakdown happen. ( The famous ” what ifs ” )       
  • The machine’s assembly : the different tests and checks that have to be systematically done before each and every dive.
    Therefore, the planification of this dive should never be done too fast. These are automatisms that are to be acquired , plannification and preparation towards the dive. Indeed the importance of often diving with a recycler.
    The error would be to buy a course without buying a recycler, and never diving with a recycler after that.
  • To be very cautious with your gear is a key rule : this is also true with an Open Circuit, but even more  with a Close circuit. If a breakdown happens before the dive, it has to be fixed immediatly, or you have to cancel the dive.
  • Never dive with a failing machine : the entire tests have to be done before the dive, in a calm place, without any disruption.

“Beware of any distractions in those key moments.”


  • Always be aware of the PPO2 :  : This seems pretty obvious, but in fact, it’s not always that easy ! Especially for photographers like myself who always draw their attention towards the  camera’s viewfinder.
    You always have to keep in mind that at any moment the PPO2  can rise or drop and reach critical steps. Becareful to the lifetime of the ceculles that analyse the PPO2, it’s the HUGE drawback of recyclers.
  • Take care our your bail out, verify gazes, regulators, and make sure to have enough quantity to get to the surface while doing your safety bearings. You have to prepare and planify your dive !

Recycler and Rebreather diving

When should you step up to the recycler ?

In France, the legislation requires you to be at least level 3 and Nitrox confirmed, to start a course.

It’s the strict minimum to my mind !

To start thinking about getting into recycler diving you have to :

  1. be perfectly at ease underwater
  2. be passionate about diving, and technique  i am not talking about TEK dives, but of techniques at the proper meaning of this term)
  3. Love your gear, and take care of it
  4. Be disciplined and methodical. If the simple fact of preparing your block is a hastle, don’t even think about the recycler.être parfaitement à l’aise sous l’eau


Diving using a recycler isn’t done randomly

You got it ! To dive with a recycler, you need to be passionate, a very self-aware passionate.

If you are a young underwater photographer,don’t even think about going towards the recycler before perfectly mastering your technique.       

The management of a recycler requires more attention and pratice than an open circuit one.


Conclusion : I am a recycler diver 

It has now been 4 years since I started diving in closed circuit, and there is NO WAY I am going back to an open circuit.

Beside the advantages these kind of machines offer, I have always been attracted to this technology and this technical part of diving.

I enjoy it, and I am very enthousiatic, even at the thought of preparing my machine for a dive !

“It’s a true passion and I think this is the main motivation of diving with a recycler.”

Of course, as a photographer, I have other points of interests while diving in closed circuit.

The approach towards animals is totally different.

Some fish are still very fearful at the sight of divers, but most of the time, they don’t mind, or they are curious and come have a look at you.

I managed to see behaviors at I never saw in open circuit, and that I would have never been the witness otherwise  .

Settle at the bottom of the sandy ground, between two reefs, and in less than 5 minutes you will feel invinsible.

The real reef life will open to you !

The exploration of the 40/50M zone also takes another dimension.

The pressure of time being less strong, we can take more time to sit, watch and enjoy.        

Think  about sharing this article if you found it useful, or if it helped you ! 🙂