My OAK Rebreather - Introduction

Sven Becker

Sven Becker

Member
The name OAK.

Seems perhaps to be a cocky name... Thats good! Probably this forum will wake up!!!
But my interpretation is "only one ex. of this kind".
I built it for myself to use. I have no intention at all to earn money on my sport - just enjoy it.
So if you find any useful ideas - just pick them up.

Background.

Since 2004 I have really enjoyed diving my KISS Classic 1200 hours.
2018 I decided to build a rebreather close to the KISS brand ideas and adding own ideas matured
during 14 years.
Since Jan 2019 I have been diving my OAK rebreather. 14 months - 130 hours - max depth 75m so far.

Parts and suppliers.

Me
My native tools are chainsaw, axe and som other things…
Only the 2 backbones behind the canisters has been produced by myself.
TecMe.de Martin Tolksdorf
All details you cannot identify in my pics and film has been produced by Martin!!!
Just check his home page.

KISS
The complete loop is ”shared” with my KISS Classic.

Shearwater (what else?)
Petrel 2 reading 3 O2 sensors traditionally placed at the inhale side.
Reacts late and slow on gas addition.
NERD reading 2 O2 sensors and 1 CO2 sensor in the counterlung between the 2 canisters.
The sensors are placed 20 mm from the O2 and DIL inlets and reacts rapidly on minimum gas puffs.
Is used to verify DIL gas choice and check for current limited sensors.
The computers are totally independent using their own sensors. No resistor net needed!
Can switch a computer cable using a wrench.

Hollis
I use a SMS75 as platform. (also currently rebuilding my KISS C on a new SMS75)

Narked@90
Omniswivel and Swagelok gas management parts
Miflex hoses (because they provide almost any length)
A few self made hoses with special lengths

GolemGear
Shrink BOV

https://www.dynament.com/products/gas-sensors/premier-non-ex-sensors/
CO2 sensor
order spec:
Premier CO2 sensor
MSH2-LP/CO2/NC/5/V/P/F
0 - 5% Volume CO2 = out 0.1V to 2.0V
Rising V while increasing gas level
Manual calibration using Minus, RX, TX
Normal Temp range
comm speed normal (will not be used)
over range value 200% (default) of full scale value

I recalibrated this sensor to 0-2%
I may buy another initially calibrated to this value.
Also the 1 minute startup value can be choosen.
I may order that next time….
It concerns easier adaption CO2 sensor/Shearwater computer



My own extra features/thoughts that ”forced” me to make my own rebreather.

Straight loop
No vicious o-ring of death. I only use honest o-rings. Either they leak water into the loop or
gas into the water - easy to detect.
(The flapper valves may be seen as vicious - will replace them often)

double canister, single intermediate CL.
At each single moment, the WOB is only affected by half of the sorb.
CO2 can be measured after the exhale canister. When the CO2 rises, the (inhale canister)
sorb spare time is nearly 2 hours.
As a side effect, the sorb is efficiently used since only the burned sorb is dumped.

Easy to handle water trap/dump capabilities
Look at the Water/Saliva Disposer in the film. Used it 1000+ hours. Also used on two more RBs.
Look at the exhale canister/OPV water dump capability in the film.

Inhale hose water trap
The inhale hose female p-port is longer than normal and sticks into the sensor lid towards the center.
If in head down position, small amounts of water in the inhale canister cannot pass into the inhale hose.

Gas check before use after switching gas.
"Puff and read”

As clean back as possible - As light rebr. as possible - low back profile, about +10cm
All tanks sidemounted

Going SCR
All DIL tanks possible to use to feed the needle valve.

Truly independent computers.
No sensors sharing.

Counterlung balancing weight.
In near horizontal position (5 degr.), the CL pressure is completely neutral. When slowly filled, the gas
is first concentrated in the lower part.
In vertical position, the weight doesn't affect the CL. The gas is filled from the top part.

Hope this leads to a informative discussion. Perhaps I even modify my precious…..

”I never make mistakes. Once I thought I did but I was wrong”

Regards
Sven Becker

The youtube film:
https://youtu.be/EvLVwj76D3U
 
Last edited:
seems a little overly complicated? why not put the sensors into the heads and limit egress points into the MSR bag lungs?

chest has alot of clutter - can you keep track of the different MAVs and add areas?
 
haaginheimer said:
seems a little overly complicated? why not put the sensors into the heads and limit egress points into the MSR bag lungs?

chest has alot of clutter - can you keep track of the different MAVs and add areas?
Click to expand...

Hello Haaginheimer,
The authorities i Sweden has informed that 70+ people should seek isolation as much as possible to avoid spreading/getting that nasty virus,
so I have informed my wife that I will seek isolation on our local dive sites in lake Vättern at a higher frequency this spring...
But now I’m back again..

I will answer your first question later.

You: chest has alot of clutter - can you keep track of the different MAVs and add areas?

The short answer is: Yes it is easy and natural.

I see my chest as the cockpit of my rebreather.
All important devices and connections are easy to reach and handle with both hands.
Even my eyes can be used.

Confession: (blushing)
The valves of tank 3 and 4 are hanging in microbungies near the lower d-rings.
The QC6 manifolds may get caught in the microbungies and next gas switch (if any) may be hard to accomplish.
So free movement of the manifolds must be checked after tank 3 and 4 are installed.

In the film I dive SCR using an 80cuf 50/0 and an 80 cuf 21/0. Valves are hanging in the SMS75 bungies.
I switch hand holding my scooter. Lock at the side not blocked by my big warm mittens.
Also check how natural i add oxygen and dump saliva. Dil is not added because I am ascending.

The film from the cockpit:

Regards
Sven Becker
 
Last edited:
haaginheimer said:
seems a little overly complicated? why not put the sensors into the heads and limit egress points into the MSR bag lungs?
Click to expand...

Hello Haaginheimer,
A lot of my efforts trying to add extra functionality versus "std rebreathers" are put on the counterlung.
Yes there are many egress points into the CL. So i will try to explain the added values that goes with the territory..
The answer to your suggestion to put all sensors in the heads is:
It is impossible.
The sensors (see 4 below) had then to be put on the bottom of the inhale canister to make it possible to measure between the canisters.


MSR Counterlung.jpg

Brief explanation of the 5 CL egress points
The 4 visible devices are placed on a vertical line. On the inside they form an anti-collapse tunnel.

1:The OPV (invisible) is placed at bottom,left side of the CL. This the natural water draining point.

2:Exhale p-port. Placed low to retrieve a nearly self-draining exhale canister.

3:Inhale p-port. Placed as high as possible to
a: not get water ingress from the CL,
b: be ”on top" of the CL (horizontal position).
The balancing weight with a top hinge enables for the active CL room to be in the lower half
and keep the CL neutral balanced.
(I could have used a T-piece and just use 1 p-port ignoring benefits a and b.)

4:The sensor cap holding 2 O2 sensors and 1 CO2 sensor.
The position inside the CL is essential. When checking as below, the CL is emptied by inhaling.
The gas injected to be evaluated is not diluted by residual gas.

These sensors are (normally) connected to the N.E.R.D.
Using a Shearwater to display CO2 was a lucky decision.
The logging of CO2 is giving me really important knowledge.
Has any rebreather on the market CO2 logging capabilities?

The position 20mm away from the O2 and DIL inlet gives unique control possibilities.

a: Current limitation check: O2 MAV can, at any depth puff a very small amount of O2 giving a 2.5 PPO2 reaction.
Petrel2, reading 3 sensors traditionally placed in the inhale canister head, cannot detect that spike.

b: DIL check: After changing DIL I always fill about 1 L to check if the choice is suitable.

5: O2 and DIL inlet. Uses the MSR standard inlet. O2 needle valve and DIL MAV are connected here.



Better water evacuation than many rebreathers.

Given a nearly horizontal position, to evacuate water from the right (exhale) canister,
lean slightly to the left, fill the counterlung by exhaling - hold breath and press the DIL MAV.
Capacity (I guess) 1L/3 seconds. See film below.

Example:
By accident you add 1-2 L water through the BOV.
Do as above a couple of times until the gurgling sound at the bottom of the exhale canister is gone.
The dry inhale canister guaranties the absence of CO2 inhaled.

This test is still to be performed. I will do it before it is time to switch O2 sensors ….
It will be interesting to check the CO2 logging. Probably the wet exhale canister will continue scrubbing
during the rest of the dive ….

Film: Dumping water
 
Last edited:
DeepUnderground said:
How long roughly until you detect co2 between the scrubbers?
Click to expand...

Hello DeepUnderground
Finally here is the answer.

I have tested different loads of 797 from 2 x 1.1kg to 2 x 1.4 kg aiming at optimal load ( reaching the normal limit 0.5 kPa at last dive and then refill canister after the dive.)
At that point there is still fresh 797 in the inhale canister (spare tank) that will last nearly the same time as the exhale canister.
Below I have tested 2 x 1.3 kg SofNoLime 797 diving about 3 hours before reloading 1.3kg.

Regards
Sven Becker


How the CO2 is presented during the dive:

CO2 on Petrel2.jpg

CO2 dive1.jpg

CO2 dive2.jpg

CO2 dive3.jpg

CO2 dive1 next cycle.jpg
 
Sven Becker said:
Hello Haaginheimer,
A lot of my efforts trying to add extra functionality versus "std rebreathers" are put on the counterlung.
Yes there are many egress points into the CL. So i will try to explain the added values that goes with the territory..
The answer to your suggestion to put all sensors in the heads is:
It is impossible.
The sensors (see 4 below) had then to be put on the bottom of the inhale canister to make it possible to measure between the canisters.


View attachment 10396

Brief explanation of the 5 CL egress points
The 4 visible devices are placed on a vertical line. On the inside they form an anti-collapse tunnel.

1:The OPV (invisible) is placed at bottom,left side of the CL. This the natural water draining point.

2:Exhale p-port. Placed low to retrieve a nearly self-draining exhale canister.

3:Inhale p-port. Placed as high as possible to
a: not get water ingress from the CL,
b: be ”on top" of the CL (horizontal position).
The balancing weight with a top hinge enables for the active CL room to be in the lower half
and keep the CL neutral balanced.
(I could have used a T-piece and just use 1 p-port ignoring benefits a and b.)

4:The sensor cap holding 2 O2 sensors and 1 CO2 sensor.
The position inside the CL is essential. When checking as below, the CL is emptied by inhaling.
The gas injected to be evaluated is not diluted by residual gas.

These sensors are (normally) connected to the N.E.R.D.
Using a Shearwater to display CO2 was a lucky decision.
The logging of CO2 is giving me really important knowledge.
Has any rebreather on the market CO2 logging capabilities?

The position 20mm away from the O2 and DIL inlet gives unique control possibilities.

a: Current limitation check: O2 MAV can, at any depth puff a very small amount of O2 giving a 2.5 PPO2 reaction.
Petrel2, reading 3 sensors traditionally placed in the inhale canister head, cannot detect that spike.

b: DIL check: After changing DIL I always fill about 1 L to check if the choice is suitable.

5: O2 and DIL inlet. Uses the MSR standard inlet. O2 needle valve and DIL MAV are connected here.



Better water evacuation than many rebreathers.

Given a nearly horizontal position, to evacuate water from the right (exhale) canister,
lean slightly to the left, fill the counterlung by exhaling - hold breath and press the DIL MAV.
Capacity (I guess) 1L/3 seconds. See film below.

Example:
By accident you add 1-2 L water through the BOV.
Do as above a couple of times until the gurgling sound at the bottom of the exhale canister is gone.
The dry inhale canister guaranties the absence of CO2 inhaled.

This test is still to be performed. I will do it before it is time to switch O2 sensors ….
It will be interesting to check the CO2 logging. Probably the wet exhale canister will continue scrubbing
during the rest of the dive ….

Film: Dumping water
Click to expand...



Replying myself.

In april 3, a thread started on FB CCR Explorers Discussion Group
"I heard a claim that wet scrubber maintains 95% of its Co2 absorbing capability. Is there any sources on this?"
https://www.facebook.com/groups/ccrexplorers/permalink/3137964976429304/

I have now performed the flooding test above and have interesting graphic to show concerning wet Sorb efficiency.

It is a pity such important discussions are not made on this kind of forums where you can find them forever (hopefully).
(cannot load pictures anymore - probably my quota is exhausted. Workaround= pics as youtube films. Press stop button for long check)
Here is my flood test.

Compare with normal dive
 
I would want a better water trap... but kinda hard to do with that design...
Nice to see another home build.
Getting kinda few now adays
 
Rol diy said:
Like your idea.. and like double scrubbers.. is the weigh necessary for better wob?
Click to expand...

Hello Rol diy
Yes In my case the balancing weight is necessary. With the weight the static lung load SLL is heavily reduced in near horizontal position (during 95% of the divetime).
When vertical, the influence of the weight is minimal and the counterlung balancing point is dynamically moved towards the lung centroid horizontal line. Dynamic SLL!

Placing the counterlung(s) is always a compromise. In your favourite position, the CL should be as near the horizontal line of the lung centroid as possible.
Here is a link to an old paper from 1998 explaining it all.
http://diyrebreathers.com/data/uplo...f-breathing-in-rebreathers-by-jack-kellon.pdf

I have cut pictures from it and tried to explain my construction in the pdf below.
Regards
Sven Becker
 

Attachments

So does it breath better than a kiss classic? Because that's back mount lungs as well....
Your 6liter lung can maybe move away from your body more than a kiss. But the weight help keep it tighter to your body and keeps pressure on it most times... right? So WOB should in theory be better I would think...?
 
Reason for asking... I have a bio pack. And they use a spring in there for positive pressure with a full face mask on land.
And I think I need a stronger spring to help the WOB be better... in horizontal position.... now it will not reduce in a vertical position like yours.
 
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