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KISSing the Dolphin Next
KISS = Keep It Simple StupidBlack Text October 2003
Dolphin = Drager Dolphin SCRBlue Text December 2003
Convert the Drager Dolphin SCR to CCR using a KISS valve.
This is an ongoing project. I am currently was diving the Dolphin in stock SCR mode to gain experience and rebreather confidence.
I am in no immediate hurry to convert the Dolphin but I do enjoy doing the research and discussng the options and my choices.
The reason I chose to convert the Drager Dolphin to CCR instead of homebuild the complete unit was that I believe that making it from scratch is more expensive than buying a second hand CCR production unit and that I don't have sufficient friends or family with the appropriate workshop equipment to make the neccessary bits.
I have been loaned a friends homebuilt unit that is a manual addition CCR. After studying this, production units and studying other units via the internet I realised that there would be alot of proto-typing and testing required to make a homebuilt, with my changes, from scratch.
At this point in time I believe that the Dolphin has enough of the core elements, in the configuration I like, that modifying it makes sense.
More than a few people have displayed their SCR Dolphin to CCR conversion on the internet. These people all have different reasons for converting.
The only portions of my dolphin that will not be standard production items will be the rebreather frame which I have had fabricated and the P port plug for the O2 sensor. This is to carry two steel tanks in a vertical fashion which the original Dolphin case was poorly designed to do.
A kiss valve (as apposed to KISS) is a constant mass flow valve, it can be a needle valve or constant orifice design.
In this application it allows for the constant flow of O2 (oxygen) into the breathing loop at a set rate.
This rate is usually set at just under your usual diving O2 metabolic rate. This O2 metabolism will vary depending on your fitness, your activity level, your anxiety level and a few other smaller contributors.
I have come across several kiss valves.
One type is a variable needle valve designed by Kerry McKenzie. This allows for adjustment to the flow rate before, during and after the dive while in the field without tools.
Another type is a set orifice designed and manufactured by Gordon Smith for the KISS rebreather. This is the essence of KISS with a set orifice and by-pass button. The flow rate is set by adjusting the IP (Intermediate Presure) of the first stage regulator.
I have also seen several other kiss valves based on both of these principles.
The KISS valve is a key element in my conversion from SCR to CCR, but not the only way of achieving the CCR goal.
A manual O2 addition valve is the most simple and straight forward method of O2 addtion, I guess this is really the true kiss principle. The manual addition valve means that more frequent O2 additons are required to maintain a specific set point, which adds to the task loading of the dive.
A computer controlled solenoid could be added that would allow for the appropriate additions of O2. The Hammer Head systems that are currently available for the Inspiration and KISS CCR rebreathers is also available as parts for homebuilt systems. The benifit of this system is that you solve three tasks at once.
O2 addition, O2 monitoring and inline decompression monitoring. Three O2 sensors are installed in the inhalation counter lung and connected to the Hammer Head Computer and O2 display which displays your PPO2 and tracks your deco obligation. An O2 solenoid is installed into either the exhalation counter lung or the entry into the scrubber. This O2 solenoid is controlled by the Hammer Head computer to maintain a set point PPO2.
Once you have decided on your method of O2 addition you need a place to actually add the O2. This can be via one of the jets in the Dolphin dosing head, or via an alternate plug in the dolphin dosing head or via a shrader valve in a P Port in the Inhalation/Exhalation counter lung or through a schrader valve at the scrubber entry. There are numerous methods for O2 addition.
Points to keep in mind:
O2 is best added in the exhalation portion of the system to allow for gas mixing. Lots of small additions rather than a few large ones will help keep O2 spiking to a minimum and help maintain a more even set point which helps with O2 deco tracking.
With all constant mass flow forms of O2 addition it is preferable to use a non-depth compensating first stage to deliver a set IP to the valve (orifice or needle). Some first stages are more easily converted than others to be non-depth compensating. N.B. The inspiration and the SCR Azimuth both use normal (depth compensating) regulators for their O2 regulators. These systems have been disgned to use the increasing IP of a normal regulator.
Diluent (the gas that dilutes the oxygen) should be added to the inhalation side of the system. Diluent is not added much during a normal dive, generally during decent or during flushing. Diluent can be added via the demand valve on the dolphin dosing head. A consideration is that the demand valve on the dolphin dosing head is designed to receive an IP of 16.7 bar which is much higher than most first stage regs. What that means is that if you use a normal first stage reg for Diluent addition through the Dolphin dosage demand valve you will need to either ramp up the IP of the first stage or change the spring in the demand valve to accomodate the reduced IP.
From my research and from what other people had told me I thought I would need to alter the IP of a normal regulator or change the Drager ADV spring to a US Divers Conshelf SE spring, but after 3 water trials I think the standard spring with a regulator with an IP of 8 bar is going to be fine. My depth has been limited to 11m so far but functioning has been fine to date.
At this stage I have not decided on what brand or model of first stage regulators I will be using for the O2 and Diluent.
I have chosen an Apeks DST4 with Gordon Smiths blanking plug for my oxygen and a Sherwood Brut regulator for my diluent regulator. The Apeks was O2 cleaned and the IP adjusted to 12 Bar for a flow rate of .8L/M. No alterations were made to the Sherwood regulator.
We now have O2 addition (valve, placement and delivery).
We also have Diluent addition (valve, placement and delivery).
It is now time to discuss tanks and gas volumes.
The Inspiration CCR's are desinged for use with the Faber 3l steel tanks that reside inside the yellow box casing. 3 Litres of 230 bar O2 in a CCR is alot of O2, 3 Litres of Diluent in a CCR is a fair bit of diluent.
I have seen the KISS rebreathers using the Aluminium 2.7L tanks for both O2 and diluent which is only just smaller than the above mentioned steel tanks.
Both of these tanks are small and quite light which makes the RB alot easier to handle.
Once consideration is that of how you get high presure O2 for your small tanks. eg.
230 bar 3L = 690L 230 bar 2.7L = 621L
185 bar 3L = 555L 185 bar 2.7L = 500L
100 bar 3L = 300L 100 bar 2.7L = 270L
50 bar 3L = 150L 50 bar 2.7L = 135L
185 bar 7L = 1295L 185 bar 5L = 925L
50 bar 7L = 350L 50 bar 5L = 250L
as you can see that while the larger tanks are bigger and heavier they allow you to continue diving with a much lower presure of O2.
With this in mind I have decided to use Faber 5L steel tanks for both O2 and Diluent. They are the same diameter as the Faber 7L's and my connection method will allow me to use the Faber 3L, the Aluminium 2.7L and the Drager 4 or 5L steel tanks. Versatility.
After using the Drager and Faber 5L tanks on the unit in SCR mode for a while I have decided to go with the Faber 3l steel tanks. These tanks are just longer than the Faber 5l's and 2/3rds as wide. It makes the unit lighter, narrower and easier to handle. I have an Oxygen fill whip and cascade system at home now to allow filling of the Oxygen between dive trips. The diluent I still need to get from a Nitrox clean source but with a personal filter that can be anywhere.
My original Dolphin also came with a Uwatec Oxy2 PPO2 display and wireless sending unit. I have since bought a Uwatec Air Z O2 dive computer which receives and dsiplays the PPo2 from the Oxy2.
The benfit of this unit is that it has two O2 sensors in the Oxy2 unit and that the Air Z O2 not only displays the loop's PPO2 but calculates my dive profile using this information.
I will also be adding via a P Port connector a seperate O2 sensor connected to a display. This will allow for checking the Oxy2 as well as checking the system from a different loop location.
The Oxy2 and Air Z O2 is working out just great. I have since learned that each sensor of the Oxy2 has two cathodes. What this means is that each sensor has redundency built in. If one cathode breaks the Oxy2 unit looks to the other cathode circuit for information. The Oxy2 also has a voting logic between the four cathode circuits to see if things are operating as they should.
The Uwatec Air Z O2 is not really designed for cutting edge decompression calculations. Certainly for the next six months or so I will be diving the unit to recreation/NDL limits. On top of this I will be ascending at my usual slow pace with the brain calculated deeper stops along the way.
I have bought from Richard Harris his Munro 3panel PPO2 display to attach to the sensor housed in my P port adapter. My adapter will house only one sensor but Dave Sutton has promised me some photos of a P port adapter with a hinged base to allow several sensors to be installed inside the Drager inhalation lung without holding the lung open.
If I decide to only use one extra sensor then I will either make the display and try to house and waterproof it or I will kindly ask Gordon Smith for one of his displays.
Eventually I would like to replace the Oxy2 and Air Z O2 with either a VR3 or a Hammer Head display/computer (not for the controller portion - yet).
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