Mina MK I MOD I Rebreather

jeib09

MINA MK I MOD I DUAL PURPOSE REBREATHER

What follows here is a lengthly description of a new type of rebreather that is being dove and tested here in California. I tend to be a bit long-winded so now is the time for you to go get that cold beer or that glass of wine and when you are back I will do my best to make it worth your while to read this post...........You're back? OK here we go.

This rebreather is unique in several ways but it is principally different from other units in that the scrubber was designed to be inserted INSIDE the counter lung and is accessed via a drysuit zipper. The reasons why it was done this way will be described below.

WHY WAS THE THING BUILT?

This rebreather was designed for divers wishing to dive to a maximum depth of 130 FSW for up to one and a half hours at a time and who want the minimal of equipment but still want to be safe doing it. It was also designed for divers who would like a pure oxygen rig for diving in the shallows. It has been dove in this mode several times to date. It will soon be a mixed gas manually controlled unit for going deeper than 21 fsw; I am waiting for the money to buy the electronics and the CMF valve. It has not been dove past 21 feet as of yet. Lastly, it may be an excellent bailout rebreather because it is so small and lightweight and can be used with almost any BC/harness that is available on the market today, or yesterday.

The MINA can fill the above roles quickly and easily because it was designed to be versatile and modular requiring no tools to change from one type to the other-just push buttons and add or remove the equipment. It is very robust with the lung being fully inclosed in a forged aluminum case. It is simple, breathes well, and every part that went into its construction was chosen because it was readily available and inexpensive. The MINA is practical too, because the scrubber medium can be changed out in record time, securely, without tools. The project took one and a half years from inception to its current form and cost me approximately $1,200 to complete, not including the BC.

My buddies and I like to dive but we are also very intrigued by the technical side that rebreather diving offers and weve spent hours debating what rebreathers, both past and present, are the best and why we feel so. What is the best rebreather? In my mind, its the one that serves your needs the closest and allows you to dive where you want to dive, safely.

I enjoy diving pure oxygen rebreathers down to 1.6 ATM because there is so much to see in the shallow depths along the coasts. Sea life flourishes in the sunlight that penetrates to 20 feet and there is a never ending shoreline to explore in every ocean and lake. Also, I never find myself too far from dry land and this adds to the safety of this type of diving. However, being a diver of some 24 years I also know that I have a desire to go deeper on a regular basis, too. A rebreather that can perform double duty here is what I would like. Small size and low weight are important because we tend to walk long distances along the shore to enter the water. Give me a light and compact rebreather any day over a heavy and bulky one. A robust rebreather is important for me because I dive in shore break conditions and also because Ive found that the garage monster has an appetite for my diving gear as does the trunk monster. Price is always a concern for me even though I hold down two jobs here in the good old (expensive) O.C.

I have owned and dove several military units in my time and I like them, especially the front-mounts. But heaven help you if you break something and need the part replaced with an original. Parts availability is important to me. Being able to change the scrubber medium easily and quickly was important to me. So basically, when I announced to my friends that I was going to try and build something better they called me out and said talk is cheap. They wanted to see the finished product. The MINA is my all-out effort to produce a rebreather that hits on all the points mentioned above.

The MINA is a front-mount type because that is the kind I have come to enjoy best. Even though front-mounts clutter the front of you they still have their advantages: The hoses can be shorter reducing unwanted buoyancy. For some divers the breathing characteristics are more suitable to their tastes in the sense that the inhale is easier than the exhale. It is generally easier to access the components of the rebreather under water and you can sometimes see what is going on if something isn't right. For example, with the Mina, I can easily press the automatic diluent-add button, turn the diluent on or off, turn the oxygen on or off, add O2, and I know if the lung or any of the components attached to it are allowing gas to escape into the water because I can see the bubbles going by my mask. These features are present in some of the rebreathers out there but in my opinion they are easier to manipulate/see with the front-mount type.

The disadvantages are that some divers ears may bother them because of the pressure differential between the eustachian tubes and the lung. It can be more difficult to get into a boat from the water without a ladder unless you remove the rebreather. Clamoring up onto rocks to get out of surf can be harder and, as was mentioned, you've got equipment on the front of you when you may wish to be uncluttered there. Lastly, if the rebreather is too heavy it can really reek havoc on your neck if you have to walk long distances along the shore to your entry/exit spot. I addressed this problem by mounting the bottles/valves/first stages on my back.

For those of you still unconvinced the Mina MK II back mount rebreather is being developed as we speak. The MK II will be larger with a 16" diameter case whereas the MK I front mount, discussed here, utilizes a 12" diameter case. The MK II will have a larger scrubber and therefore longer duration. Otherwise, the two types will be virtually the same.

WHY IS THE SCRUBBER INSIDE THE LUNG?

I went home and started spending hours drawing countless loop designs in an effort to try and make a loop that was more compact than what was already available without sacrificing good, low WOB characteristics. I tried keeping in mind that every piece I drew had to be readily available at Lowes, Home Depot, the local hardware store or from the diving equipment manufacturers. I put the scrubber on the back, front, sides, top and bottom. I put the lung on the back, top, sides and bottom. I tried to eliminate the hoses. I tried to shorten the hoses. I drew square lungs, round scrubbers. I drew round scrubbers and square lungs. I tried to eliminate the 2nd stages. I tried to combine the second stages. I tried to make sure that whatever I drew would somehow be compatible with buoyancy compensators that are readily available. On and on it went for three months until one day it dawned on me, like a bolt of lightning: put the scrubber inside the lung and the loop will be more compact. Put the scrubber inside the lung and it will operate as efficiently as possible, due to its being insulated completely from the water. Put the scrubber INSIDE the lung and the scrubber will not need to be built watertight. In fact, the scrubber could be one of the simplest types ever made, open on one end, which would make it lighter and cheaper and easier to build. Put the scrubber inside the lung and accomplish several of the design criteria in one fell swoop.

THE PARTICULARS

My Wife says get down to it already. A dry suit zipper is used to access the scrubber. Although expensive, the zipper has proven to be most practical because it is easy to operate and does not leak. Drager hoses and DSV were used as well as a Drager dosage unit. Both of these are from the Ray. The hoses were cut to make them shorter and the elbows were also used. In pure O2 mode, the dosage unit supplies 100% oxygen through a 50 % orifice that has had the little hole filled. This has turned the dosage unit into nothing more than a demand second stage. In mixed gas mode the dosage unit will supply the diluent in the same manner. Currently three p-ports are being used (inhale/exhale hoses, dosage unit). The over pressure valve is from a dry suit. The bubble diffuser was crafted from a 3" PVC pipe cap and contains some of my blood, sweat and tears. Foam is used to diffuse the bubbles. When diving from the shore we sometimes do out-and-back trips where we find ourselves on the ascent leg for half the trip. Brass hardware was used everywhere when bolts and nuts were needed. The counter lung was manufactured for me by Jay Harding (jmhardingjr). It is made of good quality material and is therfore tough. The seams are bulletproof. He glued it and seamed it with heat. It has a 5" gusset which houses the p-ports, zipper, and OPV. He did a great job and I recommend his services to anyone needing a custom lung. He cares as much about the success of this project as I do. We've become friends. The case was once a cooking pot made by IMUSA. The clamps that hold the two peices of the case together securely took forever and a day to locate and are from Southco. They are good people who donated them to my project so that it could be completed and they even expedited them. The grey neck and waist straps came from a Russian IDA 71. All machining was done at home using a dremel tool, sandpaper, files, drill, rivet gun and the MK I MOD I arm.

THE SCRUBBER

The scrubber is made of four inch diameter PVC pipe and the screens are the drainage ones made for that type of pipe. Inside the lung is a four inch to three inch coupler and attached to the coupler is a rubber cap that the exhale hose p-port is mounted to. The scrubber bed is compacted with a brass rod and wing-nut to prevent channeling. Porex screens are being experimented with to keep dust out of the lung. The scrubber is unique in that the main unit, which I call the module, is the only part that is removed from the lung when changing the lime. The procedure is very easy and quick. You can reeinsert the module the opposite way around if you so desire as both ends are the same and fit into the coupler. Or, you may choose to extend the module part-way out of the lung and change it that way if you would like. The scrubber is secure inside while diving and does not wobble around. Not including the work, the scrubber for the MINA can be built for $20.00 so making more than one for quick change-outs is possible.

ALMOST THE END

I hope that you have enjoyed reading this post and I hope it was worth your time. I would like to thank everyone who has posted interesting information on this wonderful site. I thank you because I probably used it to get my project this far. Posting all this is my way of saying thanks. I have particularly enjoyed posts by Dave Sutton, customworks, JAAP, Paul with the REVO, and there are just too many more to list. I would like to thank my good friends, in no particular order: Thom Susko (seabass) and Dave Zebell (dz3866). Without their help this project would not have been possible.

I welcome your comments, both good and bad. I will try to get back to you. If you all would like I will keep you informed of the progress that is being made as major stuff gets finished. If you would like to build a MINA I would be happy to help you. If you would like me to build parts of one for you or the whole thing I can but I have to be compensated for my time as I work other jobs. If you would like to see the MINA and perhaps dive it I am planning on going to the DEMA show this year and will be bringing it along. Let me know if you will be attending and we can meet up. Dont stop working on those projects! I am going to be sad when mine are done! The End of the beginning...

P.S. to see more photos go to Mina MK I photos in the homebuilders forum

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caveseeker7

For most part I'm not all that much into home builds but this one looks very, very well made.
Congratulations, and safe dives.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

grandizer52

Bro that thing rox...great design...i want to try it
laytah
steve

SINUS

Absolutely well engineered piece of homebrewed chest mounted Rebreather rig you got there - very compact and looking good !

Nice work jeib09 ! Thanks for posting the piccies.

cheers

Wei lan

__________________
"Silence Is Always Beautiful"

Mikel-Deko

Woahhhh
Great job.
Very nice desing and very intuitive solutions for some promblems.
Keep on working and we will be very happy with some more pictures (underwater).
Best
Mikel

Dave Sutton

Receives the coveted "Diver Dave's Seal of Approval".

And Boris is happy that it uses Russian IDA-71 straps....

Dave

__________________
"Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com

dz3866

hey Jay, glad to see you have the unit posted now, to everyone here I speak from someone on the sidelines watching this project from the start, Jay spent a lot of time in the think tank on this one and it shows, nice work. BTW when do I get a turn on the unit.

jmhardingjr

Success!! I've always though that this unit looked sweet even before it had a counterlung. I'm glad I had a chance to contribute. Nice job, Bro.

Cheers,

Jay

__________________


". . . the sea's in my veins, my tradition remains, I'm just glad I don't live in a trailer . . ."

caveseeker7

Actually, you may want to submit some pics (incl. UW) to the Crestline Experimental Diving Unit.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

SeaBass

Jase,

Certianly has come a long way from the "Pot Belly".

Now can we quit talking about it and go diving on our new inflatable!

--SB