BIOPAK rebreather conversion

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BIOPAK rebreather conversion

Message non lupar Eric » Juin 29, 2013, 6:38 pm

Trouvé sur le web...

People often ask whether or not it is possible to convert a biopak 30,45,60,or 240 into a underwater diving rebreather

Short answer: YES

They should be asking:

Is it worth it to convert a biopak to underwater use?

Short answer: NO.

Slightly longer answer: MAYBE

First off, you have to ask yourself what you hope to get out of it. Realize this: At present, there is no nationally recognized agency to certify you on this. Someday there may be, but not in your lifetime. This means that no boat or dive shop will have anything to do with you and your rig, no mater how good it is. Even Morgantown (current parts supplier) will not deal with you if you breath a word of what you are up to. You will be on your own.

If you just want to experience rebreather diving, many dive shops have an "intro to rebreathers" that will cost you very little. (comparitively.) Certainly much less than it will cost you to even get your biopak into the pool.

If you wanted to use the biopak as a pure O2 rebreather, and limit yourself to 20 feet, you may find you about break even.

If you were going to make it a fully functional CCR, capable of normal scuba depths, you will spend a lot more money than you would if you just bought a regular rebreather that you could get certified on.

If you can do without the services of a dive shop or charter boat, and if you can get your sodasorb and oxygen fills on your own (and you can, of course, if you are determined to do so.) then the next question is:

How well do you know yourself?

Will you ever finish the project? Most Biopaks you see on Ebay have been there before. And again before that. Be honest with yourself, do you have any cars waiting to be restored? Got space in the trunk for a biopak?

What is your confidence in your skill level? would you pilot a helicopter you built yourself?

How are your diving skills? You should be pretty comfortable with your rebreather skills before you try to build your own.

There are, of course valid reasons to build your own rebreather. At this point in history, it is unfortunately, still possible to build a better rebreather than you can buy. If that is your goal, the biopaks are not the place to start. They have inherent limitations that cannot be fixed.

There are a couple of good reasons to build a rebreather out of a biopak, but cost is not one of them.

Often much is made about the original cost of a new biopak. It is true that they go for four to five thousand dollars each new. Look at the catalog, though, and its not hard to say why. Six dollars for a screw, a few hundred dollars for a rubber diaphragm, it adds up. These are designed to be paid for by taxpayer dollars, the prices would never hold up on the open market. Keep in mind also, that if you get serious about this, you will be throwing out about half the supposed value of the rig in parts that just don't work underwater.

It is also commonly thought that the mask that comes with it can easily be converted to a Divator.

Depends on what you call easy. First, the correct lens will cost you about a hundred dollars. The AGA style masks also do not have nose access, so a nose block is also required. Next, you need the face plate, and regulator, or rebreather adaptor. You are looking at $500-$1,000 to make a functioning underwater mask out of this. So what you get, basically, is an AGA skirt.

Fortunately, most people don't use full face masks, so this is less of a problem. It is not a problem at all if your unit ships with the scott mask instead, as there is no conversion at all for that one.

Lets say you decide to do this anyway (I have done over a dozen, and will likely do more.)

The first step is to decide which model to use. The bp 30 is very uncommon, and has an excrable scrubber, so let's just ignore it altogether.

The BP-45 is a major league diversion from the line, it doesn't come with any of the expected biopak style enhancements, such as a scrubber (used disposables) or regulator (seriously, it uses a capillary tube for pressure reduction). To make things worse, it has even smaller breathing tubes than the other biopaks, and none of the parts are compatible- with anything. I have converted these to diving, but have since decided that there is absolutely no way at all that it can be made worthwhile, except perhaps as a joke.


This is probably the easiest to convert, and the only one that was originally designed for diving. It started out as the CCR-25, a pure oxygen rebreather that also was marketed (unsuccessfully) to the military as the Cobra system.

When it failed that, it was colored orange and sold to firemen, where it did very well. The bp-60 is different in a lot of ways from its predecessor, but not so far that it can't be changed back. probably the worst factor of the bp-60 is that it has the world's worst scrubber. It is so thin that breakthrough is normal, not the exception. This design also wastes a huge amount of sodasorb. The Bp-240 cannister holds less than twice as much, but goes four times longer. Also, there are no ridges in the bp-60 scrubber to limit channeling, and no tension device on the scrubber bed, other than the compression of the foam pad, so settling is almost certain. The scrubbers are interchangable though, so in essence, you can have biopak 240 performance in a bp-60 size, if you are so inclined.

The bp 240, despite its similarities to the ccr-500 and 100, was never meant for diving. It shares more in common with the biopak 60, such as scrubber, scrubber lid, and plumbing. The case is larger, both in length and width. It comes with the larger scrubber, but almost never the mask or tank. The challanges of building a 240 are slightly different than a bp-60, but if you have built one, you can build the other. If you are looking to build a more serious RB, this might be the place to start. Or it might be a total waste of money. (see below.)

Once you have decided which model to start with, consider the vintage.

Normally , the newer ones are better in several respects.

The hoses smell better and are more squash-proof. (older ones always have the squashies.) Newer ones have the push-button add valve. newer ones have movable scrubber connections, which many of the older ones had molded on. The newer ones may also have additional oxygen port connection areas available, though you still have to drill and tap them yourself.

Older ones (square box era) had better regulators. They were dual-tank style, not just limited to oxygen tanks. They had a built-in o-ring, so you don't have to get a bartok or plastic washer.

of course, if you end up not using the reg, this is not a plus.

Ok, lets assume you have selected the bp-60, modern style (rounded top shipping box)

As I see it, there are three basic levels of conversion that you may attempt. Obviously there are endless variations, so I'll ignore them.

Level one:

for those who just want to make it work, no matter how poorly, either couch diving or swimming pool, for whatever reason. They don't care if it all rusts out, or how it performs in real world settings, they just want to join the storied leagues of RB divers in any way possible, no matter how minor.

Get a couple of hose clamps and a 1" pvc fitting with a 3/4" tee. Heat the tee and squash it to fit a scuba mouthpiece. Get a couple of snorkle one-way valves and poke them down the tubes in the appropriate direction, and clamp the Tee on. put fresh sodalime in the scrubber, and a full tank of O2 in. Breathe off of this for at least half an hour just to make sure you have it all down. Have a friend handy. While you are sitting on the couch breathing, take a moment to add things up. You probably paid $100-$200 for the bp-60 carcass, another $100-$150 for the sodasorb, shipping, handling, small parts, oxygen fill, you are most likely $400-$600 into this thing, and its only fit for a pool dive. Take your rescue diver buddy and go in the shallow end of the pool, sit underwater for a while and breathe, then try swimming back and forth for a while. Naturally, you will have done all normal rebreather checks topside first, so there should be no leaks. If there are, of course, terminate the dive by standing up.

When you get out of the pool, look under the scrubber. There will be moisture. Dip you finger in the puddle, if it forms a string, it's your slobber. That's OK. If it doesn't, taste it. If it tastes like chlorine, you have a leak. That is not so good.It may be from your mouthpiece, remember, it has no shut-off capabilities, its just a pipe fitting.

Chances are, at this point, you have concluded that there is a bit of hype in the concept of "easily and cheaply converted" yes, you have actually breathed off of it under water. You survived. It worked. However, in this length of time, you have also noticed that the breathing hoses are exceptionally long. They have to be, to go under your armpit and around to the center section. Somehow, at this point, you realize that more needs to be done to make this thing really divable.

This would bring us to:

Level Two: a divable rig, pure oxygen

I am not going to cover SCR and the biopak, simply because SCR sucks. They require an outsize tank (up to 50 cf are commonly used.) they still make bubbles, they still use more gas with depth, and in fact, can actually use more gas than open circuit, under certain conditions. Add the cost of Nitrox and sodasorb, and you have, well, nothing good. It is certainly easy to do if you want to, just drill a .490 hole in the side of the breathing chamber, and you can fit any Drager orifice you want to. But I said I'm not going there, and I won't. That's just throwing money down a rathole.

So the middle road here is to convert (revert?) the bp-60 to ccr-25 days. You will come out of it with a pure-O2 rebreather, complete with 20 food depth limit. Just about the cheapest way to do this will cost you another few hundred dollars, bringing your total up to over a thousand, which would have bought you a Drager Ray (yes, its a justifiably discontinued piece of poo, but you would at least have a chance to dive it on your vacation to Grand Cayman.) and maybe the training, too. (Ray instructors, if there are any left, must be getting a bit edgy by now.)

But let's press on. First thing to do is strip off all the things that started rusting since your pool episode. all iron goes, all the aluminum, the honker, the suicide valve, and perhaps the orifice, though that is a personal choice. If you are going to use the original regulator (yes, works fine at this depth) you need to change the pressure gauge for a submersible one. Take the reg to a machine shop and have them spot-face the connections so you can use o-ring seal hoses, at least on the HP seat. Decide beforehand whether you want the LP seats converted too, as they generally charge at least 60 bucks an hour (it adds up) Either use an old style hp gauge, or get an adapter to use a new one, because the threads will be the same as LP side threads.

If you have the old turn-style bypass valve, dump it and replace it with a toggle valve or KISS valve. These run 50-500 bucks, depending. If you have the push button style valve, as a suggestion, take it apart, clean it and replace the schrader valve. If you haven't already, also replace the main oxygen addition valve, which is also a tire valve. If the thought of being fed off a shcrader valve bothers you (and it will, the first time it fails to operate under load) then go to morgantown and order the little T-shaped lever. It seems expensive, but it makes this work a lot better, and its definitely less expensive than replacing the main diaphragm. (HUNDREDS of dollars) I say replace because once the little brass insert falls off of it, there is nothing on earth that will make it stick back on (reliably) and so this little later-day mod is definitely worth it, if you hate that oxygen-starved feeling as much as I do.

As long as we are spending the big bucks here, I am going to tell you straight up, you need two things to make this work at all well as an underwater rebreather.

1: get the 240 scrubber. Its a couple hundred bucks, but quite necessary, if you hate that co2-buildup feeling as much as I do. ( you will.) you might not need to get the bp-240 lid, often it is enough to remove the cooling rings and grind off the bolt stubs to make it fit. If not, another couple hundred bucks. You can also stretch the scrubber if you are good at that kind of fabrication, but I certainly wouldn't recommend it, if you aren't 100% with your skills in this area. if you choose that option, count at least 20 bucks, possibly more.

2: Get a dsv. Yes, you can make them, but there is a place in germany that sells them cheap enough that you don't have to kill yourself trying to make one. they are a couple hundred bucks, or you can get one of Gordon Smiths for about six hundred.

3: wings. I know I said 2 things, but did you really think this would fly without some kind of BC? no, it won't. get a nice trans-pac and wings, or something similar. Yes, It may set you back another 500, but on the bright side, you can always take it with you when you graduate from this system.

4: Pony bottle: as with 3: above, you need one anyway, no matter what kind of RB you dive, so it doesn't really count against your total cost. Lest this turn into a Monty Python skit, that really is the last of the major really needed items.

OK, now you could have bought a used dolphin with the amount of money you sunk in this thing, and if your time is worth anything, you would have had a sport KISS before you are done here. So why do we do it? I can't say, really what the attraction is... Oh, yes I can, I get paid for this. What's your excuse? Oh, well, anyway, back to work.

The next thing you want to do is rotate the center section so that the connectors come out the top. Move the lid latch if necessary, also you will have to build up the two bottom center section connection points, because doing it this way puts them in a bad location. Some people have a delrin mounting ring machined instead, this is a great solution, but again, 60 bucks an hour plus delrin, which is not cheap. Nylon is just as good for this application, by the way.

When you do this, you also destroy the warning label, so get another. Yes, it is important. Or get one of Jetsam's, they are pretty much to the point as well. Or you can use my favorite, the one I have inscribed (or scrawled) inside all of my deep-sea helmets:

"Today may be the last day of the rest of your life."

That's mine, but you can use it. Think on this every time you dive. Make sure it never comes true. (on a dive). By coming out the top, you save about four feet of that convoluted hose, which may or may not make a noticible difference in your WOB, depending on how many sit-ups you do every day. Either way, it is a lot more elegant (less dorky) than the under-arm crap. Seriously, you have to wonder how they came up with that.

Most people will change out the original steel bottle for a C-size oxygen bottle. This is about as large as you can get without dismounting the oxygen reg. If you have used the original steel bottle, that works too, if you remove the pressure gauge and plug the hole it leaves.

Consider casting some weights for the inside of the cover, the closer you can get this thing to your back, the easier it will breathe. If you don't like casting, get some really fine lead shot and make an epoxy-lead syntactic goober and paste it in there (AFTER you get all your plumbing finalized.)

This will only achieve about 80% the weight efficiency of cast lead, but its a lot easier to do and you won't get burned.

At this point, you have someting fair, you may be able to replicate a LAR-V dive profile, as far as depth and duration (20 feet, 3-4 hours) good on ya. Believe it or not, this may hold you for quite a while, if you live where there are a lot of great shallow dives. You do not yet need oxygen monitoring, just a pressure gauge.

How much money do you have invested? Best not think about it. A lot, but remember, there are many reasons to build your own RB that cannot be counted in terms of money. I guess.

Level 3:

Free-fall zone. Heart of darkness. You are colonel Kurtz and your methods have become unsound. No messenger is coming up the river after you. That sound is your wife beating on the garage door. Better not let her in.

You have come over to the dark side, and there is no going back. you want to dive normal scuba depths, and maybe, beyond. you definitely need some oxygen monitoring at this point. Be warned, as you cruise the web looking at what others have done: There are some pretty bad ideas out there.

Abandon the one hundred-two hundred dollar zone now. you are in the one-two thousand zone. You can, of course, go to oxycheq and build your own oxygen monitor. Then you have to put it in a waterproof casing (all together now: sixty dollars an hour plus materials) or you can buy it stock, from one thousand-two thousand, depending if you just want monitoring, or an actual computer that calculates oxygen dosage in real time.

Now you also have to add a diluent system, which means another bottle, another spg, another addion device, etc. (it is tempting to use your bailout as diluent, but not always a good idea)

you may also find that you have outgrown your noryl plastic orange box of death, and now want a stainless backplate, with a carbon fiber shell (at this point, it doesn't matter whether you started with a bp60 or 240, there won't be enough original parts left to tell the difference)

to paraphrase mr. Popeil: NOW how much have you paid? well, again, it doesn't matter at this point, you are obviously into this thing for reasons no one but another bp fanatic can understand. You have also run up against some of the dirty little secrets of the biopaks. Small bore hoses are fine for shallow diving, up to normal scuba depths. In fact, they are preferable, if you have rough waters or ride submarines or scooters. However, there really is something to the hose diameter thing when you go deep. It is possible, of course to adapt the hose sizes up, but the connection to the center section will never be larger. In fact, one of them is only half diameter, and though not a real issue, it will cause you to have unclean thoughts about modifying your center section.


at some point, you just have to accept the basic limitations of the device, or give it up. When you get here, stop.
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