Biopak Center section lid and scrubber mod

S. Marc

Hi,

I have been slowly, and I mean really slowly working on modifying two biopak 60's over the past couple of years, (if Patrick Duffy is reading this he is probably laughing, as I purchased one from him 4 years ago, and have been struggling with it ever since ). Only one has been wet, and just as an O2 rig, albeit with sensors and a 3PP02 display and a set of buddy inspiration counterlungs. Don't ask .

I stop, start, give up, drool when looking at new rebreathers coming on the market. And then start again. What can I say, Canada is cold in the winter with not much to do but tinker.

About a year and a half ago, a friend said he could weld an extension to the centre section lid, which meant that I could then fab up a larger scrubber and fit sensors on top of the scrubber like Mark Munroe. I would then have a Biopak with some decent duration, an increased loop volume, that maybe I would trust below 70 feet. So, I took more interest in finishing the conversions.

I had a spare BP 240 lid I got from Patrick, and being eager to finish the project, I parted the centre section lid about an inch from the top. This so called friend of mine then did some checking around and it turns out the lids are made from spun stainless steel, and cannot be welded. Too bad he didn't check before I butchered the lid.

What I am now trying to do, is create an extension to the butchered lid using fibreglass and the bottom 3 inches or so of a home depot bucket as a mould. Pictures to follow if anyone is interested. So far the project seems to be working quite well, and there are a few more coats of cloth and resin to go.

I also bonded two BP 60 scrubbers together using good quality 2 part epoxy (actually Brownells bedding compound that I use to bed rifles - it sticks to just about anything) and am in the process of covering the seam between the two scrubbers with a couple of layers of fibreglass resin to ensure it is a gas tight bond. I think the double scrubber will take between 4 to 5 1/2 lbs of sofnolime. Comparing the double scrubber to pictures of the BP 240 scrubber I have seen on the net, I think the double scrubber is quite a bit larger than that of a 240.

I have done some rather crude calculations and have come up with a loop volume of approximately 9 1/2 to 10 litres with the lid extension, not including the the hoses and DSV. Once the fiberglass has cured, I will be able to measure it more accurately with water.

My question is do you think it is safe to have a fiberglass lid extension bonded to the SS lid in this way? I have heard that LAR 5 scrubbers are made of fiberglass, so I am not to concerned with using fiberglass as the material itself.

I am concerned, that when ascending, the fiberglass extension may part from the SS lid due to increasing pressure, notwithstanding that there is an OPV on the lung. I am considering doing an epoxy layer or 2 for added strength once the fiberglassing is finished to hopefully add some further strength to the graft. The fiberglass extension is bonded to both the inside and outside of the center section lid with about a half inch overlap, and when finished, will have 4 layers of fine mesh fiberglass cloth sandwiched together.

Any thoughts? Do you think this thing will explode apart when I ascend? Gives a whole new meaning to flooding your loop.

Any info you can provide is appreciated.

I may just be able to finish this project in a year or so.

Thanks,

Marc

Genesis

I'd use epoxy instead of general purpose fiberglass resin (polyester) for a number of reasons, not the least of which is the styrene component in polyester resin.

I'd have some concern about the bond between SS and a fiberglass layer. I'd probably bond up a small section of a couple layers of cloth to a piece of the same SS and then see if you can break it apart. You're looking for the glass to fail before the bond does. If so then you're golden.

apitkin

Think about it this way: you can get AGE from a lung overpressure of as little as 80 mmHg (a little over 1.5 psi). You should not be getting anywhere near this kind of overpressure in the loop unless you are ascending holding your breath or with the DSV shut (i.e. bailing out on OC).

So you could regard your epoxy-stainless bond (I have no idea how strong this will be, but plenty of people here do I'm sure) as your lung over-pressurisation protection device

Andy

waynej

Please send me over some pictures of this MOD.
I would like to look it over and give you my two cents on this.
I have worked with many BP60s and a 240.
It would seem as if you are making things harder on your self than you need to and I do question the safety of this, but I will need to get a better understanding of what you are doing as well.
Please fell free to check out my sight at
www.rebreathertech.com if you have not seen it before.

Wayne.
www.rebreathertech.com

waynej

Sorry forgot to include my email.
waynej528@rcn.com

my mail at rebreather tech is not working right now, not sure why , I will have to get Ted to fix it soon. LOL

Wayne.

OxyCheq

Well, at least you are still married.

Patrick

James Appel

I dont understand why you cant get them welded together, someone with a TIG welder should be able to weld stainless steel with no trouble. I dont like the idea myself as to bonding it together with anything other than welding

Scuba_Vixen

Silver brazing may be your answer here.

Working the metal changes the grain structure so that if it's heated enough to weld it, it'll end up cracking later, just behind the weld. ... If you silver braze it, there won't be as much heat, and the joint will have some flex to it allowing for slightly dissimilar expansion/contraction rates between the spun piece and the extension piece.


Darlene

S. Marc

Lids are almost done. Covering the first one with multiple coats of liquid platic at this time, to prevent any chipping if I drop it.

The guy that was supposed to do the welding is a journeyman class B pressure welder, so I just followed his advice not to weld, as he stated that as it was made from spun stainless steel, as soon as you put any heat to it it would start to spatter and would disintegrate. I saw no evidence of this when I parted the lid though.

I do some mig welding at home with a small 110 v 120 amp mig welder, but have never welded stainless so I deferred to him. I still have the parts that I parted, so I may try some test welds on them once I get the right shielding gas and wire.

The lids are just about done, but I have a third lid that is not modified in case I f_ _ _ it up and I will post pics of some of the different stages of modifications when they are totally complete.

I took the advise of Genesis and completed the bonds with Cold Cure Epoxy and multiple layers of cloth and epoxy. The molded extention on both lids is about a 1/4 inch thick, and seems very strong.

If this does not work, I may try and create a whole new lid from a mold. I don't think my wife would let me buy a bigger lathe with enough swing to allow me to machine one from scratch
Marc

S. Marc

Okay,

Here are some pics from about 3 weeks ago. The lids and scrubber have progressed much further, and are much more finished looking. These pics show the lids with only about 2 coats or so of epoxy and cloth, and they look and were pretty rough.

Marc