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Post by vance on Nov 26, 2020 9:50:38 GMT -8
This is an interesting bit of history from the earliest days of scuba diving. In case anyone doesn't know what this mod is, it was featured in the July 1953 edition of Popular Science. It is the way many early divers got into scuba. It is a how-to article on converting a surplus aircraft oxygen diluter and oxygen tank into scuba equipment. The article is woefully inadequate, lacking in crucial information, and the engineering is flawed. This conversion has issues on many levels, but it can be done, and was by maybe hundreds of people. One company named Seahorse converted surplus diluters and sold them to the public. The premise is to waterproof the cloth diaphragm, remove the cockpit air/oxygen mixing unit, plug the pressure gauge port, add an exhaust system, make up a hose loop, tank pack and harness, and go divin'. There were fatalities. Yikes. You can see the original article on Google Books for free. It's near the back of the issue, around page 160. books.google.com/books?id=Ti0DAAAAMBAJ&printsec=frontcover#v=onepage&q&f=false
Bill T did one a couple years ago and posted his build on VDH. I know some of you smirk knowingly when I say I'm not doing it, but social distancing has given me more time to brood over projects.... And it is a challenge.... And I DO have the diluter just sitting there.... Bill is goading me to try my hand at it.... And it's what I do. We'll see. If I get some ideas that make it different, or better, I just might! I got a good price on a diluter, took it apart, and tossed it all in a box a couple years ago. I vowed I wouldn't do it. POS is made of cast aluminum, has a brass bellows for the first stage (neither of which plays nicely with saltwater), there isn't an exhaust system (since the exhaust air was just dumped into the cockpit), the intake system is convoluted and made to mix (dilute) the oxygen with air, and the diaphragm is 70 years old, not waterproof, and pretty crackly to boot. Why bother? |
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Post by vance on Nov 26, 2020 12:05:20 GMT -8
But I DO have a couple ideas that are an improvement over the original conversion. One is the addition of a standard yoke-type mount to bring the regulator down to a better position. I'm thinking of attaching a brass bodied yoke mount to the back plate of the diluter. The brass body would hold a filter, and be threaded for the yoke nut. An HP tap will be drilled into the body. A tube feed from the tap will direct the HP air to the diluter's HP inlet.
I'm also looking at a straight through second stage to intake horn air passage. I'm wondering if a venturi would work better than a straight through tube.
If I was to do it.
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Post by nikeajax on Nov 26, 2020 12:19:31 GMT -8
And I know you that much: you will do it; good for you! As long as you have a backup reg or at the very least someone who will never be more that three feet from you side at depth; I think it will be a good experiment to play with   JB |
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Post by nikeajax on Nov 26, 2020 16:04:13 GMT -8
Say, I just looked at that: it's wonderfully frightening!  Hmmmm, I wonder if you asked James if he could help you come up with an exhaust cover. My thought there is that you make something that looks like, well, this:  A sprinkler-head that you can put a mushroom valve into... JB |
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Post by SeaRat on Nov 26, 2020 17:28:44 GMT -8
I actually like the following two articles, one on making an underwater camera case out of plywood and the other about snorkeling and showing a full-face snorkel mask.
I would not work on the Bendix oxygen diluter project, as it seems really a bad design. I note that the exhalation hose is normally flooded, with a "flutter valve" a variation of a duckbill) in the exhaust side of the mouthpiece.
John
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Post by vance on Nov 26, 2020 20:33:59 GMT -8
It would have a standard configuration exhaust hoseloop with non-returns and an exhaust valve. I'd use one in or on the bottom box if I can figure out a period correct system.
JB, your photo is not showing on my computer. Is it just me?
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Post by nikeajax on Nov 27, 2020 9:07:46 GMT -8
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Post by vance on Nov 27, 2020 10:16:19 GMT -8
The PS design puts exhaust air back through the intake horn into the air side of the regulator box rather than routing it over the top of the main diaphragm on the water side. The exhaled air has to find its way out through the diluter/mixer opening which is modded to mount a duckbill valve. This design is bad on several levels. The diver will be rebreathing a lot of CO2 b/c the design mixes exhaled air with fresh. It increases exhalation effort due to the convoluted path the exhalation would have to take, and the moisture from the exhalation causes condensation to form inside the regulator. Its one advantage is that it's easy to make it that way. You can see the mixer at the top of the picture, and the mixer air "box". On the left is the intake air horn. The air discharge from the second stage is to the left of the brass IP adjuster in line with the intake horn.  I would follow the path of the OGs who ignored the PopSci design:  Some routed the exhaust into a homemade bottom box in the conventional manner, or simply stuck the exhaust valve on the outside somewhere. I'd cut the dome off the mixer assembly and use the hex headed mount to plug the mixer hole. All of the mixing bits would get tossed. If I was going to do it. |
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Post by vance on Nov 27, 2020 10:57:50 GMT -8
I would also install a tube straight through from the second stage port to the intake horn which would seal off the mixer "box" and direct air right into the horn.  |
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Post by nikeajax on Nov 27, 2020 14:22:30 GMT -8
OK, so... Whotif... you went the HW route and soldered/epoxied a bar across the exhaust chingadera (the part that looks like a car's radiator thermostat would be taken out) and vent the sides to expel the exhaust:  The bar would have a hole in the middle to hold a mushroom valve... I can elaborate a bit more if you want me to but it would have to be through private email as I can just send you images and not have to post them on my Flickr. JB |
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Post by vance on Nov 27, 2020 14:53:29 GMT -8
I just lightened the exposure on the picture a few posts up so it can be seen more clearly. The thermostat looking thingy JB is talking about is the cockpit air inlet (mixer) which allows ambient air to be mixed with the oxygen coming out of the second stage. There's a configuration of brass bits that run from the intake horn to the second stage opening that do the mixing that have been removed and will not be used in the conversion. The cage with a spring inside the mixer box is a clapper valve. (Oddly, it looks just like the ones used as non-returns in Soviet mouthpieces.) That will go, as well. The domed cover has been cut off, mixer components are removed, and the top of the fitting has been machined flat, simply to use the fitting as a plug for the mixer mounting hole. The hole will be sealed with a smaller threaded plug which might double as a mounting point for the exhaust valve assembly, if I don't fit it inside a top box. The PopSci version used this hole for exhaust gases, but it is not a good design as I described above. 
JB's suggestion will work if the exhaust valve is mounted externally, but I really want to get the valve centered on the diaphragm's center. He is probably imagining a similar use for this hole as a mount for the exhaust valve as I am. I know, I know.... Crap. It looks like I'm working on this. It's been waking me up in the wee hours to consider what kind of venturi I could make, and how to make a bottom box with an integrated intake horn. |
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Post by vance on Nov 27, 2020 15:25:22 GMT -8
It's exactly the right size for a bottom box!  Some of these conversions sported bottom boxes like this! I've always wanted to make a regulator out of food cans. Maybe this is one step closer to it! |
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Post by nikeajax on Nov 27, 2020 15:33:19 GMT -8
IF?!?!?!?!?
DA, you foolink no one Komrad... JB
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Post by vance on Nov 27, 2020 15:39:56 GMT -8
You got me JB. Fooling only myself...
Can't help obsessing over this kinda thing. But what's the harm? Just one more bit for my heirs to have to unload. I'm not ever diving it outside of a lake or pool.
If that.
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Post by SeaRat on Nov 27, 2020 15:42:59 GMT -8
I just lightened the exposure on the picture a few posts up so it can be seen more clearly. The radiator looking thingy JB is talking about is the cockpit air inlet (mixer) which allows air to be mixed with the oxygen coming out of the second stage. There's a configuration of brass bits that run from the intake horn to the second stage opening that do the mixing that have been removed and will not be used in the conversion. The cage with a spring inside the mixer box is a clapper valve. (Oddly, it looks just like the ones used as non-returns in Soviet mouthpieces.) That will go, as well. The domed cover has been cut off, mixer components are removed, and the top of the fitting has been machined flat, simply to use the fitting as a plug for the mixer mounting hole. The hole will be sealed with a smaller threaded plug which might double as a mounting point for the exhaust valve assembly, if I don't fit it inside a top box. The PopSci version used this hole for exhaust gases, but it is not a good design as I described above.
I know, it looks like I'm working on this. Phil, I think part of the problem is that this "regulator" was not designed as a demand valve, but rather as a continuous feed valve to mix outside air with oxygen from the cylinder so pilots could function above 10,000 feet altitude. It was also meant to be used with a half-face mask (covering the mouth and nose), with continuous feed rather than demand feed. As such, in trying to convert it to a scuba demand system, the entire unit has to be redesigned in order to give the diver the required amount of air, at a breathing resistance that allows the diver to physiologically function. Because of these limitations, it has been recognized as a potentially hazardous modification (as you've recognized by noting that people have died trying to actually use this modification). So while this is an interesting intelectual exercise, please keep in mind the extreme limitations of this redesign and ensure your safety in any actual tests. John |
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