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Post by SeaRat on Sept 1, 2021 8:33:19 GMT -8
It looks like the hose loop on the Popular Science article would allow a lot of CO2 buildup and rebreathing.
John
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Post by antique diver on Sept 1, 2021 14:18:13 GMT -8
AntiqueDiver chronicles his diluter conversion in a very interesting thread on VDH. His conversion goes deeper into modification than the PopSci conversion, including a homemade silicone diaphragm. I have been meaning to start a thread here on the O2Aviation conversions, but instead of starting over from scratch here's a link to the lengthy previous discussion that Phil referred to:
www.vintagedoublehose.com/forum/viewtopic.php?f=4&t=9782&sid=72f4ca05899953985750d171111393aeI have changed a few details since then, but will be bringing it more up to date here later.
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Post by vance on Sept 1, 2021 16:24:52 GMT -8
It looks like the hose loop on the Popular Science article would allow a lot of CO2 buildup and rebreathing. John Yes, it will. This article is probably responsible for several (many?) deaths due to its inadequacy on so many levels. The regulator conversion does not address some potentially lethal issues like the CO2 rebreathing problem. Another is water intrusion into the case from the exhaust hose, which can cause flooding. Another small issue might be the first stage exploding from pressures over 2K psig. When people who had no understanding of how a regulator works blindly followed a how-to like this, tragedy was inevitable. Where was Mark (ScubaLawyer) in those days? Probably in diapers...
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Post by vance on Sept 2, 2021 7:45:22 GMT -8
Great, thanks for linking to that 11 page thread! And please keep us updated on progress. Hopefully, your thread's little brother here can equal it someday!
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Post by vance on Sept 2, 2021 10:26:10 GMT -8
Now I have to figure out a way to vent the tube so suction on the mouthpiece can deflect the diaphragm, but retain the direct second stage output into the airhorn. I am considering making grooves along the side, or a number of holes drilled around the director tube's jet. I rigged up a temporary tank mount to test the beast. Good news is, it didn't explode at 500 psig. It didn't leak or freeflow, either. Bad news is, it didn't exactly overwhelm me with its output. There are some things that can be done to improve it, hopefully!
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Post by antique diver on Sept 10, 2021 9:31:12 GMT -8
Bendix Oxygen Diluter in use, Wheeler Branch lake, 2018.
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Post by nikeajax on Nov 25, 2021 14:19:04 GMT -8
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Post by antique diver on Nov 25, 2021 21:43:21 GMT -8
Ha... When I saw Gutenberg I thought this was a link to the Bible! Actually not a bad idea before embarking on a dive with the system. I did glean some interesting information about the usual operation and the O 2percentages that were provided at different altitudes. However the components that performed that regulation are removed in the conversion, so this doesn't have an effect on the diver. A more important fact that I was not aware of is that the O 2supply pressure in the aircraft was maximum of about 450 psi. That likely explains the reason I have had a difficult time keeping the HP seat from seeping a little air at 1800 psi. That generally quits leaking after breathing the pressure down a bit. Not sure when that happens since I don't have a gauge attached, but guessing below 1200 psi. I will check that on the test stand with a gauge where I can vary the input psi. Now beginning to think I need a small inline reg to keep the input pressure to reg no higher than 400-500 psi. Thanks for the info JB!
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Post by SeaRat on Nov 25, 2021 22:30:26 GMT -8
Ha... When I saw Gutenberg I thought this was a link to the Bible! Actually not a bad idea before embarking on a dive with the system. I did glean some interesting information about the usual operation and the O 2percentages that were provided at different altitudes. However the components that performed that regulation are removed in the conversion, so this doesn't have an effect on the diver. A more important fact that I was not aware of is that the O 2supply pressure in the aircraft was maximum of about 450 psi. That likely explains the reason I have had a difficult time keeping the HP seat from seeping a little air at 1800 psi. That generally quits leaking after breathing the pressure down a bit. Not sure when that happens since I don't have a gauge attached, but guessing below 1200 psi. I will check that on the test stand with a gauge where I can vary the input psi. Now beginning to think I need a small inline reg to keep the input pressure to reg no higher than 400-500 psi. Thanks for the info JB! Okay, that seems to say to me that you have a downstream valve. Can you check to see? If so, you may need to put a first stage between the regulator and the 1800 psi air supply. John
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Post by antique diver on Nov 26, 2021 5:53:52 GMT -8
....important fact that I was not aware of is that the O 2supply pressure in the aircraft was maximum of about 450 psi. That likely explains the reason I have had a difficult time keeping the HP seat from seeping a little air at 1800 psi. That generally quits leaking after breathing the pressure down a bit. Not sure when that happens since I don't have a gauge attached, but guessing below 1200 psi. I will check that on the test stand with a gauge where I can vary the input psi. Now beginning to think I need a small inline reg to keep the input pressure to reg no higher than 400-500 psi. Thanks for the info JB! Okay, that seems to say to me that you have a downstream valve. Can you check to see? If so, you may need to put a first stage between the regulator and the 1800 psi air supply. John Yes, it is a downstream valve, which easily explains the leak issue at higher pressures than the regulator was designed for. I had mistakenly assumed that the stored aircraft O 2 supply was maybe 1800 psi at start. I hope to test it today to see just how much pressure it will digest. I have a fairly small inline regulator that I can adjust up to around 500 psi. It would fit nicely in the valley beside the tank and backplate.
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Post by nikeajax on Nov 26, 2021 8:42:34 GMT -8
Bill, I'm glad I said something and that it was helpful to you: at first I was just going to let it go JB PS Project Gutenberg has lots of great stuff to download and I pretty much am reading something I've downloaded from their site every night...
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Post by antique diver on Nov 26, 2021 11:40:44 GMT -8
Bill, I'm glad I said something and that it was helpful to you: at first I was just going to let it go JB PS Project Gutenberg has lots of great stuff to download and I pretty much am reading something I've downloaded from their site every night... Please always jump in with ideas that come to mind. Even far-out crazy thoughts from friends often lead me to brainstorm from that idea to something new that works! It's very helpful. I have the Bendix all opened up and discovered two things. One, the HP seat is actually not seating well at any pressure... it's just more noticeable of course at 1800 than at 400. I have wrestled with this crazy seat to many times, and now I'm convinced to try making a new one from scratch. That's probably a full day's worth of work for my slow-moving mind even once I settle on an appropriate material to machine it from. But for now it's secondary to another discovery. Two: This is actually the first time I have taken off the diaphragm since making and installing it about 3 years ago. I now find that the demand lever has only been moving part way before the diaphragm reaches its practical limit. When I push it manually (about 1/4" further than a reasonable inhalation effort can), there is a considerable volume of extra air provided from the second stage. There is approximately 1/4" more lever movement If I revise the diaphragm to a 0.25" taller version I will be able to adjust the lever height by that much more and take advantage of that extra throw. I suspect now that the whole issue of breathing super easy under gentle demand, but absolutely terrible under heavy demand, may be mostly due to my design error of the current diaphragm. That is easily corrected with a new shape. Hoping to have some results to report before Monday.
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Post by SeaRat on Nov 26, 2021 12:56:00 GMT -8
Bill,
That's great to hear. We will enjoy your report on the results. These are the things that keep our brains engaged, and growing.
John
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Post by vance on Nov 26, 2021 17:52:38 GMT -8
I have noticed this problem with a few regulators. You need as much movement as you can get from the lever.
I have back-burnered this project (waaaay back) after a very disappointing result concerning output. I am anxiously awaiting your diaphragm results.
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Post by antique diver on Nov 26, 2021 20:23:32 GMT -8
I took off the back plate for a look at the interior, which includes being able to see the underside of the diaphragm. While pressing on the outside of diaphragm and watching it flex it became obvious that the large inside plate (came off original diaphragm) was limiting the amount of flex, and thus the travel range of the demand lever. I had included it on my version of diaphragm because I figured there was a good reason for it, but now it seemed like a little improvement was in order, so out came the diaphragm. In the first photo you can see the diaphragm with original plate in place, and next to it a smaller plate that I would replace it with. I have finger on the demand lever, which attaches to the diaphragm. Second photo shows the new plate in place as I reinstall. The diaphragm is held in place in groove of the housing with a tight-fitting oring. There was a remarkable change in the breathing performance since the demand lever has increased travel that is unimpeded by the lack of flex in diaphragm. One very minor glitch is that as the diaphragm moves deeper than before, the plate touches the edge of in internal body projection, just slightly limiting the travel by about 1/16". Net gain in travel was about 3/16" and I'm not really sure that another 16th is even needed. I still need to address the hp seat leak after finding that it seeps slightly even at 450 psi inlet. Another day... happy for now.
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