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Post by SeaRat on Mar 9, 2017 9:40:19 GMT -8
Vance, I'm very happy that you are doing these experiments. I have over the years done similar ones. Here's a water flow experiment I made on the various exhaust systems I had. This is the Healthways SCUBA regulator's exhaust. Note that the water flows right through without restriction. Note also that the bulge you describe allows unrestricted exhalations, as it bulges both ways and gives clearance between the exhaust horn and the diaphragm. This photo shows the DA Aqualung, the original regulator by U.S. Divers, and the water flowing through the exhaust duckbill. Finally, this shows the Healthways second and third generation exhaust mushroom. Note the water backup up and out the horn due to restrictions of flow. I used a Nitrile cleanroom glove as my exhaust diaphragm because materials have changed significantly since the 1950s. These Nitril materials are very tough, and resistant to various chemicals (such as sulfuric acid). They can be thin, and very flexible too. Latex also works, but latex can deteriorate over time, became "sticky" and loose their ability to function. We used the Nitrile gloves as under gloves in chemical handling, for acids, and solvents too. The problem I've had is not with toughness, but with sealing it agains the exhaust area by the wire clamp. I do get a couple of drops of water into the box and need to dry it after the dive. Concerning this breaking, yes it could be catastrophic for the regulator's function, but I have jumped into the water at the pool from a foot and a half height without problems. In the water, there is very little actual force on the membrane during the dive, as the pressures are close to equalized (see the calculation above). I am also a bit concerned about sheet silicone rubber, as I have had my Farallon mask, made of silicone rubber, split under normal wear. If you'll look at the diagram, you'll see that the duckbill's opening is located an inch or so above the lowest part of the demand diaphragm (the one which engages the demand levers). This is the difference between the water pressure on inhalation and exhalation "if" you use an inflexible closure for the area of the exhaust diaphragm. This will cause a free-flow of the regulator that will not cease on inhalation. I have experimented with a mushroom valve in the exhaust line too. I put the Hope-Page mushroom into the exhaust just above the horn, into the first convolution of the hose. It worked, but still allowed water into the hose when head-down (flooded up to the mushroom) if I stayed in that position long. John
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Post by vance on Mar 9, 2017 18:49:34 GMT -8
I'm trying out a new duckbill. I made a mold for it, and I'm going to try to incorporate some nylon from pantyhose as a reinforcement. This one will be thinner and longer, so it can be folded over the exhaust horn, as Mark suggested. I hope the thing will come off the form with the nylon cloth wrap. The cloth will only be where the fold happens, about an inch. I will post a picture of the new form when its done, and any attempts at producing a duckbill.
I think the two good ones I've made so far will work fine, if glued in. I'm just trying to make one that will stay in position without the sharp c clip, and will resist cutting by sharpish edges. Phil
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Post by vance on Mar 10, 2017 10:53:23 GMT -8
I don't know if there's any significant difference in practice, but the duckbill opening is much closer to the exhaust diaphragm than you've drawn in your diagram.
The two OEM duckbills I've seen in place were very close to the exhaust diaphragm. So, the exhaust opening, given a solid cover, would be in nearly exactly the same location as the exhaust diaphragm provides. If you raised the cover, it would bring the exhaust opening even closer to the demand diaphragm.
I'm not trying to be argumentative, here. I am asking questions and thinking about solutions.
The fundamental question for me is this: I don't see how replacing the membrane with a duckbill valve when both exhaust in the same position relative to the demand diaphragm changes anything. One should work as well as the other. However, a duckbill will keep water from entering the hose in any position.
The only thing I can think of that might affect performance is if the flexible membrane does something the duckbill doesn't, but I don't know what that would be.
Of course, all this is untested speculation and hopeful thinking. Actually trying this stuff will be the next step.
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Post by SeaRat on Mar 10, 2017 13:04:55 GMT -8
Phil,
Yes, the exhaust diaphragm does something a duckbill cannot do--it blocks the exhaust tube with air pressure. In order for the duckbill to do the same thing, there would need to be a clamp across the duckbill that reacted to the slightly increased air pressure inside the housing.
There is a simple way of checking this out in your home. Put the tank and SCUBA regulator into a bathtub, and fill the bathtub with water up to the top of the housing (regulator facing the bottom). With the mouthpiece is your mouth, turn on the air, and see that nothing escapes (normal condition. Now, with the mouthpiece still in your mouth, unclamp the exhaust hose and pull it away from the exhaust tube, but in the same line horizontally in the water. There will be air escaping.
The reason is that there is nothing in a duckbill that clamps shut the exhaust. The duckbill allows free, but one-way, air travel.
John
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Post by nikeajax on Mar 10, 2017 17:54:56 GMT -8
Hmmmmm... GRRRRRR! I was just looking at the port of this reg, then I put a straightedge on the lip. Without a domed cover for this reg a mushroom-valve wouldn't work well, and then the cover would have to clear the lever assembly too So, without doing a permanent modification to the air-horn, a duckbill is pro'lly the best thing for it. I'm thinkin' more like a USD styled, with lateral venting. Just my opinion JB
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Post by nikeajax on Mar 11, 2017 15:28:36 GMT -8
I'm thinking that bike inner tube the three of us have would make a great material for the cover. It needs a longer screw to fit the whole things on, as trying to put the screw in after is too much for my shaky fingers, but that tube material is very flexible and strong!
JB
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Post by vance on Mar 11, 2017 16:35:03 GMT -8
I have managed to get a tire tube rubber membrane on with the stock screw. Not easy, and not necessary to struggle. A longer 4-40 (I think) would make it much easier, just like using a longer screw on the ring clamp when using a silicone repro diaphragm. My concern about tire tube rubber is its tendency to crack. One would need to keep a close eye on this to avoid catastrophic failure. There is silicone sheet rubber, but I'm not convinced it will bear up using the clamp, since it cuts easily. I also found some EPDM sheet rubber, but have not gotten any, and don't know its properties.
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Post by nikeajax on Mar 11, 2017 16:47:14 GMT -8
Phil, OK buddy, how's this? While doin' my PT, I got to thinkin'... What if we take our queue from the original diaphragm: howz dat yer askin'? Get yerself some nylon fabric, then, impregnate it with sommudat sillykone ya gotz... what if you were to take some nylon and squeegee a few layers of silicone into it, eh-eh-eh? Strong and waterproof Yeah baby, bullet-proof... JB EDIT: Granted, this would not be flexible to use as a diaphragm, but with the duckbill, it no longer needs to be...
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Post by SeaRat on Mar 11, 2017 18:29:13 GMT -8
So, John, which work better? I'm guessing the USD because it allows more air to ekskape (escape)? JB Phil and Jay, ...Here is a calculation I made last year on the Healthways exhaust diaphragm: What this calculation shows is that the pressure on the exhaust diaphragm is about the equivalent of putting a two once lead weight on that exhaust diaphragm to seal it shut. And here is a diagram which illustrates the differences in the location of the exhausts between the original Healthways SCUBA and the USD Mistral/Aquamaster exhaust: Note that this drawing assumes a 3/4 inch difference between the demand and exhaust diaphragms, but I just measured it at approximately one inch of difference. John Okay, I'm going to try this one more time. Please look at the calculation. The first thing I did was calculate the surface area of of the entire exhaust diaphragm. That came out to a little over three square inches (3.27 square inches, to be exact). The second calculation simply took the pressure of fresh water per foot of depth, and convert d it to the amount of pressure inside the Healthways SCUBA case. That comes out to about two ounces across the entire exhalation diaphragm. This is enough pressure to either seal the exhaust diaphragm against the exhaust tube, or cause a free flow if only the duckbill is used for the exhaust in this position. This is what Fred Roberts meant when he said that the case is slightly above ambient pressure, and that seals the exhaust diaphragm against the exhaust tube, but only in most positions. In a had-down position the Exhaust diaphragm is not sealed by case pressure, and the backup duckbill then prevents water from entering the hose. There is a reason the Cousteau patent has the exhaust duckbill under the diaphragm. There is also a reason, the same reason, that the second and third generation Healthways SCUBA have an exhaust mushroom valve at the same level as the bottom of the primary diaphragm. That reason is to prevent a free flow. John
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Post by nikeajax on Mar 11, 2017 19:30:00 GMT -8
John, I'm sure what you have makes sense to you, but I need empirical evidence, not numbers; or showing first hand, not reading I'm pretty sure Phil may be the same way; I learn best by trial and error, and not through mathematical theorems: dyslexia is a very cruel mistress at times. Unlike words, numbers and I have a rather dysfunctional relationship I hope that makes sense to you what I'm trying to say... JB
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Post by tomcatpc on Mar 11, 2017 19:37:31 GMT -8
As a fellow Dyslexic, I have to agree with Jay's statement... Mark
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Post by SeaRat on Mar 11, 2017 20:45:49 GMT -8
John, I'm sure what you have makes sense to you, but I need empirical evidence, not numbers; or showing first hand, not reading I'm pretty sure Phil may be the same way; I learn best by trial and error, and not through mathematical theorems: dyslexia is a very cruel mistress at times. Unlike words, numbers and I have a rather dysfunctional relationship I hope that makes sense to you what I'm trying to say... JB JB, If you need a first hand demonstration, please do the bathtub exercise I mentioned on the first page. But I will try again to explain this in the above post. John
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Post by vance on Mar 12, 2017 9:49:19 GMT -8
So, John, I'm not debating the slightly superior air pressure inside the can, or how the exhaust diaphragm works. You have explained that quite well, and Fred Roberts backs you up. Let's make all that a given. What I am interested in, and confused about, is why there will be freeflow when the exhaust diaphragm is not sealing the end of the exhaust horn. You say above, "In a head-down position the exhaust diaphragm is not sealed by case pressure, and the backup duckbill then prevents water from entering the hose." So, in this head down position, and when the membrane is not sealing the exhaust horn, the regulator will freeflow? If yes, then is this caused by the rearrangement of the relationships between the diaphragm and the exhaust outlet by the diver's position (regulator upside down) which causes a drop in air pressure inside the can?
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Post by nikeajax on Mar 12, 2017 10:28:26 GMT -8
So, in this head down position, and when the membrane is not sealing the exhaust horn, the regulator will freeflow? Couldn't this be negated by further lever adjustment? JB
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Post by SeaRat on Mar 12, 2017 12:17:40 GMT -8
So, John, I'm not debating the slightly superior air pressure inside the can, or how the exhaust diaphragm works. You have explained that quite well, and Fred Roberts backs you up. Let's make all that a given. What I am interested in, and confused about, is why there will be freeflow when the exhaust diaphragm is not sealing the end of the exhaust horn. You say above, "In a head-down position the exhaust diaphragm is not sealed by case pressure, and the backup duckbill then prevents water from entering the hose." So, in this head down position, and when the membrane is not sealing the exhaust horn, the regulator will freeflow? If yes, then is this caused by the rearrangement of the relationships between the diaphragm and the exhaust outlet by the diver's position (regulator upside down) which causes a drop in air pressure inside the can? Phil, There are two separate scenarios that I described above. The first, with the diver in a head-down position is one where the case pressure is not sufficient to seal the exhaust diaphragm against the exhaust tube. In this position, the duckbill serves as a backup and prevents water from bubbling up the exhaust hose. When I dive the original SCUBA without the duckbill, I simply exhale to exhaust this intruding water, but it does make the exhaling harder. However, in this position a hard cover instead of an exhaust diaphragm will not cause a free-flow. Now, in a normal diving position, either horizontal or head-up, there is about two onces of pressure against the exhaust diaphragm, which will seal it to the exhaust tube. However, if you were to provide a hard cover to the exhaust rather than the normal exhaust diaphragm, that differential in pressure would be "felt" by the regulator, as this exhaust hose is now exposed ambient pressure at that level over the demand diaphragm. The ambient pressure on the exhaust hose is about one inch of water pressure (0.442 psi/ foot divined by 12 inches per foot, or 0.036 pounds of pressure per square inch). This is enough to initiate a free-flow through the regulator. Normally, with the levers adjusted to their maximum height, and on lower tank pressure, cracking effort for this regulator is about half an inch. I don't know whether you'll get a dribble of air leaking, or a more violent free-flow, but for a finely-tuned regulator, you should get some leakage...until the diver goes head-down. John
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