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Herman
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To valve or not to valve, that is the question.

Sun Jan 12, 2014 9:07 am

Sorry for the bad Shakespeare pun. :)
With the introduction of the DBE and now the Kraken, I though I would start a discussion on whether or not mouthpiece valve are needed on “modern“ DH regs. Are they better left out, kept in or some combination of both ? I know the modern valves are very good and add little to the breathing resistance but still it adds some. Thinking it though and doing some simple testing, I have come to the conclusion that keeping the supply side valve in and removing the exhaust is my preference. My "logic" is this, on the supply side I have the ability to adjust the breathing resistance and vary the venturi so I can compensate for the little bit of resistance it adds. In addition, the valve helps prevent water from getting into the hose and back into the reg. As I measure breathing resistance on the bench, the exhaust is somewhat higher than the supply so anything I can do to reduce it is a plus. Granted, I am talking about small improvements, not major gains.
I see 3 advantages to keeping valves in the exhaust side, one is in the unlikely event of a DBE, exhaust valve or hose failure, it will at least keep most of the water from getting back into the mouthpiece, the other is it does help when there is some water in the exhaust hose that is being a nuisance and lastly, it does keep some water out of the exhaust hose when you have the mouthpiece out of your mouth. With the common use of octos on “modernized” DH regs, the failure of an exhaust valve or hose is not as big of an issue as it once was and once cleared, water from having the mouthpiece out is not an issue so I see those as small benefits compared to the improvement in breathing resistance with it out. .
SO, the question is, are those advantages worth the increase in exhaust resistance, all be it slight? . What do you guys think ? Am I missing something important?
Herman

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SurfLung
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Re: To valve or not to valve, that is the question.

Sun Jan 12, 2014 10:27 am

- I'm figuring some of your reason for considering this is Nemrod's testing on his exercise bike. But in that case, I don't think exhale effort was a problem until he was at maximum effort... Beyond the capabilities of all but the Argonaut and XL.
- And even in those two cases, wouldn't exhaling be easier in actual diving with water pressure on the lungs and (on the Argonaut) the exhale port being above the lungs in lower pressure?
SurfLung
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Herman
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Re: To valve or not to valve, that is the question.

Sun Jan 12, 2014 12:03 pm

Actually no, I have been playing with this since the DBE came out and more after I got the Argo cans. It is more based on bench test compairing inhale values VS exhale and some playing around under water. I realize that UW is different than on the bench but it has always seemed to me that underwater on a very well tuned reg like a Phoenix or the Argo(at least to my liking - I go a little heavy on the venturi) that the inhale is somewhat easier than the exhale. It's not bad by any strech but it is something to tinker with.
Herman

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antique diver
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Re: To valve or not to valve, that is the question.

Sun Jan 12, 2014 1:23 pm

Scientific testing at least as far back as the 1960's (Glen Egstrom, UCLA) identified exhalation effort to be an important limitation factor in working dives, but in a normal relaxed diving scenario I seem to be more sensitive to inhalation effort than exhalation effort. That changes under a heavier workload, when I do feel the exhalation resistance to be more noticeable. Since I seldom encounter the latter situation, I feel comfortable leaving the MP exhaling valve in place for the reasons you stated.

I have even run into one situation that prompted me to install a stiffer MP exhaling valve on my Trieste. It inhales extremely easy due to the change to a softer, reshaped diaphragm, plus tampering with it to produce a stronger venturi. That venturi had caused a small amount of air to be lost out the exhaust during my inhalations, and the stiffer exhaling valve helped control that while not being a problem on exhaling resistance.

On the other end of the MP, I sure like the open and easy feel of inhalations when I dive without the MP inhalation valve in place. That can make a noticeable improvement in a marginally performing double hose reg, especially when totally removing the wagonwheel and inserting a thin-walled tube to support the hose clamp. But there are downsides to removing that valve, such as the possibility of a partial or complete flooding of the regulator body. Testing the recovery from that situation has been successful, but I still have the feeling that I am safer with the inhalation valve in place.

Comments and suggestions always welcome...
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phsdive
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Re: To valve or not to valve, that is the question.

Sun Jan 12, 2014 6:17 pm

Good question. I would leave them both in. I think they add very little to any effort on both sides. From memory the early USD catalogues made a point of advertising that the reg now came with the clear eze (sic?) mouthpiece. With a flooded mouthpiece you only have to clear a small amount of water prior to taking a breath (with the exhaust valve in). Without the mouthpiece exhaust valve you are pushing a lot more water out to fully clear the line. Buddy breathing in a stressful situation would be more difficult and for some impossible. If you are required to work hard anything like Nemrods experiment I would use a divator or a kirby morgan on ss.

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Nemrod
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Re: To valve or not to valve, that is the question.

Mon Jan 13, 2014 12:15 am

My cage valves are staying in. The exhaust effort with the standard neoprene duckbill is acceptable and with the DBEV it is in my opinion slightly better. But, the Argonaut takes a big jump, noticeably less effort. I do not think there is any reason to do without the safety afforded by cage valves, even on just the exhaust side.

I have measured these pressure with my Magnahelic that has a positive scale. Thing is, as has been noted, typical horizontal positioning of the diver when using a double hose regulator, the exhaust valve being above the lungs at a lower pressure, assists exhalation.

I do most definitely notice exhalation effort, it is something I have payed attention to for many years. As I have said, I do not think cracking effort, within reason, has nearly the effect upon WOB that either exhalation or inhalation effort has. Since, it is obvious from the ASTM charts I have seen for various regulators and it is clearly noticeable, using my Magnahelics on my test bench, for all of my (well) tuned double hose regulators, especially evident on the Tekna T2100 and the AMF MR12 with the assist tube and on my Titan XL, the inhalation values go (slightly) positive once the venturi is established at least through portions of the inhalation cycle.

I just do not think enough is gained by removing the exhaust cage valve to justify doing it.

If one hooks up a Magnahelic, as I have done, one at the outlet horn, one just upstream of the cage valve and one inside the mouthpiece interesting things are seen. The positive pressure I have mentioned are not seen by the Magnahelic inside the mouthpiece or if so they are much attenuated. The Magnahelic at the horn shows the greatest positive response. Measuring cracking effort, I am seeing as much as .4 inches difference (aaahhhhhhh, sorta) across the intake cage valve.

This indicates to me that there is an opportunity there for improvement.

And, this will cause a fuss, but I can measure difference between the single hose mouthpiece adapter I made a few years ago and the curved USD mouthpiece, advantage, curved USD mouthpiece. To see the difference, the Magnahelic has to be actually in the divers mouth, I used an aluminum tube through the mouthpiece to do the experiment.

I have noticed with high performance single hose regulators, specifically the T2100 and my wife's Legend, if I install those small diameter (Scubapro 109 I think it is or the size used on the early USD stuff) that the regulators will have a tendency to flutter. Yes, yes, they are stretched over the outlet but they pinch down once past the suppoting outlet tube. I have mentioned this before. I only mention it now to consider this in the development of any future design that utilizes off the shelf single hose mouthpieces, get the jumbo ones, :lol: . The mouth tube must be as large in diameter as possible with no restriction.

James

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