mouthpieces and mouthpiece valves

[duckbill]

I thought I'd take the initiative and heed Bryan's hint. I think this subject is a great thread on it's own. I realize it is not "my" thread, but I hope the discussion will continue on here as it was in it's former home (New Phoenix Owners).

I think you will find that any mouthpiece that uses the modern single hose mouthpieces will result in "harder" breathing. If you look you will see that most USD/Voit and other well known double hoses units that perform well have large mouthpieces with opening that have a large flow area. This is absolutely critical with a double hose regulator (remote venturi) and this important feature has been forgottern with the New Mistral and rebreather units (who complain of stiff breathing). I think thee may be some extra large mouthpieces that might work alsmot as well as a USD double hose mouthpiece but I cannot recall any at the moment. Single hose regulators because the venturi vane is right at the mouthpiece can make do with small mouthpieces, the Phoenix or any other double hose cannot and will not perform correctly with the small single hose mouthpiece grafted on---they are to small in area--which will create back pressure that will greatly reduce performance. I have proven this to myself sufficinetly to no longer question it. Any mouthpiece, homeade or whatever must utilize as large an opening as is possible with as large a mouthpiece (internal passage) as is possible.

James

I think that is an EXCELLENT observation, James. It seems very true that the venturi of a single hose reg pointing directly into the mouthiece can make up quite a bit for any loss due to the mouthpiece size.

The Hope-Page mouthpiece uses standard mouthpieces.

Interesting.

[Bryan]

EXCELLENT IDEA.....Thank you

And for what it's worth......If I'm sure that no one else might borrow my double hose I don't put a mouthpiece valve on the intake side....It makes a noticeable difference as some of you have already pointed out.......THIS IS JUST SOME CRAZY S**T I DO. I AM NOT SAYING OR RECOMMENDING THIS TO ANYONE ELSE.

[Nemrod]

Not all single hose regulators have the same size mouthpiece. I first noticed the extra large opening mouthpieces with the first Tekna T2100 I bought in 1978 or so. These Teknas were very back pressure sensitive, backpressure would cause a feedback into the pilot valve system that resulted in severe flutter. The large mouthpiece openings were required to prevent that. In the instruction manual they made note to the diver not to place their tongue or clench down on the mouthpiece or anything that restriced the opening or flutter would result or at least reduced performance.

Playing around with various bits of homemade stuff for experimentation leads me to believe that there is no way your going to get optimum flow for a double hose using any current single hose mouthpiece I have seen including the jumbo type that many high performance single hose regs now have--they are just to small.

I have mentioned it before but those silicone cage valves make a huge difference vs the black rubber ones. As Bryan mentions, removing the intake cage valve will noticeably reduce inhalation effort--not recommended due to flooding possibilities.

I keep redaing various articals on rebreathers and how many of them breath rarely poorely. ThenI look at their hoses and mouthpieces and these DSV valves and quickly one can see that these rigs are not so well thought out in many areas, this is one. I think most of these mouthpieces despite my enthusiasm for a shut off valve will result in poor breathing.

Such a mouthpiece assembly would need large openings and large mouthpiece section and large silicone cage valves.

James

[luis]

I measured the mouthpiece opening on four USD curved mouthpieces and three single hose mouthpieces (2 Scubapro metal adjustable and one D400).

The opening in USD curved mouthpieces measured about 1.28 inches wide by about 0.36 inches height. Since the opening is basically a rectangle the area is approximately 0.46 inches square.

The opening on the single hose mouthpieces is basically a central rectangle with half circles on each side. The average height was 0.5 inches and the total width was 1.06 inches. The total area for this opening is approximately 0.48 inches square.

In conclusion the area of both mouthpieces is almost identical (so close that any measuring inaccuracy could offset the results) or perhaps the single hose mouthpiece is a tiny bit larger.
Your dimensions may vary.


So let’s talk about valves. I will try to take some dimensions, maybe this evening.



Below is a copy of my previous post:

IMHO the area of the open check valve is far more critical that the open area of the mouthpiece.

I have a new Mistral just for parts and experimenting, so I will instrument the mouthpiece and test it against an original curved USD mouthpiece sometime in the near future.

Again IMHO I think the new Mistral mouthpiece may win (if it is even measurable) because of the valves. We will see.


The new Mistral has a basic (non-pneumatically balanced) down stream demand valve second stage with a small diaphragm (about the size of a single hose diaphragm). IMO that is its major issue.




The combination of the spokes on the one way valve wagon wheals plus the rubber valve disc itself adds a substantial resistance to the air flow. I have measured that to be in the order of 0.3 to 0.5 inWC.

[duckbill]

Without drawing any conclusions or opinions, these are the measurements that I have for some different mouthpieces and mouthpiece valves. I can provide the measurements and calculations for anyone interested.

Mouthpiece Areas in Square Inches:
Dacor R-4- .37
Healthways Hope-Page- .40
standard single hose (from the regulator body opening)- .45
USD curved- .45
New Mistral- .51
USD straight- .59
(Of course, the airflow space around the edges of the lifted mushroom valve itself may be even less. This would depend, in part, to the flexibility and diameter of the valve.)

Wagon Wheel Air Flow Areas in Square Inches:
New Mistral- .783 (a little less, as the spoke connections are rounded)
Healthways Hope-Page- .572
Dacor R-4- .580
USD- .637

If anyone can easily get a New Mistral wagon wheel out without damaging it, please let me know how.


-DOTD

[pescador775]

The mouthpiece on my brass module is from a Scubapro R109 and has approx dimensions of 3/8 X 1 1/8. The mouthpiece on my stock RAM is 3/8 X 1 3/8. The double hose mouthpiece is, therefore, larger in area. Comparing the two, the larger size of the dbl hose mouthpiece is very apparent. I checked a modern mouthpiece from a USD single hose and its portal shape is much different from the old Scubapro, as Luis indicated. I didn't measure it but it appears to be as described above.

The valves in the brass module are stock USD with silicone mushrooms. The Nemrod hoses are approximately 2 inches longer than stock USD hose. Also, the corrugations are seemingly more tightly spaced. I would guess the different hoses have something to do with extra resistance as well as the smaller mouthpiece.

[Nemrod]

The single hose mouthpieces affix to the regulator via a tube. This tube is much smaller than the funnel shaped area leading to the "mouthpiece" of the cureved USD unit. You neeed to measure the ID of the tube and it's total volume.

Not only does the tube reduce area but it sits at 90 degrees to airflow (ina double hose). The flared and funnel shaped area of the USD curved mouthpiece does not intersect at 90 degrees.

Calculating is great but art is sometimes better, the art of the curved USD mouthpiece is that calculations aside it flows more air with less resistence---that is what I think---lol--and can observe.

I am not coming up with the same numbers you guys did either. I have the USD mouthpiece nearly twice the area where it departs from the cage section.

Comparing the mouthpiece of my Legend to the Tekna, the Tekna is noticeably larger. Such a large opening might be useful with adapting to a double hose.

Two years ago I took a cracked Tekna second stage and cut the threaded LP mechainism end off leaving only the mouthpiece (and rendered useless diaphram) and stuck it into the USD hoses with a rubber adapter to keep my cage valves. I think I posted a picture. It was just for testing the mouthpiece--I quickly noticed an increase in breathing effort.

There is more to it than measuring the area right at the mouthpiece outlet, the internal volume of the mouthpiece assemly is consideably greater and the USD mouthpiece does not have a tube stuck in it either.

James

[pescador775]

The single hose rubber mouthpiece on my brass module has an internal shelf so the shelf rests on the rather thin, metal tube and a measurement of the tube or mouthpiece ID (front) is a true dimension for air flow purposes. I think most mouthpieces are made this way. If so, I would have no issue with the way Luis made his measurements, as long as he measured inside the lugs that is.

[duckbill]

You have successfully confused me.
The mouthpiece areas I was measuring are the areas of the openings of the mouthpieces proper at their smallest dimensions (the part that actually goes in your mouth- not the area of the entire body/"tube"), since this is the point of constriction. In the case of the single hose second stage and the Hope-Page mouthpieces, I measured the actual ID of the mouthpiece body openings where the rubber mouthpieces attach.

So, if you meant the "tube" of the single hose second stage as being the portion of the regulator body on which the rubber mouthpiece is affixed, that is what I measured for the single hose (Conshelf VI) and Hope-Page mouthpiece measurements.

The single hose mouthpieces affix to the regulator via a tube. This tube is much smaller than the funnel shaped area leading to the "mouthpiece" of the cureved USD unit. You neeed to measure the ID of the tube and it's total volume.

Not only does the tube reduce area but it sits at 90 degrees to airflow (ina double hose). The flared and funnel shaped area of the USD curved mouthpiece does not intersect at 90 degrees.

You are correct on that last point. The mouthpice intersects the body at less than 90 degrees (tighter bend), since the body angles back to the hoses. I don't see how this is a benefit. (Doesn't one of the Nemrod mouthpiece bodies sweep forward to the hoses?)

I am not coming up with the same numbers you guys did either. I have the USD mouthpiece nearly twice the area where it departs from the cage section.

Again, my measurements are of the actual "mouthpiece" for the reason stated above.

There is more to it than measuring the area right at the mouthpiece outlet, the internal volume of the mouthpiece assemly is consideably greater and the USD mouthpiece does not have a tube stuck in it either.

With the actual "mouthpiece" airflow area being so much smaller than the area of what I think you may mean by the "tube" (body?), I believe the mouthpiece openings offer the greatest resistance to airflow. The wagon wheels may be even more restrictive, but it's difficult to tell just how much the valve opens around it's edges during a standard inhalation without transparent components or extreme calculations of airflow and rubber deflection. Maybe Luis has some ideas on this.

I hope this clarifies what my measurements represent.
My measurements are there for others to draw their own conclusions. Someone else can measure the mouthpiece body internal dimensions and discuss the ramifications. I don't think that number plays a very big role, but the 90 degree turn of the airflow might. As far as I know, all double hose mouthpieces share that trait to some degree.



-DOTD

[Nemrod]

I am not talking about the hose to mouthpiece assembly intersection angle. Take a curved USD mouthpiece and look down on it in plan view. Note that the mouthpiece opening is shaped like a funnel smoothly transitioning into the cage valve area rather than straight in with an acute 90 degree intersection as would likely be the case if you adapted a single hose mouthpiece to a double hose.

I also compared the actual opening, originally to my Legend, Tekna etc. The Tekna mouthpiece does have nearly the same area. The Legend is smaller as is my Voit MR12. We must have different rulers or something.

As to the cage valves, the silicone valves are noticeably better.

I have had a hose that was trimmed to much on the collar. This hose interfered with the opening of the exhaust side of the mouthpiece cage valve partially restricting the valve--it was very noticeable.

I like simple experiments, I can take a standard single hose mouthpiece from my spares, put it in my mouth and I immediantly notice some resistence. I can take an empty--no cage valves---USD mouthpiece and I feel no resistence.

You tell me, why does it differ in practical observation?

I measure an area of .44 on the Legend and .52 on the curved USD mouthpiece at their max restriction. The single hose mouthpiece maintains that same diameter it's entire length, the USD curved mouthpiece is over twice the area as it transitions into the main body.

James

[Bryan]

I don't have anything quite that technical going for me.....But I do know that if you cut out the center of a wagon wheel and just use the outer rim of the wheel to keep the mouthpiece and hose assembly rigid it breathes even easier!! Less resistance is good....

[capn_tucker]

I don't have anything quite that technical going for me.....But I do know that if you cut out the center of a wagon wheel and just use the outer rim of the wheel to keep the mouthpiece and hose assembly rigid it breathes even easier!! Less resistance is good....

Do you ever have flooded regulator problems with this setup? Just curious..

[Bryan]

Do you ever have flooded regulator problems with this setup? Just curious..

I do not recommend or advise anyone to use this setup. There is a reason USD put valves in the mouthpiece….. It’s a better than average chance that you will play choke and puke at some point and worst case scenario do the crappie flop using this configuration.

[capn_tucker]

Not to worry, have no intentions of trying that. Wouldn't want to take a chance on flooding the regulator, let alone the choke -n- puke scenario...

[eskimo3883]

Hi Bryan,

At first I liked the idea of the open wagon wheel but now I am wondering. During exhalation this would add a bit of dead-volume and a potential for CO2 storage until the next breath. Could this kick up your CO2 loading? If just the added volume of a full face mask can lead to CO2 build-up this seems like it could be in the same direction.