Regulator Performance when Vertical

[Luis H]

It has nothing to do with diaphragm orientation relative to the surface, it has to do with relative depth of diaphragm, mouthpiece, and diver's air canal. If the mouthpiece (and diver) are deeper than the diaphragm, it's harder to breathe.

The reason regs freeflow with the mouthpiece up is because the air in the 2nd stage is buoyant (all air in water is) and escapes out the mouthpiece opening. This lowers the pressure in the 2nd stage and allows the lever to push the valve open. Once it starts, venturi assist keeps it going.

If the reg is filled with water, it doesn't freeflow with the mouthpiece pointing up.

I can’t believe that after all this time and all the time I spent explaining that buoyancy has nothing to do with it, that you would bring that statement up again. It has nothing to do with the air buoyancy, it is just the pressure differential in the water column.

I am very sorry that I have not been able to explain it in a clear way.

You even bought a double hose regulator which should have given you an easy demonstration that it is just the pressure differential not the buoyancy.

With a double hose regulator you can have the mouthpiece opening pointing down and it will still free flow the moment the level of the mouthpiece opening is raised (about one inch) above the center of the diaphragm. The opening of the mouthpiece can stay pointing down and it will free flow when its height in the water column is above the cracking effort.


You can do the same experiment with a single hose regulator and a flexible hose.

Remove the mouthpiece on a single hose and replace it with a flexible hose. The open end of the hose can be pointing down. Raise and lower the open end of the hose. You will notice that the regulator will free flow every time the open end of the hose is higher than the center of the diaphragm (plus the cracking effort measure in inches of water column).

You can also experiment and notice that the actual orientation of the diaphragm doesn’t matter. The only thing that matters is the vertical distance (elevation) between the center of the diaphragm and the opening on the hose.

The regulator free-flows just the same it doesn't matter what the orientation of the diaphragm or the orientation of the hose opening. All that it matters is the vertical elevation difference (in the water column) between the open end of the hose and the center of the diaphragm.

The diameter of the hose doesn’t matter either, or even the length. It does have to be full of air.

This demonstrates that it is the pressure differential in the water column the only thing that matters.

I have done this experiment before, but I never had anyone film it.

Next spring when our dive club has a pool session I will try to film this experiment. Until then, you can do the experiment yourself and you can see it with your own eyes.

It is pressure differential not buoyancy.

Again, I am very sorry that I do not know how to explain this and make it clear. This is very basic fluid mechanics, but sometimes the basic are the hardest things to explain. I guess it is going to have to take a very visual demonstration.


Note: if the cracking effort in your single hose second stage is set higher than the distance from the diaphragm to the mouthpiece opening, the regulator will not free-flow when you put it in the water with the mouthpiece facing up. It is the same air buoyancy, but the pressure differential is not high enough to actuate the demand valve past with this cracking effort.



BTW: your first statement (paragraph) is perfect.

 

[tbone1004]

It has nothing to do with diaphragm orientation relative to the surface, it has to do with relative depth of diaphragm, mouthpiece, and diver's air canal. If the mouthpiece (and diver) are deeper than the diaphragm, it's harder to breathe.

note I didn't say diaphragm orientation relative to the surface, I just said diaphragm orientation. It is usually easier to explain as orientation to the surface as all divers have seen the reg freeflow with the mouthpiece up and have been told to turn it mouthpiece down to get it to stop.
My comment was about diaphragm orientation as related to the mouthpiece, hence the comment about the poseidons being able to roll around vertically with no issue even though the diaphragm orientation to the surface does change, but you roll to the side, it can get stiff to breathe or freeflow.

 

[halocline]

With a double hose regulator you can have the mouthpiece opening pointing down and it will still free flow the moment the level of the mouthpiece opening is raised (about one inch) above the center of the diaphragm. The opening of the mouthpiece can stay pointing down and it will free flow when its height in the water column is above the cracking effort

It is pressure differential not buoyancy.

Again, I am very sorry that I do not know how to explain this and make it clear.

Yes, I do understand about the pressure (depth) differential, and I know exactly what you are referring to with regards to the double hose mouthpiece pointing down, but still flowing if it is raised above the 2nd stage. You have nothing to apologize for with regards to your explanations over the years. (Although I'm sure it's frustrating for you!)

However, in this example, the OP was talking about a single hose 2nd stage freeflowing when introduced to the water mouthpiece up, as do almost all well-tuned 2nd stages if they are either pushed into the water mouthpiece up or removed from a diver's mouth, with the mouthpiece pointing up. The very same 2nd stage likely would not freeflow mouthpiece up when the stage is filled with water, even though the pressure differential between the diaphragm and the mouthpiece opening is the same. (About 1" water) This is true as long as it's tuned to accommodate for the pressure differential. And this is why there must be something at work in addition to pressure differential in this specific case. The only thing that makes sense is loss of pressure in the 2nd stage as air begins to escape.

Taking your example of a flexible tube replacing the mouthpiece, with the opening facing down, the reg will freeflow as soon as the pressure (depth) differential exceeds the cracking pressure. That's pretty much exactly what you said, right? I understand that and agree with it.

What about a situation where the reg freeflows when the pressure differential between mouthpiece and diaphragm is less than the cracking effort? Because as far as I can tell, that's what is being described in this thread. What about a 2nd stage freeflowing with the mouthpiece horizontal in the water, at the same depth as the diaphragm? It happens frequently. That type of free flow cannot be explained by depth differential. The only logical explanation is loss of pressure in the 2nd stage for some reason, followed by venturi assist maintaining the flow.

By the way, I'm heading back to your homeland in January. Tal vez podemos platicar en tu idioma nativa antes de entonces.

 

[Luis H]

Ok, I think that I am following part of what you are missing.

When a second stage is flooded, there is no pressure differential. The same column of water that exist on the outside also exist on the inside. Therefore, as the pressure increases with depth on the outside of the regulator, it also increases at the exact same rate on the inside (because it is flooded).

An underwater habitat or a dive bell with the bottom open to the sea will have the same pressure as the depth at the water air interface. The inside of the bell or habitat will all be at the same pressure, because the air column inside the air space is essentially weightless (as compared to the water column outside.

If the bottom of the bell is at 30 feet, the inside pressure on the entire bell is at 30 feet even if the bell is 20 foot tall and the top of the bell is only exposed to 10 feet of external water pressure. But if the bell floods, there will not be any pressure differential.



Back to your other regulator examples.

“What about a situation where the reg freeflows when the pressure differential between mouthpiece and diaphragm is less than the cracking effort?”

You may see the air escaping or you may see a leak, or if you drop the regulator in the water hard you may induce the venturi to take over and free-flow. But if you lower that same regulator slowly into the water with the mouthpiece up it will not free-flow.

When I don’t have a Magnehelic handy, I will test the cracking effort of a regulator by slowly dipping it into water container slowly. If you do it fast, you may trigger the venturi flow.

“What about a 2nd stage freeflowing with the mouthpiece horizontal in the water, at the same depth as the diaphragm?”

Again you may see bubbling while the regulator is filling up or you may have a leak (or you may have accidentally triggered the venturi flow), but if there s no pressure differential, the demand vave will not be actuated. The demand valve only responds to pressure differential.

A strong venturi flow does create a vacuum, causing pressure differential. This is a dynamic flow phenomena that has been designed into most regulators and once the flow is initiated even by a little tap or by moving the regulator in the water, it will only stop the mouthpiece s partially blocked. Even one finger will disrupt the flow stopping the venturi and its associated vacuum.

A well tune regulator can be so sensitive that initiating the venturi flow is very easy and I have done it with a Scubapro 109 by just moving a flooded regulator in the water. regulators with a hard front cover are not as sensitive.


I hope I was able to explain all your observations. Buoyancy is not the direct explanation to any of those observations.

Buoyancy is the result of the density/ weight (mass) difference. The pressure differential inside a dive bell (or a regulator) is also the result of the weight/ mass difference between the water column outside and the air column inside. Therefore, there is a connection between mass/weight, buoyancy, and pressure differential. It is important to understand the connection and what actually causes what. The density/ weight difference causes both pressure differential and will also cause buoyancy, not the other way around.


Again, I hope this is clear.

For the record, I could not explain it better in Spanish even if I tried.

 

[Couv]

What about a 2nd stage freeflowing with the mouthpiece horizontal in the water, at the same depth as the diaphragm? It happens frequently. That type of free flow cannot be explained by depth differential. The only logical explanation is loss of pressure in the 2nd stage for some reason, followed by venturi assist maintaining the flow.

Halo is describing something similar to an oddity I've experienced quite a few times. Imagine you are laying on the bottom with your ear in the sand because you're trying to see that lobster or splendid toad fish. After you're finished exhaling-but before you inhale, some gas continues to vent through the exhaust. I used to think this was something caused by the Venturi effect; but because it stops all on its own there is something else going on. In addition to the length of the exhaust tee, I believe what is really happening is the gas is creating it's own "tube." Think of a long rather than spherical bubble (like an animal balloon.) The top of the bubble is higher in the water column than the center of the diaphragm. In turn, it causes a drop in pressure into the case through the still open exhaust valve.

The effect is similar to a double hose regulator siphoning air after exhallation-but without a physical tube. (Thank goodness for the new Argonaut DSV)

 

[Kharon]

Note: if the cracking effort in your single hose second stage is set higher than the distance from the diaphragm to the mouthpiece opening, the regulator will not free-flow when you put it in the water with the mouthpiece facing up. It is the same air buoyancy, but the pressure differential is not high enough to actuate the demand valve past with this cracking effort.

Is this why a de-tuned reg/octo does not freeflow?

 

[Couv]

Is this why a de-tuned reg/octo does not freeflow?

Yes.
The advantage of an adjustment knob (again, nothing to do with balanced vs. unbalanced) is so the diver can tune/de-tune the cracking effort.

 

[tbone1004]

Is this why a de-tuned reg/octo does not freeflow?

yes. if cracking pressure exceeds the space between the diaphragm and the mouthpiece, it will not freeflow when placed in the water mouthpiece up

 

[kelemvor]

I noticed in this thread help with my brand new Atomic B2 that the performance of a regulator while vertical in the water can be a concern. I like to pull up into a vertical position once in a while - better field of view, better situational awareness, and it gives my neck a break. Is this a first stage or second stage issue? And, are there certain designs or brands that are better when vertical than others or is it just tuning?

It sounds to me like tuning. I know this thread has been focusing on some of the finer points of regulator operation but... I can't really tell any significant difference in the performance of any of my regulators when vertical vs horizontal. That includes a crappy mk2/r295 that I paid $175 for brand new.

I had a medial issue requiring my neck to be almost completely fused. That means to look "ahead" of me, I have to go slightly or fully vertical. I do it almost every dive now. My regs don't breathe significantly harder.


Now, I used to volunteer at an aquarium cleaning animal tanks. The cheaper reg performs noticeably worse than my s600/mk25 when I am completely inverted. The mk2/r295 would be a very hard breather but the s600/mk25 didn't change a lot (it did change some, but not much).


Unless you really do mean when the reg is out of your mouth and floating on the surface... in which case - just pretend I didn't post this irrelevant message.

 

[tdallen]

Actually @kelemvor and @tbone1004 , you're right on target. I was more concerned about changes in the breathing effort of the in-use first/second stage depending on the orientation of the diver/regulator in the water. Your replies were very helpful, thank you. There's been lots of other eye-opening information in this thread that I had no idea was related to my topic... but this is Scubaboard and that seems to happen frequently .