Single vs two-hose image questions?

[Nemrod]

Ultimately, WOB is about CO2 buildup, not the differential pressure itself.

Yes, it does feel easy to pull a relative vacuum through a tube with your lungs in the 6-12" range. The difference is "feeling easy" when that vacuum is acting on small area is understandably misleading when apply it to WOB.

Sucking or blowing against a differential pressure that is perceived as insignificant can quickly cause a buildup of CO2, which causes that "air starved" sensation. A case in point are the absurdly long snorkels sold as pool toys in the 1950s.

Even if you could ventilate through a 3 feet long snorkel, and you cannot, all you would be doing is breathing the same increasingly CO2 rich air over and over.

Applied to scuba regulators, and I multiple times have worked in a scuba store, customers are always impressed with or concerned with ease of inhalation, specifically the percieved cracking effort. I never had anyone say, wow, this regulator exhales really easy or this regulator has a really strong Venturi effect. But those two things are more important than the cracking effort alone for the overall WOB.

Those ginormous ping pong ball snorkels would give me a headache, so would those twin snorkel full masks. But who cared, they were coo! I would suggest not taking a coil of hose fitted with a valve to the bottom of a pool and then sticking it on or in your mouth and then opening the valve to the hose. One end is at atmospheric pressure and now you are on the other end at more than atmospheric pressure. This is not good. Well, if it is a cheap hose it will just have collapsed. Better get a kink proof.

James

 

[Jcp2]

To avoid co2 buildup in the dead space you could exhale through the nose. Doesn’t solve the pressure differential though.

 

[Nemrod]

To avoid co2 buildup in the dead space you could exhale through the nose. Doesn’t solve the pressure differential though.

Well, yes, but the mask fogs up. I built a snorkel when I was a child that had one way valves in it, air could only enter the tube and then exhaust at the mouthpiece. But try as I might it still was not a solution to a scuba tank . Hey, mom, can I take the scuba class with Rex (my older next door neighbor friend) at the Y, please!

It is the Venturi and the low exhalation effort that make a dh regulator appealing to me, the two variables least appreciated.

N

 

[Luis H]

There is a lot of talk about WOB (Work of Breathing) and pressure differential, cracking effort, and now CO2 build up.

It is probably a good time to include the technical definition (as used in physics) of what it means to do work. This may be very basic or common knowledge, but I thought it may help.

“In physics, work is defined as a force causing the movement—or displacement—of an object. In the case of a constant force, work is the scalar product of the force acting on an object and the displacement caused by that force.”

“UNIT OVERVIEW Whenever we use force to move something, we are doing work. ... Students will learn that the amount of work required to move an object depends on the amount of force needed to move it as well as the distance the object will be moved.”

Those are just two (of several) basic definition I found using Google.

I decided to quote something from the internet, just because, I am not very good at explaining some stuff. I am an engineer with a minor in applied physics, but I am not a professor.


To my point is that we are not just talking about pressure differential (or a force time an area), when we are talking about work. Notice that force and pressure are related by the area. I think we all know that. And that can be described as the effort required to do “work”. But in physics, in order to do work, you have move some amount of “mass”.

The same applies to the work required to move the mass of a gas (air), both during inhalation and exhalation.

BTW, we often talk about the volume of the gas or the volumetric flow rate, but in many case we should be talking about the mass flow rate. We all know that they are related by density, but when it relates to the work the mass flow is the factor.

They used to advertise vacuum cleaners by lifting a bowling ball. Turns out, that was not very hard with a big nozzle that could create a seal. We are now a bit wiser and we now know that we need the flow in addition to the “static suction”.


While I am at it, we might as well mention energy, in physics, the capacity for doing work.

The most common definition of energy is the work that a certain force (gravitational, electromagnetic, etc) can do. Due to a variety of forces, energy has many different forms (gravitational, electric, heat, etc.) ... According to this definition, energy has the same units as work; a force applied through a distance.

I mention energy, because the elastic (or potential) energy of the compressed gas in a scuba cylinder is a major source of energy in open circuit Scuba (as opposed to a closed circuit re-breather). That energy is in part harnessed with venturi flow, etc.


I don’t know if this helps… I hope it does.

 

[John C. Ratliff]

Even if you could ventilate through a 3 feet long snorkel, and you cannot, all you would be doing is breathing the same increasingly CO2 rich air over and over.

Applied to scuba regulators, and I multiple times have worked in a scuba store, customers are always impressed with or concerned with ease of inhalation, specifically the percieved cracking effort. I never had anyone say, wow, this regulator exhales really easy or this regulator has a really strong Venturi effect. But those two things are more important than the cracking effort alone for the overall WOB.

Those ginormous ping pong ball snorkels would give me a headache, so would those twin snorkel full masks. But who cared, they were coo! I would suggest not taking a coil of hose fitted with a valve to the bottom of a pool and then sticking it on or in your mouth and then opening the valve to the hose. One end is at atmospheric pressure and now you are on the other end at more than atmospheric pressure. This is not good. Well, if it is a cheap hose it will just have collapsed. Better get a kink proof.

James

James,

We have learned very little about the volume of these full-face snorkeling masks over half a century ago. The whole concept is again there, as is shown by the full-face modern snorkeling masks. Here's one on Amazon right now:

 

[John C. Ratliff]

I got a double post, so I'll post an image of the full face snorkeling mask. You'll note that the mask has an inner mask, and they claim to have separate routes for air entry and exhalation. But there is no fit testing of this inner mask, and they also advertise that "natural breathing" is all that is necessary for use of this mask. But this "natural breathing" is very shallow, and has the potential for inhaling a large amount of the exhaled air from the mask. There have been some fatalities in Hawaii associated with these full face snorkeling masks, and some of the tour boats now will not allow them. If used, the snorkeler needs to use deep breathing to make the mask perform correctly, I think.

SeaRat

 

[Nemrod]

I got a double post, so I'll post an image of the full face snorkeling mask. You'll note that the mask has an inner mask, and they claim to have separate routes for air entry and exhalation. But there is no fit testing of this inner mask, and they also advertise that "natural breathing" is all that is necessary for use of this mask. But this "natural breathing" is very shallow, and has the potential for inhaling a large amount of the exhaled air from the mask. There have been some fatalities in Hawaii associated with these full face snorkeling masks, and some of the tour boats now will not allow them. If used, the snorkeler needs to use deep breathing to make the mask perform correctly, I think.

SeaRat

I am just gonna say it, damn the torpedos, but anyone who needs that needs to stay out of the water. That masks needs an exhalation valve and a one way in the intake tube to prevent recycling of CO2. On the other hand, I do not want to know .

James