Single vs two-hose image questions?

[John C. Ratliff]

James,

I think that my A.I.R. I regulator by Scubapro will out-perform the D400, as the diaphragm is the exhalation valve, and it's oriented opposite, up instead of down.

Now, concerning the op-ed's question, here's the original diagram by Bill Barada and published in Let's Go Diving, U.S. Divers Company, 1962. Bill had some interesting things to say, and remember he wrote this in the early 1960s.

I. SELECTING A REGULATOR

The regulator is probably the most important single piece of equipment selected by a diver. The choice should be made with extreme care, to be sure its breathing characteristics are adequate to meet the individual's requirements. Air consumption increases in proportion to depth and exertion. An inexpensive regulator, adequate for shallow water sport diving, is often incapable of delivering the amount of air required by a diver working in comparatively deep water. The internal mechanism and design determine air flow and suction characteristics in either single or double hose regulators, and performance cannot be determined by "test breathing" in the air or in a swimming pool. Prefossional perfarmance can only be measured by sensitive laboratory instruments, which calibrate the suction effort required in order to obtain the necessary flow of air. "AQUA-LUNG" regulators are available from the manufacturer..."

SeaRat

 

[rx7diver]

I think that my A.I.R. I regulator by Scubapro will out-perform the D400, as the diaphragm is the exhalation valve, and it's oriented opposite, up instead of down.

I would like to try a SP Pilot and a SP A.I.R. 1 some day. But, honestly, I am quite satisfied to dive my SP D400 > G250 > Balanced Adjustable "forever" for the type of recreational diving that I do now. And my U.S. Divers DA Aqua Master PRAM, too--not for work of breathing considerations, but because it routes my exhaust bubbles behind my head, away from my face mask and ears, and therefore provides an underwater experience that somehow seems much more immediate and intimate (to me).

rx7diver

 

[Nemrod]

James,

I think that my A.I.R. I regulator by Scubapro will out-perform the D400, as the diaphragm is the exhalation valve, and it's oriented opposite, up instead of down.

Now, concerning the op-ed's question, here's the original diagram by Bill Barada and published in Let's Go Diving, U.S. Divers Company, 1962. Bill had some interesting things to say, and remember he wrote this in the early 1960s.


SeaRat

The volume consumed or demanded by the diver remains the same at depth as on the surface. What changes is the density of the gas. The volume or tidal volume of the divers lungs do not change appreciably with depth so he is moving the same amount of gas in terms of volume at 100 feet as at 0 feet. It is just more dense. I am not sure I can agree with Mr. Barda on that point that a diver is consuming more volume at depth. And today, some, what, 60 years of water under the bridge, almost any modern regulator can supply more than enough air for a diver at sport diving depths and beyond with the limitation being the tank valve generally, not the first or second stages.

I just watched a video of 135 divers in Korea being fed by one (1) Scubapro Mark 25! Of course, they are not explaining that the hoses to supply that many divers would act as an accumulator but still, is there a first stage regulator anywhere that appreciably can flow more gas than the Mark 25?

James

 

[John C. Ratliff]

The volume consumed or demanded by the diver remains the same at depth as on the surface. What changes is the density of the gas. The volume or tidal volume of the divers lungs do not change appreciably with depth so he is moving the same amount of gas in terms of volume at 100 feet as at 0 feet. It is just more dense. I am not sure I can agree with Mr. Barda on that point that a diver is consuming more volume at depth. And today, some, what, 60 years of water under the bridge, almost any modern regulator can supply more than enough air for a diver at sport diving depths and beyond with the limitation being the tank valve generally, not the first or second stages.

I just watched a video of 135 divers in Korea being fed by one (1) Scubapro Mark 25! Of course, they are not explaining that the hoses to supply that many divers would act as an accumulator but still, is there a first stage regulator anywhere that appreciably can flow more gas than the Mark 25?

James

James,

Bill Barada is one of our diving pioneers, and well versed in diving physics. He stated,

Air consumption increases in proportion to the depth and exertion...

He was talking about the consumption of air from the tank. So with the same breathing rate and lung volume, I would consume twice as much air at 33 feet (10 meters) as on the surface from my 71.32 cubic foot tank, and that tank would last half as long. Similarly, at 66 feet (20 meters depth) my tank would last 1/3 as much as at the surface, and at 99 feet (30 meters) depth, 1/4 as much. Because of the density (4x on the surface at 99 feet (30 meters)), the regulator would not perform the same as on the surface either. This is what Bill Barada was talking about, and I'm pretty sure you already know this.

Concerning the Korean divers being fed off one Mk 25 first stage, think of the volume in the lines. It doesn't see that it would be hard to keep the air pressure in the lines with that amount of lines available for volume. I think any of the later, balanced first stages could do it (Calypso, MR-12, etc.).

SeaRat

 

[Nemrod]

Yes, you would use more air at depth because the density increases, not the volume . You are saying the same thing I am saying. But the excerpt is not. A regulator that can supply X volume at the surface will still do just fine delivering that same X volume at depth whether it be inexpensive or otherwise. Of course, in those days there were regulators that were inadequate on the surface and would have been equally inadequate at depth but that would be rare today, perhaps that was what he was referring or inferring.

"An inexpensive regulator, adequate for shallow water sport diving, is often incapable of delivering the amount of air required by a diver working in comparatively deep water."

I am reading "amount" as volume as that seems to be the inference. And that statement is really, well, wrong. The regulator will be able to deliver the same volume at depth. We would need to go a lot deeper than sport diving depths for the density increase to dramatically decrease flow and volume.

James

 

[Luis H]

The confusion, I think, comes from the way we (mostly here in the US) talk about the amount of air or gas in a pressure vessel. It would be more precise to refer to the amount of mass of the gas in a cylinder, but instead we talk about the amount of volume (72 cuft or 80 cuft) in the cylinder. We all know that is not the actual volume in the cylinder. That is the volume that the gas would occupy when it is released back to one atmosphere (at STP, Standard Temperature and Pressure).

We often take so many short cuts in our daily communication that they are often not precise. We also sometimes use references that tend to be misleading. We always tend to normalize gas measurements as they would be at one atm (and STP).

This is one of those cases where I think the European standards of measuring the gas in a cylinder is more direct. They refer to the actual volume inside a cylinder (7 liter, 11 liter cylinder ect.). Then all they need to do is multiply the pressure in Bars to get the amount of gas they are compressing into the cylinder. Now, to be fair they are still only talking about the equivalent gas volume as it would be measured at STP (Standard Temperature and Pressure).


I don't know if this helps...

 

[Luis H]

Here is the link to the:

SCUBAPRO record 135 divers breathing from 1 first stage​

The accumulator volume created by all the hose volume would help create a steady-state flow condition, but they would already have a steady-state (constant flow) condition with 135 divers. There is no way the divers could all inhale at the same time. The randomness of divers breathing cycle will create an almost certain steady flow. Some divers will be exhaling while some others inhaling, creating an almost constant flow. The accumulated gas in the hoses would just help a little to smooth it out, but probably very little.

The test lasted over 10 minutes. Therefore, they totally establish a steady state condition. The first stage never closed or cycled during those 10 minutes.

The question is: assuming that each diver in a rested condition breaths an average minimum of about 0.5 cfm, how many first stages can deliver at least 67 cfm (of air at STP). A simple test is how many first stages can empty a single cylinder in about one minute or less?

I have tested my Argonaut, but I can't remember the numbers. I think it would be close for a diaphragm first stage, but I think that most balanced piston first stages should be able to keep up with that kind of flow.

The catch is that that flow could be a lot higher with a lot of beginner divers.

It would have been very interesting to see an IP gauge at the regulator and maybe at some point downstream.

It is interesting that they had approximately 65,000 liters (2300 cu ft) of air available in storage cylinders. I wonder how much of it they actually used.

Lets assume they are fairly shallow (about 6.6 ft or 0.2 atm). I just notice they are all standing on the bottom so it is a shallow pool, maybe 3 feet or 0.1 atm.

For air consumption lets just say about 1 cfm average (probably a bit lower). They did one 5 minute test (125 divers) and a 10 minute test with 135 divers. That adds up to almost 2000 cu ft, not counting the gas needed for setup time (they all didn't go down at exactly the same time).

Interesting.

 

[elan]

[HIJACK]
@Nemrod , if you are impressed by the G250, you owe it to yourself to try a D400. I have a Balanced Adjustable (purchased new in 1987), a G250 (1988), and a D400 (1994). For recreational exposures in temperate or tropical water, the D400 wins, no contest, IMHO!

r7diver
[/HIJACK]

So true. I have D400 on one of my stage regs and G260, G250V on the others, A700 on the primary backgas. So I ifteb have a chance to switch between them on the same dive. G260/G250v/A700 switch is un perceivable. Going onto D400 feels like you are not breathing from a reg . Going back from D400 to the rest feels like the regs are too hard to breath

 

[John C. Ratliff]

James,

Just so you'll know, here is another diagram from "Let's Go Diving," this one in the physics area of the booklet. Titled "Boyle's Law of Air Volume and Density," it shows that Bill Barada had a very good knowledge of the relationship between air volumes and density. I point out that on the right he shows a "Skin Diver with Scuba," who has no change in lung volume. He also shows that the density changes, just as you talk about above. In the other diaphragm, he was clearly telling people that the air consumption referred to the amount of gas from the scuba tank.

Now, about regulators and volumes, at that time I remember that U.S. Divers Company (U.S.D.) was marketing the Calypso regulator as one which will satisfy the diver's demands for air at depth, verses the tilt valves which cannot deliver that amount of air (volume?) at depth under stressful conditions. U.S.D. pointed out that their downstream regulators were coming into the second stage flat (no angle) whereas the tilt valve regulators were coming in at an angle (Healthways Scubair, Scuba Star, and older U.S.D. cheaper regulators too).

I also remember that Dick Anderson from Healthways took his Scubair to depth, and wasn't satisfied with the performance, so Healthways re-designed their regulators to incorporate a downstream valve (one which did come in at an angle too).

Around 1960, Healthways started an R & D department with Gustov at the head; I was an engineer...I could no longer ignore the fact that the venturi-assisted Calypso breathed just as easy at 250 feet as at the surface. A tilt valve in the second stage couldn't cut it...

"...One day I decided to try aiming the demand valve orifice at the mouthpiece tube, so some of the air so some of the air deflected into the tube creating breath-assisting venturi...The next day I dropped down to 250 feet with Gustov. ...My prototype (was) not quite so smooth breathing as the Calypso but on a scale of 100 mine was about a 97, the tilt valve was 2 or 3. I was the happiest S.O.B. in the world..."

Diving Pioneers: An Oral History of Diving in America​

By Eric Hanauer

Diving Pioneers

This is the saga of diving in America, told by the men and women who lived it and made it. These stories and more recall scuba's pioneer days of the 40s and 50s where every dive was an adventure.

books.google.com

 

[tbone1004]

@Luis H The Poseidon MK3 is rated for 194cfm vs the MK25 rated at 301