Diving "Modern" with "Vintage" Reg

[pescador775]

Bill Barada was one of the godfathers of diving, highly respected in the community. However, as to the above drawings, that was then. Bill, basing his drawings on a similar analysis published by US Divers, was partially correct but missed the relationship between the relative position of the double hose mouthpiece, the regulator diaphragm and breathing resistance. The effect of this is that a diver in vertical position experiences easier breathing than in inverted position. Cousteau's first Gagnan regulator had one hose with the exhaust port positioned at the mouthpiece. Results were not good. His seminal invention was to route the exhaust side all the way back behind the diver's head to the regulator diaphragm. This open circuit loop referred to as "double hose" prevented the free flow which had plagued his earliest tests but did not change the physics, only adapted to it; thus, gauge pressure at the mouthpiece still varies with the position of the mouthpiece relative to the diaphragm. As was said in prior posts, this is actually an advantage in some situations. At worst, the diver may find that inhalation/exhalation efforts vary with position. This is not a big deal when challenged by an environment with so many distractions and tasks as to render the slight variations in breathing unnoticeable. Rather, the extraordinary fact that breathing underwater is even possible with such a simple device always seems to filter into the back door of the conscious mind.

 

[Creed]

Well, I just got my Healthways back from the machine shop. Just by positioning the levers at a 90 degree angle to the inhaltion port, I got a noticeable increase in performance. It now breathes at about the same level as the DA I had Bryan from VDH rebuild and tune for me. I've got two more changes I am going to make, but this is an example of a simple change that can enhance the performance of a regulator. I think with a silicon diaphram along with the other changes I have in mind, I could make this reg into a seriously nice breather.

 

[Nemrod]

Regarding the diagram. Notice in the top left corner that diagram shows the most normal swimming position and shows the double hose at a disadvantage--BUT--that is misleading because even using a BP/wing, most people including me swim with a slight downward tilt to their body and their head and neck are tilted upward so as to see where you are going. In this NORMAL swimming position the dh regulator suffers no serious disadvantage and performs well. Many of us have learned to imperceptably roll to the favored side thus further improving the breathing. Roll to the side--how--it is simple and requires no thought if your truly 3-D--but--it is not required--a normal swimming position as any diver with good trim and good bouyancy skills seeks to obtain is quite good for the dh regulator. No special tricks or concentration are required. N

 

[Luis H]

Cousteau and Gagnan found that the exhaust needs to be next to the demand valve sensor (the diaphragm) to avoid a differential pressure due to the water column and therefore a potential free flow. That is why they added the exhaust hose to close the loop.

When you remove the mouthpiece from your mouth you in essence open the loop again. But when the mouthpiece is in your mouth the loop is close and the position of the mouthpiece is irrelevant. The respiratory driving muscles are not in your mouth, they are around your lung. The air routing in the hoses, the mouthpiece, your trachea, etc is irrelevant. As long as the loop is closed the two locations of importance in the water column are the demand valve sensor (again the diaphragm) and the lungs.

The only time the position of the mouthpiece in the water column really maters is when you put the demand valve diaphragm there (as in a single hose regulator).

The ideal place to put the demand valve sensor is as close to your lungs as possible. Cousteau and his team often used a chest mounted regulator. In his later years that was the best way for JYC to be able to dive. Ryan Spence has a great picture of JYC wearing a Spirotechnique Mistral on his chest, but I can’t find it to re-post it here.


Since we cannot mount the demand valve sensor in the lungs, the next best thing would have been the zero differential pressure suit. I have mentioned about the development of it in other threads (and other message boards). The suit was intended for long term exposure divers (commercial and military). A very basic description is a flexible suit that uniformly squeezed you to a pressure a few inches of water lower than the lowest point in you exposed water column. The position of the demand valve sensor is not critical since it was biased to provide a constant positive pressure. The exhaust was also biased (restricted) to close the loop and only exhaust at above the suit pressure.

In practice the zero differential pressure suit turned out to be a bit more complicated than it was worth.

In theory it is possible to biased the demand valve and the exhaust to work at a few (2 to 3 in WC) inches of Water Column higher (positive pressure) than ambient without the suit or hurting you lungs, but the moment you take the mouthpiece of you mouth it will free flow (even out of the water) unless there was a shut off in the mouthpiece (like a re-breather). In some positions (I believe) this could increase the chance of an air embolism to some people (I am not a doctor; I am only an engineer and an EMT).

 

[pescador775]

When you remove the mouthpiece from your mouth you in essence open the loop again. But when the mouthpiece is in your mouth the loop is close and the position of the mouthpiece is irrelevant. The respiratory driving muscles are not in your mouth, they are around your lung. The air routing in the hoses, the mouthpiece, your trachea, etc is irrelevant. As long as the loop is closed the two locations of importance in the water column are the demand valve sensor (again the diaphragm) and the lungs.

If the position of the mouthpiece were irrelevant, no major difference in inhalation effort would occur when the diver goes from vertical to inverted. However, these differences occur and are mainly due to the mouthpiece position. When the diver is vertical the mouthpiece is higher than the regulator diaphragm. The absolute pressure in the hose is always at the level determined by the diaphragm and it is the same along the entire length of the loop. However, the gauge pressure in the hose is infinitely variable along the length of the hose, and highest at the mouthpiece when the diver is vertical. This is due to the fact that the ambient pressure at that point is lower than that to which the regulator diaphragm is subjected. This causes a "positive pressure" effect at the mouthpiece and provides substantial assistance to the human diaphragm (which is located below the lungs) when the diver is vertical or facing upward. This effect can visibly cause the diver's cheeks to puff out a bit. Fortunately, the pressure differential is only about six inches of water column, not enough to bulge the hose. However, a loose mouthpiece could easily leak or even blow off so good maintenance is advisable.

 

[captain]

If the position of the mouthpiece were irrelevant, no major difference in inhalation effort would occur when the diver goes from vertical to inverted. However, these differences occur and are mainly due to the mouthpiece position. When the diver is vertical the mouthpiece is higher than the regulator diaphragm. The absolute pressure in the hose is always at the level determined by the diaphragm and it is the same along the entire length of the loop. However, the gauge pressure in the hose is infinitely variable along the length of the hose, and highest at the mouthpiece when the diver is vertical. This is due to the fact that the ambient pressure at that point is lower than that to which the regulator diaphragm is subjected. This causes a "positive pressure" effect at the mouthpiece and provides substantial assistance to the human diaphragm (which is located below the lungs) when the diver is vertical or facing upward. This effect can visibly cause the diver's cheeks to puff out a bit. Fortunately, the pressure differential is only about six inches of water column, not enough to bulge the hose. However, a loose mouthpiece could easily leak or even blow off so good maintenance is advisable.

I believe this to be true and is proven by the single hose regulator. With a single hose breathing effort is almost the same no matter what the relationship of the lungs to the diaphragm. The reason it doesn't change is because of the close relationship of the diaphragm to the mouth piece.

 

[pescador775]

Captain, I understand you acquired a Voit Scuba set in 1957 at age 13. My guess is that set cost about $160 which was a fortune in those days. My first Scuba was a war surplus rig which I built up from stolen parts (derelict B29 bomber, nobody cared) and first used in 1954. My first commercially mfgd set was a Divair which was in use from 1956. I worked odd jobs and saved my lunch money for a year to get it. God knows what I would have done to obtain a real two stage, top line outfit like the Voit. The opportunity didn't present and that is just as well. You must have had some generous parents or whatever. The original war surplus rig consisted of two 38 cf bottles filled with Aviators Breathing Oxygen. I made my first ever Scuba dive in a local swimming spot called "mules hole". When entering the water, there was no one else around as the place was overgrown and not visited by many anymore. I made my way down to a depth of 25 feet and saw some fish which gave me the idea to start work on a pole spear the next day. Meanwhile, the dive went well but visibility became a little cloudy from my excited jetting around but I didn't get an embolism or anything like that. It was fun. I ascended slowly at first then broke the surface with a "wooosh". Two Negro boys who were sitting on the bank dropped their cane poles and sprinted for the woods. No amount of calling would fetch them back. I then remembered that was the year of "Creature from the Black Lagoon".

 

[pescador775]

The single hose regulator's performance is fairly easy to understand in light of the relationship of the regulator mouthpiece/diaphragm to the lungs. That is, a vertical diver will experience only slightly greater breathing resistance and this is entirely due to the relationship of the regulator which is at lower pressure than the lungs. Also, the reverse is true for the inverted position. Since there are no low pressure hoses in the circuit, this complicating factor does not enter into the discussion. Analysis of the single hose is a useful starting point and perhaps suggests how much extra force is added or subtracted to cracking effort due to these positioning variables alone. It hints at the relative values which may be attributed to variable positioning of the two hose regulator and how much weight to assign to this versus the competing or complementary pressures at the mouthpiece. I suppose the two hose variables could be calculated and just leave the single hose out of the discussion. The physics are relatively simple, but why bother?

 

[pescador775]

Creed, I don't recall much about the Healthways reg. Did you rotate the main casting so as to allow direct injection into the inlet hose? Were the levers baffling the flow into the hose?

About maintenance of the two hose. I've never had to do much in the way of repairs or service. Use of silicone mushroom valves eliminates the curling and stiffening which allow water to bypass neoprene valves. Using these, I've not had problems with water entering the box, not for many years. The RAAM seems to last forever. The only maintenance I've done to my primary reg over three decades is replace the little O ring in the balance chamber with Viton, replace the duck bill a few times, replace the hoses once or twice and replace the inlet filter. Oh yes, to anticipate possible oxygen service, I replaced the high pressure poppet with one which has a synthetic seat.

 

[Luis H]

I have not tried this yet myself, but if you can locate the demand valve at the same level as your human diaphragm (or a bit above it at the lower lung location) you are not supposed to notice any difference whether you are vertically facing up or facing down. The best way to accomplish this is to wear a double hose regulator low on your chest like JYC and the Calypso divers used to wear them.

That being said, as humans we are the worst measuring device we could come up with. Without instrumentations our perception is often influenced by many factors that we are not capable of isolating.

pescador
You are correct in that the entire air loop is at a constant pressure (since air can be considered weightless under these short vertical distances). Therefore, you are also correct in that the differential pressure (I think you are calling it gauge pressure) from any point inside the air hose to a corresponding horizontal point outside of the hose is going to change as the pressure on the water column changes due to the weight of water. For flow calculations we often use inches of water column as a unit of pressure (1 in WC = 0.0361 PSI).

The physics behind a flow analysis in a hose, pipe, or duct, etc is fairly straight forward. The actual path of a submerge air hose (or a water hose in air) doesn’t affect the flow (the length does), only the beginning and final elevation points are important. On the other hand I am assuming the human trachea behaves like a simple air duct, but I am not qualified to confirm that assumption. I don’t believe that we have auxiliary breathing muscles around our trachea or anywhere else in our wind pipe, but I am an amateur when it comes to knowledge of human physiology.

In reference to the breathing resistance of a single hose as a function of position, I can tell the breathing resistance difference at different positions. When I am vertical it is harder to breath, specially if I look up (even with my well tuned Poseidon regulator). But, as I mentioned above, as a human I am not a well calibrated instrument.