Reg breathes hard when swimming upside. Solutions?

[randyjoy]

there will also be less pressure on the seat during storage with the lighter adjustment and an excessive seating groove will take a lot longer to devleop.

Atomic's have a spring that pushes the orifice away from the seat when the second stage is unpressurized, so there should be no pressure on the seat during storage.

 

[halocline]

Thanks DA, you've mentioned case geometry fault before but now I feel like I understand it better. I've never believed that the difference in breathing is primarily due to pressure differential between lungs and 2nd stage for the simple reason that breathing resistance in an upright (vertical) position is roughly the same as breathing resistance when upside down; those two positions present the greatest difference in lung/reg depth positions, so if that were the primary factor, there would be the greatest difference in breathing in those two positions.

 

[ba_hiker]

Well, the pressure of the air inside the airbox of your regulator and the pressure of the water on the outside is the same, so I would discount the "air bubble" theory. It truely is the different water pressure against the lungs vs the diaphragm. this can be seen clearly with a tub of water and a charged regulator. Thanks.

Phil Ellis

If this were the case, then when vertical in the water (head up and feet down) the breathing would be even harder, as the height difference would be at the maximum. There is no position where the regulator would be higher with regard to the lungs.

 

[mobeeno]

Oh no.....it's this topic once again. Despite a few good samaritans' attempts at convincing me that the depth differential is the reason, I remain pretty confident that it has more to do with the diaphraghm's orientation to the surface. Hence the reg which freeflows when mouthpiece up, stops when mouthpiece down. There is air on one side of the diaphraghm and water on the other, so...I guess I'm kind of like those guys that thought the world was flat.

Anyhow, there is a practical solution; I have a friend who recently bought a D400 and the effect of breathing resistance increasing when looking at the surface was greatly reduced. Hmmm....I wonder if this has anything to do with the fact the diaphragm in that reg is not parallel to the surface when you're facing up? Naw..

I use an old D350 (pre D400) for swimming on my back to enjoy panoramic views, while using a G250hp as a back up.

 

[DA Aquamaster]

It's really too bad Scubapro discontinued the D400.

Actually, it's too bad they saddled it's exceptioanl center balanced poppet with a crappy plastic orifice that made it finicky and hard to adjust and THEN discontinued it because it was finicky and hard for techs to adjust.

The D300, D350 and D400 all offered a level of subjective performance that never fully showed itself on the work of breathing charts that became so popular with the marketing types and magazine reviews. One of those subjective qualities was it's ability to deliver excellent performance in any orientation with no need for diver adjustment in the water. Another subjective quality was the smooth airflow and the very natural quality of its breathing performance. If you compared the two, the G250 was more of a muscle car while the D400 was pure Ferrari.

 

[mobeeno]

"If you compared the two, the G250 was more of a muscle car while the D400 was pure Ferrari"

I like that analogy

 

[Luis H]

mattboy

Yeap… this again.

If you had access to a double hose regulator you could prove that breathing resistance is affected by the pressure differential in the water column, not the direction the diaphragm is pointing.

Since the mouthpiece on a double hose regulator moves independently to the diaphragm, you can perform the following experiment easily:
You can sit at the bottom of a pool breathing out a double hose that you can position right in front of you. Then you can rotate the regulator (it easier if it is attached to a small tank) so the diaphragm point in any direction and you will notice that it doesn’t make any difference. On the other hand if you move the regulator up or down you will immediately notice the change in inhalation resistance.

Every inch you move the diaphragm up will increase inhalation resistance by an inch; the opposite when you move it down. I have done it and there is no question that this is how it behaves. The first and second stages in a DH regulator are mechanically the same as in a single hose (the difference is just the packaging).

Regulator inhalation resistance is measure in inches of water. The initial inhalation resistance in good performing regulator is somewhere around 1 inch. Where 1inch of water column equals 0.036 PSI. (1 inWC = 0.036 PSI is a standard engineering unit for measuring pressure).

The distance from the diaphragm to the mouthpiece (or to the exhaust valve, like DA AquaMaster mentioned) on a single hose is easily over an inch. Therefore if the mouthpiece is lower or higher than the diaphragm it will breathe different.

If you tried a Poseidon Cyklon regulator with the diaphragm pointing to the left you will also feel a difference when your mouthpiece is below or above the regulator (granted it is a lot less since the distances are smaller).



The information above is very clear to me; my background is in engineering and physics. What I don’t know is if you feel pressure near your mouth or your lungs (my knowledge of physiology and medicine is very limited). From your observation and that of several others it seems that most people sense pressure (inhalation resistance) near their mouth. Perhaps, we feel it by the throat near the Eustachian tube, just my guess. Actually that would make sense since we do feel pressure in our ears.

I have always assumed that you feel pressure at your lungs, since that is were the inhalation work seems to take place. But, I am starting to think that the important pressure sensors (primary sensors that measure inhalation suction) are much closer to the mouth or throat. It would be great if someone with a medical background could confirm if this is true.



I don’t mean to highjack the thread, but it seams that the OP already has his answer.

 

[hamsiss]

DA,
Can you say the same things(D400's advantages esp. its geometry and dryness) about X650, if not why?

 

[DA Aquamaster]

DA,
Can you say the same things(D400's advantages esp. its geometry and dryness) about X650, if not why?

The X650 was marketed as a replacement for the D400 and SP essentially claimed to have incorporated the key D400 features with an easy to service and adjust S600 styled poppet assembly.

The poppet assembly is indeed a lot more S600 like and is essentially identical except it uses a shorter version of the S-wing poppet used in all of SP's other balanced regulators. So the poppet is fine and the locaton of the poppet allows smoother air flow as it is right in front of the mouthpiece (like in the D400) and does not have to make the bank shot that occurs with conventional second stage regulators where the air enters the second stage below the mouthpiece.

But the good news stops there. The X650 does incorporate a case that looks sort of like the D400 and incorporates a diaphragm that is angled downward about 45 degrees. However the engineers who designed it either did so only to create the sort of D400 look or they were morons who had no clue about Case Geometry Fault (CGF) and basic physics that affect the second stage underwater.

The purpose of the 45 degree angled diaphragm on the D400 was to cause the worst case CGF issues to occur in orientations divers were seldom in AND to create no CGF issue at all in the normal swimming position where the diver spends most of his or her time. Plus, the reason why the D400 had virtually no negative impact on inhalation effort due to case geometry faulty was because of the coaxial diaphragm and exhaust valve limited the maximum distance between the diaphragm center point and the "top" edge of the exhaust valve to .5 inch, and in the nmormal swimming position this vertical distance was .0 inch.

Unfortunately the angled diaphragm accomplishes absolutely nothing on the X650 as it does not incorporate the coaxial exhaust valve. The exhaust valve is located in a conventional location at the bottom/rear of the X650's case. What this means is that in a normal swimming position where the diver is looking down at a 30-45 degree angle, the top of the exhaust valve is at or very near the maximum vertical distance it can be from the center of the exhaust valve. So in essence the genius(es) that designed it created a second stage where the worst case CGF condition occurs in a normal swimming position. Absolute and total stupidity. Then as if that were not enough, they created a very large and easy to open exhaust valve that guarentees air escapes easily.

This means in a normal swiming position the regulator has to be detuned to a cracking effort of at least 1.4 inches to ensure that the diaphragm rising in the case as the air slips out the exhaust valve does not depress the demand lever and start a freeflow. At best this wastes the potential performace that you could get from what is a very good poppet design. However, the very easy breathing poppet actually works against it and in practice I have found that in order to completely elminate a slight dribble of air out the exhaust valve between breaths in a normal swimming position, I have to detune the reg to an inhalation effort around 1.8 to 2.0 inches of water.

To me, having no freeflow at all is important as in extremely cold water the cooling effect caused by even a very slight dribble of air can add up during a dive. I have found that unless I detune the reg to the 1.8 to 2.0 range it will be spitting ice chunks at me half way through an ice dive. To give it credit, I have only froze one up once at the surface in near zero weather, and it has never frozen up under water, but it makes me nervous.

Now, if the SP engineers stopped looking out their belly button windows they coud rectify the problem by redesigning the second stage to incorporate a coaxial diaphragm and exhaust valve. This would require:

1. plugging the existing exhaust valve,
2. designing a purge cover to incorporate an exhaust T (or perhaps one designed to channel the exhaust to a conventional exhaust T mounted on the back of the second stage to reduce bubble interference)
3 designing or adapting a D400 style coaxial diaphragm and exhaust valve
4. and would require a new lever to interface with the new diaphragm.

I think it would be a great design that would ionfact offer D400 performance. They could call it the X700 and retrofit most or all of the improvements into existing X650's with or even without an entirely new case depending on how they handle the exhaust issue.

But until they do that, the X650 will in no way come close to achieving D400 performance.

 

[halocline]

Hi Luis! Thanks for responding quickly and patiently. Could you answer these questions for me?

1. How do you explain that in my experience there is little or no difference in breathing resistance when I'm vertical right side up, in which case the reg is several inches above my lungs, and vertical upside down, in which case the reg is several inches below my lungs?

2. A high performance reg will often freeflow when turned mouthpiece up, and will usually stop when turned mouthpiece down. This to me is a clear indication that air flows with less resistance through a reg when the "dry side" of the diaphraghm is up. Can you explain why this ocurrs and why it would not have an impact on breathing resistance?

I'm not doubting your expertise, I'm just a curious guy. Thanks!