Hog D1, updside down breathing is difficult

[kelemvor]

Well, there is a considerable difference between my r295 and my s600 upside down. In shallow water, not inverted, they feel about the same. I guess it must be a difference in tuning that's not discernible under normal conditions.

Also, if this is right, they can all perform well inverted when properly tuned.

 

[BRT]

which has been my point the whole time about breathing upside-down. You have to inhale against the pressure differential instead of with it when the diaphragm is up. WoB does not change with body orientation, only with diaphragm orientation because WoB is the area under the curve of BOTH inhalation and exhalation. The ideal scenario is you are head down when you inhale and head up when you exhale to minimize WoB, but if you are at 20* down, the inhalation is easier than the exhalation by roughly the same amount that it is harder if you are 20* up. That is not the discussion, the discussion is regulator orientation due to the diver rolling on his/her back. You proved my point with your last sentence

Define the pressure differential. Between where and where?

 

[tbone1004]

when the diaphragm is up, you have to create a negative pressure inside of the case equivalent to the spring pressure + the pressure differential between the air in the case and the water. This is ambient pressure obviously but gravity still exists so you have to fight the air trying to rise. This is a positive number and is noticeable, even when your lungs are above the body of the regulator.
When the diaphragm is down you have to inhale against the spring pressure + the pressure differential between the air in the case and the water on the other side of the diaphragm. The second scenario actually creates a negative value when the regulator is tuned properly due to the venturi.

I.e. if you take a magnehelic gauge and put it on a regulator and put it in the water, it will read a zero or slightly negative value on a well tuned regulator if the diaphragm is down, and a positive value that is larger than the value that you tuned the reg to when it was tested in air when the diaphragm is up.

 

[cerich]

when upside down the exhaust valve also lets in water when you exhale much more than when up side right, and the mouthpiece is the lowest point, so gravity moves that extra water there where you notice it. That is why you find it wetter

To the harder breathing physics and physiology getting together.

 

[BRT]

when the diaphragm is up, you have to create a negative pressure inside of the case equivalent to the spring pressure + the pressure differential between the air in the case and the water. This is ambient pressure obviously but gravity still exists so you have to fight the air trying to rise. This is a positive number and is noticeable, even when your lungs are above the body of the regulator.
When the diaphragm is down you have to inhale against the spring pressure + the pressure differential between the air in the case and the water on the other side of the diaphragm. The second scenario actually creates a negative value when the regulator is tuned properly due to the venturi.

I.e. if you take a magnehelic gauge and put it on a regulator and put it in the water, it will read a zero or slightly negative value on a well tuned regulator if the diaphragm is down, and a positive value that is larger than the value that you tuned the reg to when it was tested in air when the diaphragm is up.

Negative or positive magnehelic gauge pressure in relation to what pressure?

 

[tbone1004]

the pressure that you set the regulator to in the air

 

[BRT]

the pressure that you set the regulator to in the air

I promise you that at any depth in water the pressure inside the regulator will be higher than what you set it to in air. I may not understand what you are saying here but the pressure on the diaphragm is the same at the same depth whether the reg is pointed up or down.

 

[tbone1004]

the OP is complaining about a perceived cracking pressure increase when breathing upside-down. Regulators experience different cracking pressures depending on the diaphragms orientation in the water. This is obviously not the case when the regulator is in air, so magnehelic gauges can be used to set cracking pressure regardless of orientation. If you put a mag gauge on a regulator and try inhaling at different orientations while in the water, you will experience a much higher cracking pressure when the diaphragm is up, than it is when the diaphragm is down.

 

[halocline]

This is an often-debated point; if you search you'll find lots of threads about it. Some very knowledgeable people, (Luis in particular) argue that it is the difference in average lung depth and regulator depth that determines cracking effort. Personally I believe that geometry in the 2nd stage case has more to do with it, but it's not about the orientation of the diaphragm. I know this for a fact because the D series and earlier SP center-balanced valve 2nd stages have the diaphragm orientation reversed and yet they act almost exactly the same in the water.

I think that the relative depth between the diaphragm/lever contact point and the exit of the mouthpiece is very important in cracking effort. In most 2nd stages, there's at least a 1" difference between these two points; face down, the mouthpiece is shallower; face up, it's deeper. So that would account for 2" overall difference between these two positions. 2" is a lot of cracking effort.

If you've ever used a double hose regulator, you know that moving the mouthpiece up to a shallower depth than the can (which is the 2nd stage) causes it to freeflow, moving it deeper causes cracking effort to increase sharply. The orientation of both the mouthpiece and the can relative to the surface makes no difference in this behavior.

Since the exit of the mouthpiece and the lungs are all part of the same breathing loop, I'm willing to concede that lung depth has some influence over WOB, but certainly not entirely. Try breathing on a conventional 2nd stage while vertical in the water, head towards the surface but looking parallel to the surface, then try up-side down, feet towards the surface but still looking horizontally. There is some difference in cracking effort, but not nearly as much as the face down/face up comparison. Yet, feet up/feet down represents by far the biggest difference in lung/regulator depth.

 

[Bryan@Vintage Double Hose]

See attached photo