Indirect OOA question

[shark_tamer]

I have spend the last half hour reading the thread originally started by hamsiss on " Balanced second stage "

.... just one thing comes to mind " WOW, you guys are great " !!!

While reading, one question came to mind :

I have just bought a new set of 1st stage / reg / octo ( Oceanic FDX-10 DVT / Delta 4 / Alpha 8 ) and still have to go try them in the pool for the first time .

When I was at my LDS, one point came up while discussing with the attendant: So far, I've only been diving with rental regs, and I was telling him about my 2 experiences with OOA, I told him that those 2 times when I nearly ran out of air, at roughly 20bars, I felt a restriction inhaling and felt like I had about 3 or 4 breaths left in the tank before it ran dry.

The attendant told me that with a better quality 1st stage / reg, I will not get that sensation and will immediatly go dry !!!

I can see everybody answering me " That should be a good reason for you to keep a closer eye on your console !!! " , but I think this " lacking " in the lesser quality reg maybe a " plus ", and is it related to the difference between mecanically and pneumaticaly balanced regs.

I am picking your brains on that .....

 

[Dive Right In Scuba]

To be honest with you.......like you said, watch your guages more. Im not trying to be cliche, but save you life! This might not be the answer your looking for, but its a good one.

I do understand what your saying, but still, when you dive there is a right way to do things and the other way......Pay strict attention to your training and learn to do things the right way and not rely on the way a reg breathes as your indicator.

Mike

 

[The Kraken]

Shark Tamer,

I must echo DRIS here in that you should never get to the point in a dive that you know that you are low on gas because your reg is breathing harder. In a word, that is dangerous.

An old adage from my flying years, "Trust your instruments" and "Maintain a constant cross check."

Kept me alive for a while . . . albeit some of the members nowadays think my brain is dead.

the K

 

[shark_tamer]

What did I tell you !!!!

I don't remembre exactly how it happened the first time, but the last time it went like that.

The dive was over. the instructor gave the " How much air left in your tank " signal.
I answered with the 50 bars fist signal.

He then signaled the group that the dive was over and that we where to start our ascent. At that time the depth was 15 meters .

Since I am a photographer, I spotted some marine life not too far and proceeded to chase it ( I have now learned not to chase marine life but to let them come to me ), and I went thru 30 bars in an instant ....

I do keep a close eye on my console and everybody that I dove with so far, tell me that I am a very safe diver !!!

 

[spectrum]

If that's the way you intend to dive I suggest stocking up on J valves. Seriously running the tank down twice in inder 50 dives is inexcusable for you and as your buddies buddy.

There have been some regulators and valves in the past that made a audible alarm when passing a preset pressure like 500 PSI.

Pete

 

[SharkDZ]

If that's the way you intend to dive I suggest stocking up on J valves. Seriously running the tank down twice in inder 50 dives is inexcusable for you and as your buddies buddy.

There have been some regulators and valves in the past that made a audible alarm when passing a preset pressure like 500 PSI.

Pete

Sounds like a good case for an air integrated computer with audible alarm.

 

[Diver0001]

I have spend the last half hour reading the thread originally started by hamsiss on " Balanced second stage "

.... just one thing comes to mind " WOW, you guys are great " !!!

While reading, one question came to mind :

I have just bought a new set of 1st stage / reg / octo ( Oceanic FDX-10 DVT / Delta 4 / Alpha 8 ) and still have to go try them in the pool for the first time .

When I was at my LDS, one point came up while discussing with the attendant: So far, I've only been diving with rental regs, and I was telling him about my 2 experiences with OOA, I told him that those 2 times when I nearly ran out of air, at roughly 20bars, I felt a restriction inhaling and felt like I had about 3 or 4 breaths left in the tank before it ran dry.

The attendant told me that with a better quality 1st stage / reg, I will not get that sensation and will immediatly go dry !!!

I can see everybody answering me " That should be a good reason for you to keep a closer eye on your console !!! " , but I think this " lacking " in the lesser quality reg maybe a " plus ", and is it related to the difference between mecanically and pneumaticaly balanced regs.

I am picking your brains on that .....

I did a live experiment a few years ago to test this idea that newer regs would give you less warning. Here are the results:

Using a 15 litre tank with a Y valve on it. On one side I mounted a Sherwood Maximus (balanced piston) manufactured in 1998-99 and on the other side I used a AuqaLung Aquarius (unbalanced piston) manufactured in 1972, which, for some reason I can't bring myself to throw/give away...

Started breathing at 30 bar (435psi). Pressure measured with the AI computer I had at the time withresolution of 0.5bar (7 psi). The test was done on the surface, so the numbers you see here will be higher as you go deeper.

Breathing down to 10 bar, there was no change in the performance of either reg.

At 8 bar (116psi) the unbalanced reg starts to get heavy. The balanced reg is
still breathing like it does with the tank full.

At 5 (72psi) bar the unbalanced reg is getting progressively heavier. The
balanced reg is showing no decrease in performance.

At 2 (29psi) bar. No change as compared to 5 bar

At 1 bar (15psi). No change

At 0.5 bar (7.something psi). the unbalanced reg is heavy but it is still
possible to breathe more or less normally. The balanced reg is *still* showing
no decrease in performance.

Gauges jump to 0.0. Both regulators are still breathing. The unbalanced reg is
heavy but possible. The balanced reg is still showing no deterioration in
performance as compared to a full bottle.

Now we count breaths.

10 breaths. Even the balanced reg is starting to show signs of protest.

20 breaths. The unbalanced reg becomes unusable.

30 breaths. The balanced reg is getting heavy

40 breaths. The tanks is completely empty. The balanced reg gives air until
the last. Pressure in the tank is now so low that you can blow air back into
the tank via the open valve.

Time 4 minutes 40 seconds from the moment the gauge turned to 0.0.

What I concluded was:

- a balanced reg won't seriously deteriorate in performance until your gauges show more or less zero.

- An unbalanced reg will give you a bit of warning, showing significant performance degradation from 8 bar,

- but even an unbalanced reg will continue to function until the gauges read zero.

- A balanced reg gives you a couple more breaths as the tank pressure reaches zero.

- Neither reg cut out suddenly. They both showed performance decreases as the end drew near. (this is a key result)

- Zero didn't really mean zero on my computer. Probably everything needs to be padded up a bit

R..

 

[The Chairman]

You should ALWAYS know your pressure as well as your buddy's air pressure. Your buddy should know both as well. This is the BEST scenario for not running out of air. I also like the audible alarms for those who are determined to NOT look at their gauges.

My first set of gear had a j-valve with no SPG. Every dive was ended by someone running out of air and heading for the surface. Sometimes our reserve valve was already opened when the regs stopped breathing. I simply don't remember it getting that hard except for the last breath or so.

 

[CD_in_Chitown]

....Pressure in the tank is now so low that you can blow air back into the tank via the open valve.

As if the risk of aspirating water isn't convincing enough, reason #2 involves that pressure drop and the threat of ambient forcing water up through your regs and into your tank. Something you want to avoid like the plague, or like running out of air, when you own the gear. Saves you a dime or two in the maintenance department, prolongs your kit's life.

 

[divemaster_jim]

I did a live experiment a few years ago to test this idea that newer regs would give you less warning. Here are the results:

Using a 15 litre tank with a Y valve on it. On one side I mounted a Sherwood Maximus (balanced piston) manufactured in 1998-99 and on the other side I used a AuqaLung Aquarius (unbalanced piston) manufactured in 1972, which, for some reason I can't bring myself to throw/give away...

Started breathing at 30 bar (435psi). Pressure measured with the AI computer I had at the time withresolution of 0.5bar (7 psi). The test was done on the surface, so the numbers you see here will be higher as you go deeper.

Breathing down to 10 bar, there was no change in the performance of either reg.

At 8 bar (116psi) the unbalanced reg starts to get heavy. The balanced reg is
still breathing like it does with the tank full.

At 5 (72psi) bar the unbalanced reg is getting progressively heavier. The
balanced reg is showing no decrease in performance.

At 2 (29psi) bar. No change as compared to 5 bar

At 1 bar (15psi). No change

At 0.5 bar (7.something psi). the unbalanced reg is heavy but it is still
possible to breathe more or less normally. The balanced reg is *still* showing
no decrease in performance.

Gauges jump to 0.0. Both regulators are still breathing. The unbalanced reg is
heavy but possible. The balanced reg is still showing no deterioration in
performance as compared to a full bottle.

Now we count breaths.

10 breaths. Even the balanced reg is starting to show signs of protest.

20 breaths. The unbalanced reg becomes unusable.

30 breaths. The balanced reg is getting heavy

40 breaths. The tanks is completely empty. The balanced reg gives air until
the last. Pressure in the tank is now so low that you can blow air back into
the tank via the open valve.

Time 4 minutes 40 seconds from the moment the gauge turned to 0.0.

What I concluded was:

- a balanced reg won't seriously deteriorate in performance until your gauges show more or less zero.

- An unbalanced reg will give you a bit of warning, showing significant performance degradation from 8 bar,

- but even an unbalanced reg will continue to function until the gauges read zero.

- A balanced reg gives you a couple more breaths as the tank pressure reaches zero.

- Neither reg cut out suddenly. They both showed performance decreases as the end drew near. (this is a key result)

- Zero didn't really mean zero on my computer. Probably everything needs to be padded up a bit

R..

Interesting experiment, But I wouldn't use that as a base for every unbalanced 1st stage, I mean some will cut-off completely when taken down that low. Have you tried to find that point on your unbalnanced one yet? As far as I know the Aquarius won't lock up til the tanks bone dry, If I remember right isn't a saucer shaped 1st stage?