"Real" Thirds.

[ianr33]

I fill my tanks to 3600 psi. Go dive a cave. Turn the dive when the pressure reaches 2400 psi. Exit using exactly the same amount of gas.

What pressure do I have at the end of the dive?

 

[LeadTurn_SD]

Ohhh, I suspect a trick question, but I'll bite.

You've used 1,200 psi in, turned, used 1,200 psi out, and immediately surfaced. 1,200 psi remain.

Soooo, you can now "spring the trap" on the trick question

Best wishes.

 

[ianr33]

Soooo, you can now "spring the trap" on the trick question

Best wishes.

My Pleasure

At 3600 psi air/nitrox is no longer behaving as an ideal gas. The exiting pressure will be more than 1200 psi but I don't know how much more.

Hoping someone here has the answer before I look up the Van der Waals gas equation.

 

[LeadTurn_SD]

My Pleasure

At 3600 psi air/nitrox is no longer behaving as an ideal gas. The exiting pressure will be more than 1200 psi but I don't know how much more.

Hoping someone here has the answer before I look up the Van der Waals gas equation.

I'm lucky if I can walk and chew gum at the same time.... And college was many years (and many beers ) in the past for me...... Someone far smarter than I will need to answer.

Or, you could just look at the spg when you surfaced....

Best wishes.

 

[sea2summit]

Damn, I know I read somewhere the math for how that works. It's been a while but there was a thread maybe on TDS about diminishing returns at high pressure etc. i.e. pump 95's up to 3600 and instead of getting 140cft you where getting like 120-something.

 

[willgr1]

are you doing deco on back gas?

 

[Van Isle]

I guess it depends on if the "air" used to make the mix was "Nitrox-ready."

But probably 42.

 

[ianr33]

No deco involved. Lets suppose its 20 feet deep in Mexico.
Its really a Physics question rather than a diving one.

 

[hudson]

I just played with a Van der Waals Nitrox Blender, and looks like at 2400psi and less you actually end up with more cuft than calculated (about 103%) while at 3600psi the opposite is true (about 98%). So I calculated roughly 1350 psi exit pressure, if I used the same amount on entry and exit. Nice to know (assuming it's true) - little extra safety margin there, and definitely important for blending.

 

[Jax]

So you would plug the equation from Van der Waals and Nitrox into a calculator or spreadsheet and play with the numbers for the optimal fill?