LP45/50s in cave diving

[Superlyte27]

I’ve generally found them happy to explain things and even happier to be correct when explaining something. That said, what pressure in an LP50 (to you) equates to 72cf of gas? We can assume say, 15°C temperatures but happy with even the usual FL springs temperature.

Pull the stick out of your butt. I was guessing at cubic footage off the cuff while sitting in the sun waiting for my student to finish building his rebreather. You get the point. Or maybe you’re too dense and you don’t. I don’t know. That’s a question you need to answer for yourself.

 

[grantctobin]

Pull the stick out of your butt. I was guessing at cubic footage off the cuff while sitting in the sun waiting for my student to finish building his rebreather. You get the point. Or maybe you’re too dense and you don’t. I don’t know. That’s a question you need to answer for yourself.

Okay, what is the cubic footage of the LP50 with 32% at 3600psi? It would appear that I do not see the point.

Fret not though, I don’t think your cave IT would have (has?) the answer either, but hopefully is a good learning point for anyone asking about using LP50s as bailout.

 

[Superlyte27]

Okay, what is the cubic footage of the LP50 with 32% at 3600psi? It would appear that I do not see the point.

Fret not though, I don’t think your cave IT would have (has?) the answer either, but hopefully is a good learning point for anyone asking about using LP50s as bailout.

Need help with that stick? I am a Cave IT, FYI.

Let me know when you have 10% of the diving experience I have.

And I’m not sure the OP asked specifically about bailout. FTR, I absolutely love LP50’s for bailout, as I brought them to the masses in about 2010. My initial order for leaders/founders of IANTD was three pallets of them.

 

[grantctobin]

Need help with that stick? I am a Cave IT, FYI.

Let me know when you have 10% of the diving experience I have.

Yes, I do need help. And yes, I’m familiar with your ITs.

I’d still like to know what the cubic footage is. With your background, I’d think it quite trivial.

 

[Superlyte27]

Yes, I do need help. And yes, I’m familiar with your ITs.

I’d still like to know what the cubic footage is. With your background, I’d think it quite trivial.

Oh it is, but so are you, find another monkey to jump for you.

 

[berndo]

So, pumped up lp50’s might be 72cu’ for each. 144cu’ total. 48cu’ of penetration at .5 sac rate with a 50fpm swim speed in 100’ of water is 600’ of penetration.

0.5 cuft as in 14 liters? That's for when the ccr craps out for the swim back? Is that normal? Sounds pretty optimistic, no?

 

[grantctobin]

Oh it is, but so are you, find another monkey to jump for you.

I don’t envy the loss you’ve experienced in your life, but this seems pretty jaded. You’re also more than welcome to insinuate the monkey-ness, but I don’t think I’ve called you that before.

For other readers, most people (including IT and ITC) are never taught gas compressibility. Linearity breaks pretty quickly after 180bar / 2640 psi or so, and it grows worse with higher concentrations of helium.

LP50 has 49.5cuft of ideal gas capacity at rated pressure of 2640psi.

3600psi (in the example Pete wishes not to answer) / 2640 rated * 2640 = 67.5. However, we do not live in an ideal world. To borrow DGX tables (as these are the easiest to reference and probably one of the better sources on the internet), at 3600psi and 15°C, the Z factor of 32% is 1.0491. Thus, we must discount the 67.5 by this compressibility and arrive at 64cf.

10/70? We must discount by 1.1529 to get to ~58.5.

Is concern with 3.5cf silly? Sure, why not. But so is assuming the average, overweight, mid forties or older cave diver can swim at 50’ per minute in a no flow cave at a 0.5 SAC rate after needing to bailout.

n.b on a pair of LP120s at 3600psi full of 10/70 goes from 3600/2640*120=163cf down to 142cf. I do care about 40cf of gas and do think most people using LP50s in a 4ATA cave are silly geese.

 

[Superlyte27]

I don’t envy the loss you’ve experienced in your life, but this seems pretty jaded. You’re also more than welcome to insinuate the monkey-ness, but I don’t think I’ve called you that before.

For other readers, most people (including IT and ITC) are never taught gas compressibility. Linearity breaks pretty quickly after 180bar / 2640 psi or so, and it grows worse with higher concentrations of helium.

LP50 has 49.5cuft of ideal gas capacity at rated pressure of 2640psi.

3600psi (in the example Pete wishes not to answer) / 2640 rated * 2640 = 67.5. However, we do not live in an ideal world. To borrow DGX tables (as these are the easiest to reference and probably one of the better sources on the internet), at 3600psi and 15°C, the Z factor of 32% is 1.0491. Thus, we must discount the 67.5 by this compressibility and arrive at 64cf.

10/70? We must discount by 1.1529 to get to ~58.5.

Is concern with 3.5cf silly? Sure, why not. But so is assuming the average, overweight, mid forties or older cave diver can swim at 50’ per minute in a no flow cave at a 0.5 SAC rate after needing to bailout.

n.b on a pair of LP120s at 3600psi full of 10/70 goes from 3600/2640*120=163cf down to 142cf. I do care about 40cf of gas and do think most people using LP50s in a 4ATA cave are silly geese.

So, A. 4000psi fills are the norm round these parts. B. 50fpm is slower than I can maintain. C. My average SAC in no flow is about .32
I honestly don’t believe I’ve ever had a cave student that couldn’t maintain 50fpm.

But, who the phuck cares? Quit being pedantic. I was cave diving when EVERYONE but the wealthy was doing Intro to Cave on a single 104. Lp50s are better than that due to true redundancy.
And D. Let me know when you have 10% of my background and experience and we’ll start caring about your perspective.

 

[grantctobin]

So, A. 4000psi fills are the norm round these parts. B. 50fpm is slower than I can maintain. C. My average SAC in no flow is about .32
I honestly don’t believe I’ve ever had a cave student that couldn’t maintain 50fpm.

But, who the phuck cares? Quit being pedantic. I was cave diving when EVERYONE but the wealthy was doing Intro to Cave on a single 104. Lp50s are better than that due to true redundancy.
And D. Let me know when you have 10% of my background and experience and we’ll start caring about your perspective.

Poor guy. I wish you the best of luck and I’m sorry for your loss or whatever made this…demeanor come to life.

 

[Superlyte27]

Poor guy. I wish you the best of luck and I’m sorry for your loss or whatever made this…demeanor come to life.

There’s no demeanor that came to life, I just don’t let non-sense go unanswered. We dove single 104s for DECADES just fine, but suddenly 50s aren’t safe.

Quit talking out your arse and I’ll be on your side, until then, I’m going to support knowledge and experience.