Transfilling using first stages?

[aquaregia]

I didn't see anything on a Google search, so I figure this must be a Bad Idea™, but I'm not sure why. Could I use a pair of first stages, an HP hose and a M-M adapter to transfill air from say an AL80 into an LP72?

 

[redacted]

You can: http://www.scubaboard.com/forums/tanks-valves-bands/323629-transferring-air-1-tank-another.html

 

[aquaregia]

Ah, I see. Another post http://www.scubaboard.com/forums/do-yourself-diy/354001-tank-equalizer-2-50-a.html

And for completeness again, a poster in another thread reported transferring about 35cf in 15min through the restrictors in the 1st stage.

 

[hypertech]

Although you can, I don't understand why you would do this. You can't fill the LP72 all the way up and then you'll be left with two half full tanks. I didn't do the math, but at most I think you could transfer something like 20 cf from the AL80 to the 72 before you reach the operating pressure of the 72.

 

[aquaregia]

It's sort of difficult to explain why I want to do this, but if my math's right I should be able to take a 500psi LP72 to 2200psi with two AL80s.

 

[fdog]

Never mind the nerdly math stuff, how did you do the TM symbol?


...BTW, if doubles are involved, make sure the isolator is closed, and you transfill each side separately...then open the isolator to balance. Good for an extra ~5% or so. Counter-intuitive but true.

Getting back to your question, you could do it the way you describe, since the HP ports are upstream of the moving bits in the 1st stage; however, bring a good book. The flow restrictors in the 1st stage will make the transfer glacially slow. Do NOT ask me how I know this.

Better off with a real live transfill whip, something every diver needs in their bag.


All the best, James

 

[hypertech]

Trade the AL80's for LP72's?

Maybe you have your own compressor, but I'd get dinged for two fills doing that and it completely wouldn't be worth it.

Let me try the math.

Starting
72@500 psi = 16.4 cf
80@3000 psi = 80 cf

First equalization
96.4 cf = x/2200 * 72 + x/3000 * 80 = x(72/2200 + 80/3000), x= 1623 psi
72@1623 psi = 53.1 cf
80@1623 psi = 43.3 cf

Second equalization
133.1 cf = x/2200 * 72 + x/3000 * 80 = x(72/2200 + 80/3000), x= 2240 psi

So, it looks like you would fill the 72, but you would end up with one half full 80 and one two thirds filled 80.

 

[mrfixitchapman]

Never mind the nerdly math stuff, how did you do the TM symbol?





All the best, James

Use the HTML character entity ™ (preferred) or the character decimal code &#8482 or the character hex code &#2122

DC

 

[fdog]

Holy cow, I just read the thread awap referred to.

...awap, I wish I knew your name, so I could thank you properly. This post of yours made me laugh so hard I quite literally fell out of my chair! Possibly the best post I've read on SB in years.

Would you care to explain what you think could go wrong??? Like , exactly where do you think the camera should be aimed? Just so we can objectively look at the real risks rather than unnecessarily bring the kids into this.

I suspect that the only real risk is a leak. No BAM, no BOOM.

Ah, the delicious irony! The subliminal dis! Not to mention just plain funny.

Thanks!


All the best, James

 

[aquaregia]

So, it looks like you would fill the 72, but you would end up with one half full 80 and one two thirds filled 80.

Add one more step and it's a full 72 and two 2/3 full 80s.

fdog, how slow? It looked like ~80cf/hr in a different post.