The Great Helium Hunt of 2021

[CptTightPants21]

I have a hopefully not so dumb question. When filling from a compressor let's say I want 32%. So I figure to fill a set of 3500 tanks to 3900 (because they'll cool and I like more gas) I need to add ~ 543psi of O2. I do this and the tanks get a little warm, I pump up to 3900, shut things down and let things cool off. Will I still have my desired 32% when things cool down. I would expect somewhere around ~ 3600 or so? And if so, why would it still be correct? My final pressure isn't 3900.

I actually did this the other day (was shooting for 28%). Even after the tanks cooled down I still ended up having what I wanted within .2 of 28%. I was unsure whether I would have to top them off after they cooled but I did not.

I'm sure there are some physics here that I'm just not grasping.

Ball Park, yes. Target goal is within .5% of target O2 and 5% within target helium goal.

Each fill station and gauge has it's own little quirks that you learn to adapt to/utilize.

For example, a cold 543 psi like in your example would actually lead to 33.2% nitrox when cooled to 3500.

So naturally, that O2 number went in a little hot and was there for slightly less than an actual 543psi. Give or take a little gauge variance, throw in some more air (say it was actually 3600 when cooled) and you basically ended up dead on for your desired mix.


Biggest factor with O2 is heat and with helium it is heat and compression. I try to do trimix blends over two days if I can.

Your math should be working in final cooled temperatures.

There are a couple different factors that come go into play and you manage/guesstimate them as well as you can. Do I need to haskel the O2-how much? How fast do I want to get this fill done? How high are my air bank bottles?

If I am working with a brand new T of O2 and I don't need to haskel, then I can set the flow at a moderate 1psi every 1 to 1.5 seconds and I know that the tank I will filling will stay cold and I just need to fill the calculated O2 number exactly.

Needing to haskel creates some more heat which can affect the final mix. So I haskel a little more O2 to compensate for the heat, knowing that worst cast scenario I can dilute it down with more air from my filled high bank of tanks.

The air top up goes 300-400 PSI over target fill pressure and will cool to desired pressure and mix.

 

[Manatee Diver]

The first one is correct, the second one is off by a small factor (it's more like 5:3) and you'll never get 30/30 by mixing only 10/70 and 32%.

That explains why I have to adjust my 18/45 fills to hit my desired mix.

 

[rob.mwpropane]

Ball Park, yes. Target goal is within .5% of target O2 and 5% within target helium goal.

Each fill station and gauge has it's own little quirks that you learn to adapt to/utilize.

For example, a cold 543 psi like in your example would actually lead to 33.2% nitrox when cooled to 3500.

So naturally, that O2 number went in a little hot and was there for slightly less than an actual 543psi. Give or take a little gauge variance, throw in some more air (say it was actually 3600 when cooled) and you basically ended up dead on for your desired mix.


Biggest factor with O2 is heat and with helium it is heat and compression. I try to do trimix blends over two days if I can.

Your math should be working in final cooled temperatures.

There are a couple different factors that come go into play and you manage/guesstimate them as well as you can. Do I need to haskel the O2-how much? How fast do I want to get this fill done? How high are my air bank bottles?

If I am working with a brand new T of O2 and I don't need to haskel, then I can set the flow at a moderate 1psi every 1 to 1.5 seconds and I know that the tank I will filling will stay cold and I just need to fill the calculated O2 number exactly.

Needing to haskel creates some more heat which can affect the final mix. So I haskel a little more O2 to compensate for the heat, knowing that worst cast scenario I can dilute it down with more air from my filled high bank of tanks.

The air top up goes 300-400 PSI over target fill pressure and will cool to desired pressure and mix.

I got a lot out of your post, thanks. At the end of the day, that's what I figured, each unit has it's own quirks.

How long do you wait to test the mix? A day? I know I'll learn my own system better as time goes on, just curious what others practices are.

Tbh, I'm just super grateful to get a mix even remotely close that I don't have to drive and pay and arm and a leg for.

 

[Marie13]

Found out that I’ll be paying $4.60/cft not $4.80 when I dropped my tanks off tonight. I had misremembered. I’ll take it!

 

[Wookie]

Found out that I’ll be paying $4.60/cft not $4.80 when I dropped my tanks off tonight. I had misremembered. I’ll take it!

Like finding money in your pocket. It was always your money, but somehow it seems like a bonus.

 

[Marie13]

Like finding money in your pocket. It was always your money, but somehow it seems like a bonus.

haha. Yep!

 

[happy-diver]

Scavenging helium

 

[Marie13]

So for some real sticker shock for you folks -

3000 psi fill is $88.32 per tank for just the He for 20/20. $353.28 just for the He for Saturday.

 

[Wookie]

So for some real sticker shock for you folks -

3000 psi fill is $88.32 per tank for just the He for 20/20. $353.28 just for the He for Saturday.

Training is expensive. What certs will you get? Normoxic and recreational?

 

[Marie13]

Training is expensive. What certs will you get? Normoxic and recreational?

TDI Advanced Nitrox/Helitrox. Up to 35% He down to 150ft. I have a lot of diving in that range to do. Deco Procedures falls under Helitrox. You don’t get the DP card (some instructors seem to give it), but do the DP bookwork.