tmassey
Contributor
First of all, getting a bank bottle to a cold 4500 is a challenge. You’d have to fill it to nearly 5000 psi hot, and that’s quite hard on the compressor. So your 444 cf bank bottle @ 4500 psi ends up becoming a 410 cf tank at 4200 psi. Keep that in mind.
I could break out the Excel spreadsheet and get exact numbers, but this estimate will be close enough.
Each 100 psi of bank bottle pressure represents just shy of 10 cf of gas. 2500 psi of AL80 is 65 cf, or just under 2.5 cf per 100 psi. That means you need 650 psi of a bank bottle to go from 500 psi to 3000 psi in an AL80. Starting with 4200 psi, you can fill 2 AL80’s before you hit 2900 psi in your first bank bottle. At that point, you will get short fills that need to be made up from the second bottle. The third fill will get you to about 2400, then you will need to take 150 psi from the second, leaving it at 4050. The fourth to 2000/3800, the fifth to 1700/3500, the sixth to 1400/3000.
And that’s it: you don’t have enough pressure to go above 3000 anymore. Your next fill will max out at 2600.
Why does my math differ from @Wookie ‘s experipence? Two big reasons. First, I’ve ignored temperature completely. In order to get 3000 psi fills, you’ll need to fill to 3300 realistically. That means you’ll hit the limit after just *4* tanks.
And second, notice how @Wookie gave us two numbers: filling 6 at once (literally hooking up 6 to a single valve and filling them at once) vs filling 8, by filling each tank sequentially? Doing each bank on each tank one at a time makes a big difference. You can better use your bank by working one tank at a time, one bank at a time.
But it takes a *LOT* longer to do it that way. If it takes you 30 seconds to hook up a tank and 3 minutes to get a batch of tanks from 500 to 3000 (which is fast) doing 6 at once will take you 6 minutes. Doing them sequentially will take you 21 minutes…. If you took 5 minutes to fill a tank (which is still pretty fast: those tanks will be hot), it’s now 8 and 33 minutes…
As you can see, you’re going to want to fill tanks simultaneously. And that does zero favors for your bank.
I have 4 bottles for EAN32: 4 banks of 1 bottle. I *try* to fill 3 sets of doubles, but that depends on exactly how big they are, how empty they start and how much gas I’m trying to cram in there. Even though they’re usually starting above 1000 psi, I usually want to end up at 3500 cold. And I usually don’t quite make it. I usually have to go back and top them up because I don’t have enough pressure to do it all in one shot. Topping up a couple of sets of doubles is easy. A couple of dozen AL80’s is not.
And now you know why short fills are a thing….
ETA: After all of that, I think I buried the lede. Keep in mind: the math may say one thing is possible. Reality may not match the math, however. Sometimes the math ignores real issues, such as hot fills that will cool to a lower pressure, which makes your usable capacity much smaller. And sometimes the math might assume an unrealistic process, like individually filling 24 tanks sequentially over hours of time instead of doing multiple tanks simultaneously — but which also makes your bank’s usable capacity much smaller.
One thing is for sure: filling 24 tanks quickly will need a *lot* of bank…
I could break out the Excel spreadsheet and get exact numbers, but this estimate will be close enough.
Each 100 psi of bank bottle pressure represents just shy of 10 cf of gas. 2500 psi of AL80 is 65 cf, or just under 2.5 cf per 100 psi. That means you need 650 psi of a bank bottle to go from 500 psi to 3000 psi in an AL80. Starting with 4200 psi, you can fill 2 AL80’s before you hit 2900 psi in your first bank bottle. At that point, you will get short fills that need to be made up from the second bottle. The third fill will get you to about 2400, then you will need to take 150 psi from the second, leaving it at 4050. The fourth to 2000/3800, the fifth to 1700/3500, the sixth to 1400/3000.
And that’s it: you don’t have enough pressure to go above 3000 anymore. Your next fill will max out at 2600.
Why does my math differ from @Wookie ‘s experipence? Two big reasons. First, I’ve ignored temperature completely. In order to get 3000 psi fills, you’ll need to fill to 3300 realistically. That means you’ll hit the limit after just *4* tanks.
And second, notice how @Wookie gave us two numbers: filling 6 at once (literally hooking up 6 to a single valve and filling them at once) vs filling 8, by filling each tank sequentially? Doing each bank on each tank one at a time makes a big difference. You can better use your bank by working one tank at a time, one bank at a time.
But it takes a *LOT* longer to do it that way. If it takes you 30 seconds to hook up a tank and 3 minutes to get a batch of tanks from 500 to 3000 (which is fast) doing 6 at once will take you 6 minutes. Doing them sequentially will take you 21 minutes…. If you took 5 minutes to fill a tank (which is still pretty fast: those tanks will be hot), it’s now 8 and 33 minutes…
As you can see, you’re going to want to fill tanks simultaneously. And that does zero favors for your bank.
I have 4 bottles for EAN32: 4 banks of 1 bottle. I *try* to fill 3 sets of doubles, but that depends on exactly how big they are, how empty they start and how much gas I’m trying to cram in there. Even though they’re usually starting above 1000 psi, I usually want to end up at 3500 cold. And I usually don’t quite make it. I usually have to go back and top them up because I don’t have enough pressure to do it all in one shot. Topping up a couple of sets of doubles is easy. A couple of dozen AL80’s is not.
And now you know why short fills are a thing….
ETA: After all of that, I think I buried the lede. Keep in mind: the math may say one thing is possible. Reality may not match the math, however. Sometimes the math ignores real issues, such as hot fills that will cool to a lower pressure, which makes your usable capacity much smaller. And sometimes the math might assume an unrealistic process, like individually filling 24 tanks sequentially over hours of time instead of doing multiple tanks simultaneously — but which also makes your bank’s usable capacity much smaller.
One thing is for sure: filling 24 tanks quickly will need a *lot* of bank…
