Is there a reason that these butane tanks only come with 25 lbs. The capacity of the recovery tank is 80% of the WC weight listed correct? So if I have a 50 lb tank and the WC is 47lb, I can recover up to 37 lb?
This always confused me as well. I’m hoping someone can shed some light onto this.
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You need to account for the difference in density between water and n-butane.
Specific gravity for n-butane @25C=.601
47lb WC X .8 X .601= 22.6lb n-butane capacity @ %80 full @ 25C.
Your tank can only hold 28.2 lb n-butane total before it’s completely full at room temp.
For some perspective:
1 gallon water==== 8.3 lb
1 gallon n-butane= 4.8 lb
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Thanks thats what I was looking for
Hey. I found your answer when digging for the same info OP was looking for.
But I’m curious, is there a calculation or handy chart to find specific gravity at other temperatures aside from 25 C? Googling liquid butane specific gravity seems to only return the value of .601 @ 25 C.
Tank capacity should always be calculated at an 80% fill at 25 C as that is the standard ambient temperature. Yes you can fill more at a lower temp but that doesn’t mean that you should, especially if you’re talking about storage. To fill more you would need your tank to be stored at that lower temp indefinitely and that becomes a hazard.
BVV has a useful calculator on their site but their calculator also assumes a 80% fill at 25 C.
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I didnt want to clutter the forum and start a new topic but can anyone tell me what numbers im looking for with a 70/30 mix? Im filling up a 50lb yellowtop tank and a ~30lb tank from bhogart in series. I have a 100lb tank of 70/30 and want to fill these tanks safely but ive looked on google and searched the forums here and cant find a solid answer. Any help would be appriciated!
Here’s the answer, the mix is close enough to the weight of butane to use that.
Or just fill em to half the stated capacity, it’ll be close to 75% full.
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Thanks miner! Ive seen those numbers but i guess im asking what i should see on my scale if i have the tank on it empty vacced down. I think im overthinking it for sure im just trying to be safe filling these things from empty lol but the lb - gallon conversion is just not making sense to me 
ignore gallons, tare the tank and dont put more than 22 lbs in it.
thank you bro
I think for propane its more like 18 lbs. It has more pressure or lighter weight so the tank holds less
Any idea on why im only able to put about 5.5 lbs in each tank before my big white one doesnt have enough push to put anymore in? Do i need to use my pump to suck it into my solvent tank from big supply?
Chill the tank you’re trying to put gas into or heat up the larger LP tank you’re pulling from. The large tank is likely getting too cold from moving solvent or the smaller tank hasn’t compressed all of the gas into liquid. Either way, there is a pressure equilibrium so no solvent can move.
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Assume:
50# is Water, which weighs .0361 lbs/in3
50# divided by .0361 = 1385 in3
80% fill by volume or .80 X 1385 = 1108 in3 filled.
Specific gravity of butane is .601 or .0361 X .601 = .021696 lb/in3
Specific gravity of Isobutane is .563 or .0361 X .563 = .0203243 lb/in3
Specific gravity of propane is .495 or .0361 X .495 = .0178695 lbs/in3
Therefore:
100% n-Butane = 1108in3 X .021696 = 24 lbs. total
-----------------------------------------------------------
70:30 = (.7 X 1108 in3) = 775.6 in3 butane + (.3 X 1108 in3) = 332.4 in3 propane
(775.6 X .021696) + (332.4 X .0178695) = 16.8 lbs + 5.9 = 22.7 lbs total
-------------------------------------------------------------------
50:50 = (.50 X 1108 in3) = 554 in3 butane and 554 in3 propane
(554 X .021696 lb/in3) + ( 554 x .0178695 lb/in3) = 12 lbs butane + 9.9 lbs propane = 21.9 lbs total.
------------------------------------------------------------------------
20:20:60 = (.20 X 1108 in3) = 221.6 in3 and (.60 X 1108) = 664.8 in3
(221.6 X .0179695) = 3.98 lbs propane + (221.6 X .0203243) = 4.5 lbs Isobutane + ( 664.8 X .021696) =14.4 lbs butane or **22.88 lbs total.
100% n-propane = 1108in3 X .0178695 = 19.8 lbs**
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That was my assumption as well
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What is capacity of receiving tank?
After vacuuming the receiving tank, as FH noted, put it in an ice bath and add heat to the supply tank.
Good points!
Knowing the tare of your tanks is important. I suggest stamping it on each tank, if it isn’t already stamped.
22# max in a 50# tank is a simple solution that would keep you in the safe zone, albeit a little over for propane and under for butane.
Where the math comes in handy is mixing and analyzing.
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Ah I been looking for these calculations. Gonna make a handy dandy calculator so people can just input and have on the fly answers. Bookmarked.
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that indicates air in the tank. Get them so cold its below vapor pressure and vent off the air outside.