What is in the portion poured off each time?
So what is in the recovery tank?
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Not a VPD chart 
This would explain the loss of propane
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The gauges being âoffâ screams leaks to me. I bet op has leaks.
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Sometimes leaks occur only at low temps
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@Chewwie Your getting blended gas but the issue with your pressure it seems to me is when you run mixes your losing way more butane then propane (due to their boiling points) so as you do your runs the mix ends up being more propane dominant. You need to keep track of your loss and add regular n butane to sustain your desired mix. Hope this helps
Alex
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The only issue here is overthinking things gravely.
oops i got that wrong, vapor pressure chart.
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Yep. We found that topping up with 70:30 fairly quickly lead to 60:40 in our tankâŚ
See: What's in YOUR solvent tank (today)?
& we went there because @TRIPPIE is correct.
I had it wrong and presumed the propane had more pressure and offgassed
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Nope.
I reckon you had it wrong because you follow @Graywolfâs cotton candy tek, and are not pouring off significant amounts of butane at the end of every runâŚ
i dont run tons of oil. Im on my 2nd pure butane tank. I used to use mixes and refill from cases of whip it too. I got a bunch of old tanks I shold list on craigslist
For starters, you have too much LPG in your 50# tank! Enough extra that immediate action is suggested.
A 50# tank holds 50# of water full and you are only allowed a 80% fill to allow for expansion.
70% n-Butane/30% n-Propane has a specific gravity of .548, so 50# water X 0.548 SG = 27.4 lbs
27.4# X .80 fill = **21.9 lbs.
I note that a 100# tank holds 44#. What are the dimension of your tank?
The second issue is fractional distillation. While liquid 70/30 mix stays mixed as a liquid, it doesnât as a gas because it has the lowest boiling point and during recovery, it comes off first.
If you are leaving LPG behind in the material after recovery, vent the tanks, have leaks in your system, or et al, your mix will change.
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Ummmm, by the time the recovery reaches the blurpy stage where I switch to high vacuum for Cotton Candy, it is more butane than propane, so the recovery is ostensibly skewed there too.
Is your recovery system active or passive?
If you have 40# in a 100# tank and still have pressure issues with fresh material on an pumped system, then I would check temperature first, and if that is within expectations I would chill the tank and bleed it for entrapped non condensable gases (atmosphere).
I would then start looking for my air leak.
Agreed. AND if youâre pouring jars for diamonds vs making cotton candy where the AMOUNT of butane lost on each run is soooo much less, an inattentive operator may not actually recognize the phenomenon.
Or may be balancing those losses with leaks on the high pressure portion of their runs.
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Not a 50# tank.
12X 12 X .7854 X 33 =3732 cubic inches
3732 X .0361 X .601 X .80 = 65#
If you are running passively, you donât have compressed atmosphere and you arenât over filling the tank, so I suspect either temperature or propane enrichment is responsible for the pressure rises.
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PS: How you measure tank height makes a difference. Is the 33" bottom extreme to top extreme, or the length of the tank wrapper.
If you are including the hemispherical dished heads, you have to compensate for the reduced volume of the hemispherical portion of the tank. Typically for our purposes, the volume to the tank is calculated on the wrapper portion.
For yaâll purists, ASME dished heads typically have a radius of one diameter, so the formula for the volume is Pi X H2 X (3r-h) divided by 3 and there is a calculator at:
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