Ill have to review that when im not drunk= it 920 pm dammit. I thought the propane was most likely to offgas but I see what youre saying. In general im avoiding all that stuff and using ntane. Is there a difference on which gets more caught in the material= i probably should ignre that but at some point i thought cls meant CLOSED. now I off gas alot. I ran my forst hot loop last week and that worked well
1 Like
I highly doubt you have air in your tank because you chill your tank and pull vac to remove nitrogen . Unless you have a massive leak in your solvent tank or somewhere in your system . It’s still worth a shot to eliminate a possibility
1 Like
What is in the portion poured off each time?
So what is in the recovery tank?
1 Like
Not a VPD chart 
This would explain the loss of propane
3 Likes
The gauges being “off” screams leaks to me. I bet op has leaks.
3 Likes
Sometimes leaks occur only at low temps
3 Likes
@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
1 Like
The only issue here is overthinking things gravely.
oops i got that wrong, vapor pressure chart.
1 Like
Yep. We found that topping up with 70:30 fairly quickly lead to 60:40 in our tank…
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
1 Like
Nope.
I reckon you had it wrong because you follow @Graywolf’s cotton candy tek, and are not pouring off significant amounts of butane at the end of every run…
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 doesn’t 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.
1 Like
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 you’re 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.
1 Like
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 don’t have compressed atmosphere and you aren’t over filling the tank, so I suspect either temperature or propane enrichment is responsible for the pressure rises.
2 Likes
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 ya’ll 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:
3 Likes