Filling 20 lb Propane tanks

[toiletuser]

I have a 500 gal. propane tank in my yard for heating. I am changing suppliers so the old company is going to come and get their rental tank. The company I have been doing business with are real a$$holes, so I want to make sure there is no gas left in the tank. The tank contains about 5% and the heating season is almost ended. If there is any gas left, I'd like to fill all of my 20lb cylinders and if needed, I can borrow several 100lb ones from a neighbor. I can always use these, and I want to make sure the bulk tank is empty, but dont want to just waste it. I have the pipe adaptors for both tanks and a certified for propane hose. Do I just connect from tank to tank, or should I do it after the bulk tank regulator?

Yes, I know that the 20 Lb cylinders should not weight more than 20 lbs more than the empty tank, and I have something to get a rough weight measurement on them. I'll underfill them just to be safe, and they will remain outdoors after I do it. Of course all this will be done outdoors too.

Has anyone ever done this? I've filled the refillable torch bottles from 20lb cylinders in the past, so I dont see this all that much different other than the amounts.

[Steve B]

All you need is one of those expensive pumps and big balls. Otherwise, all you can get in is as much as will go in until equal pressure is reached. (definition: not that much)

Steve

[Richard J Kinch]

Sure, just turn the 500 gallon tank upside down first, so you get liquid out, like you did refilling disposables from an upside-down 20 lb'er.

Expect cryogenic, flammable liquid to spew in your face, blinding you, and instantly frostbiting your skin, just before the massive explosion and fire that ends your life in a blood-curdling cry of gurgled horror, with your family and neighbors watching your staggering death-walk across the lawn as your burned lungs starve you of oxygen and you collapse.

Other than that, yep, it's just not "all that much different other than the amounts".

[Paul M. Eldridge]

Ok, I don't know about the rest of you, but I just lost total bladder control. :>)

Cheers, Paul

[Tony Hwang]

Hi, Just don't even try. Bottles are filled as liquid with special machine(pump) by the weight. Also it is safety issue. Also Propane has summer/winter grade like gasoline.

[Big Al]

Put the 20 pound tank in a tub of ice water. The gas will go in and liquefy. Weigh it or shake it to be sure it's not too full. Be sure you insurance is paid up, will is in order and so on:)

Al

[Richard J Kinch]

A propane still, eh?

Stills are expensive to run, especially on a small scale. The cost and time to process 25 gallons this way will exceed any value of the product.

Better to just vent the stuff if he insists on spiting the dealer.

[Steve B]

If you're really anal and just want to get even no matter what the cost, be sure to open the valve and let whatever's in there run out. You won't get anything, but they won't either.

Steve

[mm]

Steve B said what I would say.

Also, I have a vague feeling they buy back what you haven't used, but if so, I still don't know the details. Look at your contract.

[Steve Barker]

?????

[DAC]

Call the new company, and have them pump the tank out, and when they place the new one, have them credit you back the same amount. If you can work it right, they could pump the gas out, remove the old tank, place the new one, and fill the tank in one trip.

Have you contacted the other company to see if they would credit you the amount in the tank?

As for moving the gas with 20# tanks...while it sounds good...practically it isn't worth the effort.

Good luck.

[JoeSpareBedroom]

Can we have your address, please? I want to videotape this (from a distance) and post it on youtube.

[---MIKE---]

The dealer should give you a credit for the unused propane. This happened to me when I switched gas companies.

---MIKE---

[Zephyr]

I'm going to say ditto to this post.

The propane needs to be under huge pressure to stay in liquid form, once you start to release that pressure from the big tank into the little one, all you will be getting is the gas, not the liquid form. so, like another mentioned, you would have to flip your big tank upside down, or drain it from the bottom. Much better to just get the new company to pump it out.

as for screwing your old company. If you do open the valve on the old tank after it has been pumped empty, the old tank will need to be purged before it can be used again, so. that would be one way of "stickin it to em"

[Karma Ghia]

I would seek out a company that will sell you a tank, the rental scam is expensive. good luck!

[Jeff Wisnia]

That sounds like it should work.

But, it reminds me of something I once wondered about and I don't remember ever if I ever got an answer fo.

Take two similarly sized and shaped propane containers, one nearly full of liquid and the other nearly empty and couple them together with a tube between their tops.

If they are left undisturbed long enough in a constant temperature environment of say 70 F, will the liquid levels in the two containers eventually equalize on their own, and if they will, what's the physics behind it?

Jeff

[Steve B]

---MIKE---

They did it for me, too, when I switched electric companies............

Steve

[Dan Espen]

Theoretically all the gas could move into just one tank due to random motion, but you might have to wait the lifetime of several universes before it happens.

Basically the random motion tends toward equal distribution and for the setup you describe I'd think a second or 2 would be enough so that you couldn't measure the difference.

IANAP

[Ook]

Yeah, I gotta question that one also. Gasoline is a complex chemical with a lot of different things going into it's makeup. Propane is a simple compound, C3H8, and only comes in two configurations, propane and cyclo propane (which you won't find in any propane tanks). AFAIK they only thing they add to it is the oderant that gives it the garlic stench (propane itself is odorless and colorless, the smell you smell isn't the propane). Summer/winter grade? I seriously doubt it.

[Jeff Wisnia]

I decided the guys on sci.physics would know about this sort of stuff and posted my question there too. I got a believable and understandable answer back which I'll snip and add below.

I now see why, given a LONG TIME, and under the influence of the earth's gravity, the liquid levels in the two tanks WOULD approach equal heights, but it would take an infinite amount of time for them to become eggsackly equal.

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Pressure of the propane vapors changes with altitude. There's only

12 inches or so of altitude to play with inside the tanks, but if all other things are equal, this will come into play and eventually the tanks will equalize with the propane at the same level even though the tanks are only connected at the top.

Propane will evaporate from the surface of the more-full tank since the vapor/liquid interface there is at a higher elevation and, hence, at a lower pressure than in the less-full tank.

One might estimate the rate of transfer by figuring out the pressure differential (what is the density of propane vapors at room temperature and what is the difference in fluid levels?) This pressure differential equates to a temperature differential (how does the vapor pressure of propane vary with temperature?) This temperature differential equates to a rate of heat flow (what is the R value of a pair of steel tanks of propane in air?) This rate of heat flow equates to a time parameter (how much heat does it take to vaporize a one cm layer of propane in a

30 cm diameter tank?)

This should lead to a first order linear differential equation whose solution is an exponential decay in the difference in fluid levels over time.

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