# Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?



## jbeall (Dec 3, 2009)

Hi All,

We've got 1000 gallon in-ground propane tank here at our house, and I would sure love to be able to fill small propane cylinders off that tank. We pay $2.39/gallon, with taxes and delivery, for the propane in the tank, and to get a 20lb cylinder filled or exchange we pay quite a bit more than $2.39/gallon. Plus there's the hassle of driving out to a filling station.

In high school I worked at a garden center and filled probably hundreds propane tanks at their filling station. I got the safety training about how to fill these things, and I think I remember most of it 

I talked to my propane supplier, Thompson Gas, and they're not willing to put in the propane line that I would need to hook it up to a 20lb cylinder. Worried about liability and all that.

Maybe I could get the lines and fittings to do this myself... Anybody here done what I'm considering? Propane is hazardous, and it does cause me some concern to be working with gas lines. Filling a tank with lines that a professional has run already is one thing--running the lines myself is a whole new thing.

I've even been thinking about converting various engines on my property (tractor, car, motorcycle, etc.) to run on propane and filling off my own tank, but it sounds like filling off my 1000 gallon tank is going to be more of a headache than I thought. The whole reason was to save money--I can get propane at about 35% cheaper than I can get gas. Even with the lower energy content of propane than gasoline, I'm still saving money with the price difference being that big. Plus, I don't have gas cans I have to run out and fill up for all my equipment!

-Josh


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## Ron6519 (Mar 28, 2007)

To quote John Lee Hooker, "Boom, boom, boom ,boom"


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## Mr Chips (Mar 23, 2008)

Is this for your bbq grill? If so why not ask your propane supplier to if they will do a direct line for you. Where I used to live a couple of my neighbors had this done. If i remember correctly the propane provider was happy to do it, and the only requirement was that they required you to remove the wheels from the grill and bolt it to the deck, so the grill wouldn't blow over in a storm and rip the line open.


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## Thurman (Feb 9, 2009)

First: Can you "fill" a small propane cylinder from a 1000 gallon tank?
Yes you can. 
Can this be done safely? Yes it can, with proper training and equipment.
Would it be wise for a DIY/homeowner to attempt to do this? NO and NO.
If you have the equipment to attach a smaller propane tank to your 1000 gallon tank, you could only put as much propane in the smaller tank as it would take to _equalize_ the pressures within both tanks. This will not necessarily _fill_ your smaller tank to it's rated capacity.
If you've ever noticed at the propane filling stations they use a pump to put the propane into any cylinder. This is so they can put the rated _volume_ of gas within the cylinder. 
YOU cannot put any more volume into your smaller tank than would be proportional to the pressure, NOT volume, within the larger tank.


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## Ron6519 (Mar 28, 2007)

I thought you filled propane tanks like you filled a water bucket. The larger tank filled the smaller tank under it as the liquid propane flowed down.
If your main tank is under the fill tank, wouldn't you need a pump(under the liquid/gas interface) to get the liquid up into the fill tank? 
If you just added a line, you would only get propane gas. And that would be of little use because the amount would be very small in the fill tank.


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## jbeall (Dec 3, 2009)

Ron,

What Thurman outlined, that the pressure would equalize, is what I thought would happen. I thought the pressure in the larger tank would overcome the effects of gravity and give me a partial fill in the smaller, 20lb cylinder. E.g., if my 1000 gallon tank was 60% filled, my 20lb cylinder would wind up 60% filled.

I can get regular deliveries and make sure that my 1000 gallon tank stays mostly-full, in which case I could be filling my cylinders to mostly-full.

One thing I'm wondering on the filling is, wouldn't it be just the same as the tanks I filled in highschool, only since it's not a pumping station I would only get the partial fill? In fact it seems like it would be safer. When I worked at the filling station, we had a scale to weigh the tanks and make sure we weren't overfilling them based on their rated water capacity and tare weight. But if I'm not using a pump, just letting the pressure equalize, then it seems like it wouldn't even be possible to overfill the tank... ???

So I'm unclear on how it would be more dangerous for me to fill these tanks off my 1000 gallon tank than it was filling them at the filling station.

-Josh


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## jbeall (Dec 3, 2009)

Initially this would just be for a grill, but I'm interested in being able to fill cylinders that are used not just at my grill, but at other grills, or for things besides a grill (e.g., propane space heaters). And I'm also interested in propane engine conversions (e.g., see this video: http://www.youtube.com/watch?v=SHA6C5-HG60 )


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## gregzoll (Dec 25, 2006)

$18-25 is too much for a propane exchange on a 20#. Keep two of the tanks, which most do, so they do not have to run into town during the middle of a bar-b-que.


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## Ron6519 (Mar 28, 2007)

jbeall said:


> Ron,
> 
> What Thurman outlined, that the pressure would equalize, is what I thought would happen. I thought the pressure in the larger tank would overcome the effects of gravity and give me a partial fill in the smaller, 20lb cylinder. E.g., if my 1000 gallon tank was 60% filled, my 20lb cylinder would wind up 60% filled.
> 
> ...


Are you filling the tank with a gas or a liquid?
"So I'm unclear on how it would be more dangerous for me to fill these tanks off my 1000 gallon tank than it was filling them at the filling station."
Are you using the exact same pumping system as a commercial filling station?


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## Bud Cline (Mar 12, 2006)

> Are you filling the tank with a gas or a liquid?


That's the key I think. To tap into the topside of a propane (L.P.) tank and bleed off into a smaller tank would only be moving vapor and only until the pressure variance between the two tanks equalized.

You need the liquid, not the vapor.

What you buy when your supplier fills your large tank is Liquid Petroleum. The product that you burn is the off-gas.

The liquid would need to be pumped into the smaller container for you to get anything more than an odor.


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## Jackofall1 (Dec 5, 2010)

I have attached an article that I have found, hope this clears things up, but as in the last paragraph, "You should never fill a small tank from a big tank", you could potentially overfill the small tank removing any space needed for temperature change, and create a boom, boom.

http://www.gswagner.com/propane/propane.html

Mark​


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## Bud Cline (Mar 12, 2006)

And that link right there is one that represents what is wrong with the Internet.:yes:


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## jbeall (Dec 3, 2009)

Yes, it was a "commercial filling station." We ensured that we weren't over filling the tanks by looking at the tare weight, the rated water capacity, and using that to determine the weight of the tanks when they were at 80% full. The tanks were then placed on a scale while we filled them. Is that still how it's done at a filling station?

Regarding liquid vs vapor, I had been thinking that the increase in pressure in the small tank would cause the vapor that moves to the small tank to condense. After all, it's only because the gas is under pressure that it's liquid in the first place--unless it's 45 below zero, propane is going to be a gas. So you put it in a tank under pressure, and the pressure increases the boiling temperature.

So, I had been thinking that when you bleed a big tank into a small tank, you'll first move vapor into the small tank. As the vapor is moving into the small tank, the pressure will increase in the small tank until the pressure is equal to that in the big tank--once the pressure in the small tank and the big tank are equalized, some of the vapor in the small tank will condense into liquid form because the increase in pressure has moved the boiling point above the ambient temperature of the tank. The condensation in the small tank will reduce the pressure in the small tank, which will cause more vapor from the big tank to move to the small tank (pressure continues to try and equalize), until the small tank and big tank have an equal percentage of propane (e.g., big tank 60% full, small tank 60% full).

That's all assuming the tanks are at the same temperature, but I'm thinking they won't be terribly different in temperature in real life even though I know they won't be the exact same.

So... can someone explain where I've gone wrong in my analysis of vapor vs liquid in the small tank?


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## Tom Struble (Dec 29, 2008)

do your neighbors know your attempting this?


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## Jackofall1 (Dec 5, 2010)

Your topic caught my interest and did some research, I believe that Ron hit the idea on the head, in order to fill your 20# tank you would need a wet valve on your big tank (at the bottom of the tank) and would have to either release pressure in the small tank or set the small tank in ice.

Mark


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## Jackofall1 (Dec 5, 2010)

Here is another link which is far more informative.

http://yarchive.net/car/rv/propane_refill.html

Mark


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## Bud Cline (Mar 12, 2006)

Isn't the Internet a wonderful research tool?

One minute we know nothing and the next minute we are experts.


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## Jackofall1 (Dec 5, 2010)

Thats funny, expert, hardly, would I do it absolutely not, have many other done it successfully, yes absolutely.

You sound skepticle, but I believe that is your nature.

Mark


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## Ron6519 (Mar 28, 2007)

Tom Struble said:


> do your neighbors know your attempting this?











Where's jbeale?
Over there, and there and...
Boom, boom, boom, boom.


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## Bud Cline (Mar 12, 2006)

I exhausted everything I knew about it in my first post. The only reason I knew that about it is because we use propane and when I allowed the tank to run out accidentally I got my butt chewed on by my propane supplier and then they had yo come out a perform some kind of a phony "TEST" before they would fill my tank. Running out of propane is a no-no.

They charged me forty dollars for the test so made sure I was there to observe the "testing" process. What a crock of crap that was. In the meantime I learned about liquid propane and gaseous propane. They charged my tank with vapor only to do the test. Vapor equalization in my tank necessary to perform the test resulted in the condensing of about 1/5 of a gallon of liquid I was told.

Personally I think what is being suggested is a bad idea. Skeptical is hardly the word to use.

Some things of a dangerous nature are just better off left to those that have the experience. I have an old tree stump I would love to blow to smithereens but you won't see me concocting an explosive and setting-off the charge.


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## Jackofall1 (Dec 5, 2010)

Perhaps a propane filling station under the tree trunk.......


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## iamrfixit (Jan 30, 2011)

We fill propane tanks for multiple forklifts this way 3-4 times a day; easily over a thousand times a year. We have a hose connected to the liquid valve on a 1000 gallon tank. It actually comes off the top of the tank, but the valve has a dip tube that reaches near the bottom to draw liquid. Most tanks have a liquid valve in addition to the vapor valve. To fill a tank you connect the hose to the portable tank, open the bleed valve on the small propane tank and as the vapor is expelled the liquid flows from the higher pressure to the lower pressure.

Our forklift tanks have separate bleed screws to vent the vapor while filling, most regular 20# tanks have a bleed screw on the side of the valve, it takes a screwdriver to open this valve, I have filled many of these. It bleeds vapor but also acts as a spitter valve. When the tank reaches the point filling should cease, liquid begins to expel from the valve. 

Propane has a very low boiling point (-44F), it rapidly changes from liquid to gas so while the liquid expelling from the vapor bleed looks different than vapor, very little is actually liquid as it changes to vapor almost immediately.

It seems as though it would be very dangerous and probably would be if you filled tanks indoors. Outside; the vapors are quickly carried away and do not build up. We have filled thousands of tanks over 30 years without a single problem.


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## fireguy (May 3, 2007)

The tank that wagner shows upended, would not be filled by a properly trained person. The rust would on the bottom of the tank would render the tank unusable. The upside down tank would put LP into the other tank, but where is the pop-off valve to release an over pressure situation? I had the recharge setup at one time so I could refill my disposable tanks. At that time, it was not illegal to fill disposable tanks, but it was against Fed DOT to transport them. My experience was the amount of propane I could put into the small tank was just not worth the hassle. Do it the safe way, not the jackleg way.

Gas, leaks make your house sneeze and go BOOM!!!


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## iamrfixit (Jan 30, 2011)

jbeall said:


> I thought the pressure in the larger tank would overcome the effects of gravity and give me a partial fill in the smaller, 20lb cylinder. E.g., if my 1000 gallon tank was 60% filled, my 20lb cylinder would wind up 60% filled.
> -Josh


It does not work this way, letting the pressure equalize you would get at most only a few pounds of liquid into the 20# cylinder no matter how long you wait and no matter how full or how large your supply tank is. To get even this much the tank would have to be completely bled down to zero pressure and cooled prior to filling. As soon as the pressure in both tanks equalize the flow completely stops. 

To get liquid to continue to flow; the pressure must be reduced in the tank you are filling, this is why the bleed screw is used. The vapor escapes the tank allowing flow from higher pressure to lower pressure. With the pressure reduction the liquid in the tank becomes very cold, even frosting the tank. This cold further slows the boil off rate minimizing vapor production.

Filling tanks with a pump is different, the more rapid flow of liquid cools the tank; this lower temp and the pressure inside the tank controls the boil off rate allowing propane liquid to be pumped in with only a small increase in pressure. The pump can easily overcome the pressure and continue filling. The tank is weighed because that is the only indication of fill level. The tank must not be filled more than 80% as this allows for expansion of the liquid. 

If the tank is overfilled; when the liquid expands it has nowhere to go and must push out the relief valve. If this occurs in an enclosed area, for instance while the tank is sitting in your trunk or stored in your garage the result could be catastrophic.


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## myowneq (Dec 26, 2011)

I do a lot of traveling with my camper. I use several devices (lights, grill, etc) that use the 1lb tanks. The camper carries 2 40lb tanks and I have 2 20lb tanks at home. I got tired of spending the money to buy the 1lb tanks and bought the adapter. I've tried to equalize pressure, but I've never got a decent fill like that and end up redoing it again quickly. Keep in mind, not sure if this is actually illegal, but it's definitely in the not recommended category. 

My procedures (learned from many others who've done this before me) are to put the small tanks in the freezer for an hour or two. *Side note* I have serialized all my canisters and have the max fill weights in grams wrote on them. They are weighed first, then frozen. Let them get really really cold. The adapter I bought is put in the tank (valve is closed). I grab one bottle from the freezer at a time and screw it into the adapter. I open the valve, turn the whole assembly upside down and let it flow for a few moments. I check the weights frequently until I get within 10% of the max fill weight. 

I think the trick here, is to turn the whole thing upside down so you're moving the liquid, not the vapor. I have no clue how you'd do that with an underground tank.


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## CaptainD51 (Nov 5, 2011)

iamrfixit said:


> We fill propane tanks for multiple forklifts this way 3-4 times a day; easily over a thousand times a year. We have a hose connected to the liquid valve on a 1000 gallon tank. It actually comes off the top of the tank, but the valve has a dip tube that reaches near the bottom to draw liquid. Most tanks have a liquid valve in addition to the vapor valve. To fill a tank you connect the hose to the portable tank, open the bleed valve on the small propane tank and as the vapor is expelled the liquid flows from the higher pressure to the lower pressure.
> 
> Our forklift tanks have separate bleed screws to vent the vapor while filling, most regular 20# tanks have a bleed screw on the side of the valve, it takes a screwdriver to open this valve, I have filled many of these. It bleeds vapor but also acts as a spitter valve. When the tank reaches the point filling should cease, liquid begins to expel from the valve.
> 
> ...


The only other thing I would add is to read up on grounding and bonding of tanks so you do not get a static discharge when dis-connecting.


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## Gary in WA (Mar 11, 2009)

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Gary


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