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Old 08-26-2011, 07:39 PM   #1
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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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Old 08-26-2011, 07:49 PM   #2
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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

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Old 08-26-2011, 09:22 PM   #3
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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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Old 08-27-2011, 08:47 AM   #4
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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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Old 08-27-2011, 10:15 AM   #5
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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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Old 08-27-2011, 11:36 AM   #6
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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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Old 08-27-2011, 11:38 AM   #7
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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: )
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Old 08-27-2011, 12:14 PM   #8
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


$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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Old 08-27-2011, 12:17 PM   #9
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


Quote:
Originally Posted by jbeall View Post
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
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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Last edited by Ron6519; 08-27-2011 at 12:21 PM.
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Old 08-27-2011, 12:35 PM   #10
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


Quote:
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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Old 08-27-2011, 12:50 PM   #11
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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

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Old 08-27-2011, 01:08 PM   #12
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


And that link right there is one that represents what is wrong with the Internet.
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Old 08-27-2011, 01:50 PM   #13
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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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Old 08-27-2011, 01:56 PM   #14
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


do your neighbors know your attempting this?
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Old 08-27-2011, 01:57 PM   #15
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Filling a 20lb propane cylinder off a 1000 gallon tank--anybody done it?


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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