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Filling a 100lb. propane bottle/tank

KST1-Derek Fultz

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I use propane at my home, so I've had a fill line installed to fill smaller tanks from my larger 1000 gal. tank.

When filling the smaller 20 gal. grill tanks, I simply hook up the fill line, open the valves on the tanks (big and little) and open the fill line valve. Once flowing, I use a small screw driver to open the set screw vent on the small tanks valve. This vents off gas while the tank is filled with liquid. Works well, even while it seems wasteful and is rather odiferous.

Recently, I picked up an older 100 Gal. propane tank to use on my gas forge because the little grill tanks where freezing up. I converted an old 2 wheeled dolly I picked up off Craigslist to transport the 100 gal. tank between my home tank and the shop and got them both painted up nice. While preparing to fill the new tank, I noticed that there is no vent on the valve. I looked at new 100 gal. tanks at Menards, same fittings etc. (no OPD), but they have a thumbscrew type vent.

Is this an issue? Do I just fill the tank without venting? Is there another way? Do any of you have experience with this?

BTW, the cap shown in the pic is from an O/A cylinder. It's just sitting there to keep the snow and ice (coming soon) off of the valve.

I'm going to go by my dealer when I get some time to get some answers. Any help in advance would be greatly appreciated.




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The empty, tare and full weight are stamped on the tank. They will vary from tank to tank. I have talked to my propane supplier about filling smaller tanks and they would not allow it. From this I "assume" that you are using an unauthorized connection. So be very carefully and be aware that in the event of a "mishap" you will be responsible for any damage to the tank and neighborhood. If you have had the proper training and tools, go for it. This is not something I would recommend for the inexperienced to do. All it takes is for a spark and the wrong mixture in the air and we would be reading about it in the papers.:o Personally, I take my tanks, both 20 and 100 pounders down to the propane supplier and let them take the liability for filling them. I am a boiler inspector and have listened to way too many horror story's in my travels so I tend to be a bit cautious about explosive gas mixtures. In any case keep the wind at your back and don't smoke. :)

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Hi Derek,

I'm a full time fire guy and HazMat operator, degree in fire protection and safety technology. I am not a preachy kind of guy and so I am not going to preach...

but you've definitely got to measure your quantity somehow, either by weighing it or by some other method, and not fill over 80% capacity. You can be sure and certain that filling over 80% is way, way more dangerous than any salty old timers would have you believe. I cannot tell you how much this is stressed in chemistry of hazardous materials courses. I won't drone on about why it's so dangerous, but believe me when I tell you, it is plenty dangerous, no matter how lucky we all may have been over the years.

And don't forget the most important little gem of information when working with propane: that the vapor is heavier than air, and isn't venting off harmlessly, but rather is hugging the ground seeking an ignition point and an explosive mixture. Our fun loving friend Propane would just love to make orphans out of all our kids.

Ok I said I wouldn't preach.

Edited by MarkC
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Thanks for the info guys. This is an "authorized connection" installed by my propane supplier, who also owns the tank. I've been trained by the supplier on how to fill the smaller tanks, it's just that this older one is different. I intend to contact my supplier before attempting a fill. Just looking for additional points of reference.

I work as a safety guy so I know all about risk assessment and training. I also know that with the proper equipment (which I have), and the proper training, which I'll get, I should be able to do it just as safely as the next guy.

Thanks for looking out for my safety.


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As I said, with proper training and tools. Go for it.
Local rules must be different in your area. They laughed at me when I asked them about filling my bottles on site. With out a vent, you will properly need a pump to fill the 100# tank. It will only fill partially, until the pressures equalize in the tanks. As I am sure they will tell you, fill it on a scale to get the proper fill percentage by weight. The Correct weights are stamped near the top for each tank.

Next week, we will talk about acetylene, balloons and burning strings.........see the pretty flash...wheres the ointment?

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  • 8 years later...

Derek as you probably already figured out you didn' need to worry about overy filling without the vent you only get equal pressure propane which isn't much if you have an old bbq grill cylider you can take the fitting out if it and screwup on your 100 lbs. And I'd but I've been filling propand botttles like this forever and I go until I'm getting liquid out the vent which I'm guessing is about 100% full only problem I have with that is once in awhile when I start new bottle it will freeze up my low press. reg. 


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