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Filling a Propane Tank From a Propane Tank Questions

Wayne 440

Registered
My experience has been that it takes longer as the temperature decreases, you probably just didn't wait long enough.
 

DustyBar

Subscriber
Last Subscription Date
01/14/2020
We always filled farm machinery tanks in the field by opening a vapor valve and filling through the liquid valve. Occasionally we would be filling in a farm yard. I often questioned what was happening to the propane vapor we discharged into the air. I knew it was heavier than air and could settle in low areas. I questioned the wisdom of venting a tank around buildings, especially a house with a basement nearby. No explosion ever happened where I was working but it was Kansas where it was always windy and probably dissipated the vapor.
 

Odin

Subscriber
Last Subscription Date
07/13/2019
Thinking about this a little, opening the bleeder on the tank being filled would make the pressure in that tank drop, and the liquid in that tank evaporate to maintain pressure, making the tank cold.

Being colder, it would then have a lower vapor pressure than the nurse tank, and the liquid would flow without a pump.

So yes, the method described makes sense in how it works, and really could produce a full tank.

The drawback of course being that you are venting clouds of propane gas, which has its fire risks and is itself a notable pollutant and greenhouse gas. Plus you do have to pay for that propane you are throwing away in order to power the transferring process.

I guess most fill stations just use pumps to do it because it works more efficiently, and doesn't release anywhere near as much propane to the air in the process.

The forklift bottles at work serve up liquid propane on their taps, and have recapture fittings to stop the flow when the fitting is disconnected. You get a good spurt of liquid out of it and then nothing, as the fitting has captured the flow. Perhaps you could make a filling adapter using these by connecting one to the standard OPD tank nose, that way when the liquid line is disconnected the remaining propane is captured within it. The liquid on the recieving side would boil off and make its way down into the tank, while the liquid on the supply side would remain so for some time.
 

s100

Registered
I for one would not try this for any reason under any circumstances. The potential for a major disaster is just too high. The venting propane gas (from the vent), steel things around, it's cold and you may be wearing a wool sweater, these are just two potential spark sources of many. Or some bonehead may show up on your doorstep, puffing on a cancer stick just as you are refilling. Please, please reconsider this madness. I get chills just thinking about it.

A couple of years ago someone living a half mile away had a gas bbq set up under a canopy off the back of his house (mistake number one). He lit the burner but something malfunctioned. The resulting fire nearly burned his legs off and did burn his house to the ground. Yes others here seem to have had good luck refilling these tanks but all it takes is ONE thing to go wrong ONE time and it's all over. It simply isn't worth the risk.

Nobody hates making repeated trips to the store more than me, so I understand your motivation all too well but in this instance I would gladly make a trip a day to avoid such a risky alternative. And there ought to be other options available. How about getting a few more tanks? If you use let's say two tanks a week, and you have two tanks, getting just two more halves the number of trips you need to make, a trip every other week. Or is there some way you can plumb the bigger tank to your consuming devices? Seems to me that would be the first thing I would consider. I may also be the cheapest person on the planet but I would switch to electric heat before I'd do what you are attempting.

Some people may say I am over reacting and that is fine. People do what they will do. To me though I am happy to apply an overabundance of caution to a situation where the risk/value equation is so skewed.
 

BHoward

Registered
Last Subscription Date
05/04/2018
I agree with s100 , just Google Toronto propain explotion. An employee was transferring propain from one truck to another.
 

Odin

Subscriber
Last Subscription Date
07/13/2019
A couple of years ago someone living a half mile away had a gas bbq set up under a canopy off the back of his house (mistake number one). He lit the burner but something malfunctioned. The resulting fire nearly burned his legs off and did burn his house to the ground. Yes others here seem to have had good luck refilling these tanks but all it takes is ONE thing to go wrong ONE time and it's all over. It simply isn't worth the risk.
Have previously experienced an unwelcome fireball beneath the bbq before. Before the rise of OPD tanks, when we still used POL nose fittings without excess flow valves or any of that safety gear, I once had the fuel hose between the regulator and manifold develop a leak while grilling. Made a very inconveniently located fireball about knee height, that persisted until I shut off the tank while wearing gloves that I had nearby for dealing with hot plates.

A total rupture of the fuel hose in that situation would have produced a fireball sufficient to ignite the siding of a house, and kill whoever was nearby when it was let loose. Modern OPD tanks actually have excess flow valves in them to shut off the fuel automatically in this scenario and minimize the extent of the damage.
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
What are you using the 20 pounders for? if you have the big tank on site, it might be better if you ran hard piping to your use points, and use the big tank for your supply. As others have noted, you can only fill until tank pressure has equalized. The best you can get is 1/2 a tank, unless you can chill the receiving tank to lower the internal pressure. Unless you have a transfer pump for the propane, you probably will not be able to fully refill the small tanks to capacity. besides that, you are losing a lot of gas just venting to the atmosphere, especially if the tanks have some residual liquid in them before your refill efforts. trying to refill tanks with open venting is a disiaster waiting to happen. I would not do it. it's just not worth the hazard to do it in that manor.
 

Heins

Subscriber
Last Subscription Date
01/02/2020
s100, what do you think farmers should do to fill their tractors back in the 50's when they are 20 miles from town and it is 100 degrees out if they couldn't vent the tractor to fill it. The problem with city people is they have propane inside. Farmers should fill the tractors 80 or 85% but if they are going to farm, they will fill them 100% and get to farming. When my propane guy comes to fill our 500 gallon tank, I will have him fill our smaller bottles.
 

dalmatiangirl61

Subscriber
Last Subscription Date
07/10/2019
Oy vey! Ask for a little advice on propane and now you guys are talking about explosions, lol. I have a 2 acre fenced yard and no real neighbors, I guess if transformer blows while filling tank I might have a problem. 20lb bottles are currently being used to run the UNVENTED heater in my room, I have a CO alarm and a CO meter, I have not died yet. There is a plan to run propane into building and install a vented propane heater, maybe next year. Its a project home, I cannot get more done here until I can stay here year round, so things get done in stages, its the best I can do.
 

s100

Registered
"s100, what do you think farmers should do to fill their tractors back in the 50's when they are 20 miles from town and it is 100 degrees out if they couldn't vent the tractor to fill it. The problem with city people is they have propane inside. Farmers should fill the tractors 80 or 85% but if they are going to farm, they will fill them 100% and get to farming. When my propane guy comes to fill our 500 gallon tank, I will have him fill our smaller bottles."

I was expecting this one.

The situation of a farmer out in an open field a long distance from anyone and anything is a lot different from a person in close proximity to a house and also in closer proximity to more spark sources. Also there's not much more he can do if the stupid tractor runs out of gas. I think the only reasonable thing he can do is to become double jointed and kick his own backside for buying a white elephant tractor that does not use diesel fuel.

"Oy vey! Ask for a little advice on propane and now you guys are talking about explosions, lol."

Yes we are talking about one with the idea in mind to avoid one. I have nothing to sell here and no interest beyond keeping our little community safe. Do what you must, I guess, to keep yourself happy.

p.s. Farmers are some of the greatest risk takers in our society, in any of a myriad of ways. Farmers provide us with what we arguably need more than anything, our meals. I have the greatest respect for our farmers and want to see them safe and happy.
 

Vanman

Subscriber
Last Subscription Date
07/10/2019
I always thoight that the proper proceedure for filling propane cylinders was to open the bleed valve so you know when they are full. As far as I remember all service stations used to do this. Their filling location is always out in the open and well away from anything else.

Since the OPDs, they don't do this. That's how I learned that one of mine does not work. That tank was BRIM full, and my regulator sucked liquid for quite a while. Now I always make sure they stop at 4.7 gallons for a correct fill.
 

Heins

Subscriber
Last Subscription Date
01/02/2020
When you have a large tank and pipe the propane into the house and use a pipe underground, the pipe has to come above ground before it goes into the house. That way if you have a leak in the underground pipe, the propane won't follow the pipe into the house. They won't fill your propane tank if the pipe doesn't come above the ground before in goes into the house.

I helped a guy brand calves back in the 60's and we used a propane weed burner to heat the irons and the propane bottle was a 100# bottle. After we branded about 1/2 a day the propane bottle frosted up and the propane wasn't boiling fast enough (it was summer time) so the owner took the weed burner and turned it on the bottle to warm it up every one started to run. It warmed the bottle up and we went back to branding.

s100, don't call the propane tractors "white elephants", back in the 50's propane was $.07 and diesel was $.15 per gallon. It was a toss up which was cheaper to run. Propane tractors used two gallons to one gallon the diesel tractors used.
 

oldtractors

Registered
Age
50
Last Subscription Date
12/22/2015
Has anyone ever filled a lawnmower with a gas can? That is more dangerous than filling a LP tank. Also, the amount of gas you are venting while filling a 20 lb tank is probably 1 -2 ounces. Less than what you spilled on the ground while filling your lawnmower.
 

OTTO-Sawyer

Subscriber
Age
58
Last Subscription Date
07/15/2019
The situation of a farmer out in an open field a long distance from anyone and anything is a lot different from a person in close proximity to a house and also in closer proximity to more spark sources. Also there's not much more he can do if the stupid tractor runs out of gas. I think the only reasonable thing he can do is to become double jointed and kick his own backside for buying a white elephant tractor that does not use diesel fuel.

p.s. Farmers are some of the greatest risk takers in our society, in any of a myriad of ways. Farmers provide us with what we arguably need more than anything, our meals. I have the greatest respect for our farmers and want to see them safe and happy.
So you apparently think tractors ONLY GET REFUELED Out In The Field and Never by the House or Barn or Machine Shed ? :rolleyes:

You say you Respect Farmers but proclaim they should kick themselves in the ass for buying a propane powered tractor ? :bonk:

Also as an added side note: They Refuel Diesel Tractors out in the field too if they're getting low rather than driving them all the way back to the farm/buildings so calling out the Propane users for doing that was kind of pointless. Kind of like hitching up the horses to haul more Coal & Water out to the Steam Engines while they're plowing. ;) No White Elephants Involved, just doing what they needed to do in order to stay out in the field longer.

:salute:
 
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DustyBar

Subscriber
Last Subscription Date
01/14/2020
s100, what do you think farmers should do to fill their tractors back in the 50's when they are 20 miles from town and it is 100 degrees out if they couldn't vent the tractor to fill it. The problem with city people is they have propane inside. Farmers should fill the tractors 80 or 85% but if they are going to farm, they will fill them 100% and get to farming. When my propane guy comes to fill our 500 gallon tank, I will have him fill our smaller bottles.
Yep, thats exactly how it was done even as late as 1990's on our farm and I'm sure still is elsewhere. I think the tractor tank was around 80 gallon capacity and that is the only way we ever filled it. Now we had a helium plant nearby and propane was an unwanted byproduct. I remember it as cheap as 16 cents a gallon all through the 1960's. Not only that my dad once got a rebate check for having been overcharged for propane several years. Loss of a gallon or two of propane while filling was no big deal while maintaining pumping equipment would have been. I'm sure that would have been electric powered, sometimes miles from an electric service. Since I did most of the plowing I would fill them to nearly 100% if I immediately started again after filling otherwise to 80%, where the vent would start to spit liquid.
 

dkamp

eMail NOT Working
It seems that many people don't understand why the 80% fill rule exists... so I'll handle that here:

Liquid propane expands and contracts with changes in temperature... and as with all liquids, it is NOT compressible.

When propane in liquid format experiences a temperature rise, it expands. If there's no place for it to expand to, it MAKES a place to expand to... blows valve seals, past fittings, or right through the seam of a freshly broken line.

Another interesting aspect of propane, is that when it's a gas, and pressure rises, propane will change phase... to liquid... and eventually, you'll have a vapor line that's totally full of liquid.

If you fill a tank beyond 80%, there's a very high likelyhood that it will experience a problem from excess expansion pressure... exceeding the test pressure to which the pressure vessel is built.

Also- in order for gaseous withdrawl to occur at a high enough RATE to feed a hungry device, there must be enough volume inside the tank for expansion. On a steam engine, we have a 'steam dome'... which provides enough exposed surface for steam to eminate from the water... same concept applies to boiling propane in a tank.

The vent on most tanks is a combination... vent and level indicator... colloquially referred to as a 'spitter' valve... when you reach the point of it's 'dip tube', you'll get liquid out the valve, not gas.
 

Vanman

Subscriber
Last Subscription Date
07/10/2019
Although I assume it is safe to say that ALL propane tanks have a safety valve. So an overfilled tank that warms up and runs out of space to expand is not going to overpressure the tank. It will lift the safety valve and vent liquid propane. Which is the real potential hazard, depending on where it is when it does it.

Come to think of it, Dalmationgirl had exactly this happen to her, in her living room. Tank had been overfilled out in the snow, then warmed up and went off in the house. There was something of a wild story of hastily rushing it back outside... :D
 

Heins

Subscriber
Last Subscription Date
01/02/2020
When they fill a 100# bottle 80%, they won't let you haul it lying down it the back of a pickup because the safety valve has liquid next to it. The valve won't relieve the pressure fast enough if the propane is a liquid. I have heard of a 100# bottle blowing up in the back of a pickup because it was lying down.
 

Odin

Subscriber
Last Subscription Date
07/13/2019
I think a lot of the 20lb tanks and probably most 100lb as well use a burst disc instead of a safety valve. These are set to the tank's MAWP of 300 PSIG.

The goal is the same- if the tank pressure is getting too high, release some of the tank's contents to lower it. But the big difference is that a burst disc once blown will vent the entire contents of the tank, while a safety valve behaves the same way as such a valve on a steam engine.

Having a 100% liquid fill would indeed result in liquid being forced through the safety valve or burst disc, preventing the tank from blowing down fast enough to avoid a blev explosion in some situations. Being in the back of a pickup truck is one such situation.

I know firsthand that a 20lb propane tank at 70 degrees F, a comfortable summer day, had a tank pressure of 120 PSI. So to get one of these tanks up to 300 PSI it would either have to be overfilled, or be left in a really hot place such as a covered pickup truck bed on a sunny day. Either way when that safety device starts venting, you don't really want to be nearby in case the escaping gas ignites.
 
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