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Freezing Propane Tanks. A Different Solution


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Ambient temperature and humidity affects how much frost you will see (and the temperature will affect how much you can draw before freeze up---in the summer here in NM I can generally draw a tank down till it feels light as a feather. In the winter it will poop out with noticeable fuel left in the tank.)

Note that some places will just give you a "refill" and charge you for a set amount not taking in account how much gas was left in a tank. Others will carefully note how much was used to top off a partial tank. I know this as a local place charged me for a full fill up on a tank I brought in to be topped off. I *NEVER* went back there again! Another propane dealer *always* does it by the gallon filled *and* has a frequent filler deal where I get a free tank of propane after every 4 fills! Much cheaper than an exchange place---though I do visit them when I have a tank going out of date and need a newer one...

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I am usually not one to post replys like this but Brian, you don't know what the heck you are talking about. Not only is your information inaccurate, it defies the basic laws of physics. The whole rep

No I don't take this personaly It's just that I find the level of caution and alarm in this thread incongruous and disproportionate. After years of people talking about warming their small tanks in

I just don't agree with this. What I am doing is really no different than putting a tank in a tub of warm water. I am not heating the tank above its safe operating temp (about 100F) in fact the blow

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If you are "frosting up" everything every time you're running your gasser; you must have money to burn and are very,very lucky. Just because you have "gotten away" with this doesn't make it wise or safe. I've even seen horseshoers put their frosted up 20lb cylinder in front of a running gasser, because they pressure had dropped off.
The frosting up occurs when you are pushing way more fuel than what your system was designed for. You can only burn so much propane in a enclosed space (your forge). If you excede that finite amount, the propane will them combust outside said enclosure; Your forge will Not heat your stock well but heat your work space and not very efficiently. Plus if you are frosting up, the excessive unburned propane will actually cause the temp inside your forge to drop off.

The frosting up does damage to the rubber diaphragm and rubber hose and can initiate leaks at your fittings. Speak with any of the commercial forge manufacturers, any service worker in the propane industry or fire marshal. They'll all tell you it's a, bad thing

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If you are "frosting up" everything every time you're running your gasser; you must have money to burn and are very,very lucky. Just because you have "gotten away" with this doesn't make it wise or safe.


I am usually not one to post replys like this but Brian, you don't know what the heck you are talking about. Not only is your information inaccurate, it defies the basic laws of physics. The whole reply is rubbish and should be chucked into the "listening to this guy is dangerous" bin. A tank getting cold to the point of accumulating frost is nothing to worry about unless all you have used propane for is barbequing steaks. (And that should be done with charcoal anyway.)

Tanks get cold and frost because of a result of the Joule-Thompson effect. As the fuel is drawn out of the tank it is converted from liquid to gas which, as Thomas points out, is an Endothermic process. This causes the temperature of the bottle to go down. Pulling cold propane through lines will potentially cause them to get cold as well. When those lines get cold they cause the air around them to condense on the tank and lines because they are lower than the dew point in the room. Subsequently the condensation may freeze into frost. There is no moisture in the line. Its not even possible in the laws of physics.

I've even seen horseshoers put their frosted up 20lb cylinder in front of a running gasser, because they pressure had dropped off.


Anyone putting a cylinder in front of a forge close enough to heat the bottle is asking for a BLEVE. This is a short term for a Boiling Liquid Expanding Vapor Explosion. Youtube that and you will see why it is bad. The proper way to "thaw" frozen tanks is with a warm bath of water if anything. Personally i just have another tank and switch the regulator and that is that.


The frosting up occurs when you are pushing way more fuel than what your system was designed for. You can only burn so much propane in a enclosed space (your forge). If you excede that finite amount, the propane will them combust outside said enclosure; Your forge will Not heat your stock well but heat your work space and not very efficiently. Plus if you are frosting up, the excessive unburned propane will actually cause the temp inside your forge to drop off.


This is just insane ranting.

Propane bottles are designed to handle a much higher flow than smiths pull out of them but the result is the cooling of the tanks. Its the same effect as that cold spray paint can you might use in the garage. There is nothing wrong with the pressure flow or anything else. Furthermore you comment about the unburnt propane cooling the forge is patently ridiculous. What do you think happens to superheated propane at 1500º in a reducing atmosphere (lack of sufficient oxygen)? Its simple, it exits the forge out the opening and when it slows enough and combines with enough air, it ignites at its stochiometric mixture. You get yellow "dragon's breath" outside the forge. However since the mixture is uncontrolled you produce more carbon monoxide than you do with a good lean burn. To say the unburnt propane cools the forge is just a violation of the laws of physics. The openings in the forge have a cooling effect on orders of magnitude higher than any unburnt propane of whatever temperature.

Furthermore the atmosphere in the forge has nothing to do with the temperature of the propane. When the propane is rich in the forge it means that the burner is not tuned properly. A properly tuned burner will not do this. Propane forges, whether blown or venturi, use a premixed propane at high speed to balance the flame front velocity of the propane. Without premix the forge wouldn't even light. So the adjustment of the burner will change the mix in the forge, not the temperature or even pressure of the forge. Pressure loss (which occurs as tanks freeze) will have no effect whatsoever on a venturi burner as it is designed to suck in the proper amount of oxygen for the given pressure. As for a blown burner, if the pressure drops, the atmosphere will get LEAN not rich.

The frosting up does damage to the rubber diaphragm and rubber hose and can initiate leaks at your fittings.


The temperature you would need to get the regulator to to cause the diaphragm to malfunction is so godawful low that you would have so little pressure in the tanks that you couldn't get the forge to light. Those things are rated to perform in arctic environments which is a heck of a lot colder than the freezing point of water. Assuming you could get the diaphragm that cold and assuming you could still run the forge on that pressure you are getting, the most likely thing is the regulator would malfunction til it thawed. And if you have leaks at your fittings, they weren't tight enough to begin with and they weren't sealed with propane rated sealant. Do you really know the temperature you have to get brass to to change the fittings significantly? What are you burning? Liquid nitrogen?

Speak with any of the commercial forge manufacturers, any service worker in the propane industry or fire marshal. They'll all tell you it's a, bad thing


First of all commercial forge manufacturers are trying to sell a product and so they are not unbiased sources. Secondly they would say that running propane that cold is bad because mostly you are not getting reasonable pressure out of the tanks and thus the forge wont perform properly. The rest of the rubbish you state is a violation of the laws of physics and so I would avoid any forge manufacturer that pushed that rubbish.

I assume you are just trying to help but when you are not an informed source, you should avoid trying to inform others. You can get someone hurt that way and that is the last thing I wish to see happen to anyone on this forum, you included. I'm sorry for being so harsh but I cant in good conscience let your post go unanswered.
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I copied the following from a post I made for someone else who was asking about the propane frosting effect.

"Propane as a liquid has a very low boiling point and just like every other liquid out there is has a latent heat of vaporization, the exact btu per lb depends on the pressure of the liquid and its temperature.

The latent heat of vaporization is the heat energy required to convert a liquid to a gas or a gas back to a liquid. With water at atmospheric pressure (14.7 psi it requires 970 btu per lb and must reach a temperature of 212 deg F to boil. A btu is short for "British Thermal Unit" a single btu is the heat required to raise one pound of water one degree F. If water is held at 150 psi then it must reach 358 deg F to boil and the latent heat is 864 btu per lb, at 1,500 psi it must be 596 deg F and the latent heat is 556 btu lb.

Propane is the same way, the higher the pressure the higher the liquid temperature must be and the less the laten heat is.

With a boiler one uses fire to give the water the energy required for it to evaporate and maintain the temperature required at that pressure.

Propane absorbs the heat from the atmosphere, here are two links to two charts giving the latent heat at different temperatures and the temperature required at different pressures for propane.

http://www.engineeri...ane-d_1203.html

http://www.engineeri...ure-d_1020.html

If one used a 25 lb tank in 15 hours that would be 1.67 lbs per hour, with roughly 155 btu lb that would be 258.85 btu per hour that the propane would absorb to maintain its temperature. If it is supplied with less heat then that it will drop in temperature and as the temperature lowers the pressure lowers and the latent heat required rises!

Propane has a specific heat of .576, so to raise its liquid one degree F it requires .576 btu per lb. This is also how much heat it will give up for one degree F drop.

So if you have 25 lbs of propane liquid at 70 deg F and it drops to 50 deg F then 20 deg F times 25 lbs times .576 then that is 288 btu that would be released. This is making it simple though, because as you draw off propane not only does it require heat to vaporize it but it also takes its heat energy along with it. Put another way if you have 60 lbs propane and you took 288 btu away from it, initial temperature being 70 deg F it would drop to 61.67 deg F. If you had 6 lbs and took away 288 btu then it would drop from 70 to -13 deg F! Which would only give about 15 psi, I don't know if that chart is in absolute or gauge in regards to pressure, absolute is considering the atmosphere and gauge is zero at atmospheric pressure, probably it is absolute.

As you can see from the temperature/pressure chart that I linked to, the lower the temp the lower the pressure and from the other chart the lower the pressure the higher the latent heat. So it is a double down situation, especially with just a little left in a small tank, then any significant draw of gas from it will drop the temperature so much that the pressure will be too low to do anything.

The freezing deal is from the tank walls becoming so cold that they not only condense moisture on them, but they freeze moisture on them.

The simple solution is to place the tank in a bunch of water, that way it can absorb the heat from the water instead of trying to absorb the heat from just the air around it, there is a LOT more heat in water. So in effect you can get the operational aspects of a big tank from a small one sitting in a bit of water."

Caleb Ramsby

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I would like to add that one cubic foot of water dropping 10 deg F in temperature will give off 623.4 btu.

One cubic foot of air droping 10 deg F will give off .169 btu.

That is a difference of 3,689 times the energy given off by the same volume of water as air.

Caleb Ramsby

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It would mean that propane is evaporating IN the lines, it would mean that you are sucking liquid propane through the regulator, which should remind you that a propane tank MUST stand up during operation ! Liquid propane will first evaporate in the reg freezing it up then when the reg will be too cold, the propane will l freeze the hose that will become as breakable as glass and WILL break licking liquid propane on the floor until it will meet the hot gasser (and trust me it will, gaseous propane takes far more volume that the volume of the boiling puddle it evaporates from), with the consequences you can imagine...
If a by a miracle the hose doesn't break you will still have to deal with a frozen ball valve on a mad flame-thrower shooting a 20 feet long flame...
The safety device on the tank valve won't work if frozen up and any kind of ball valve will be a pain to reach and break closed in that king of hell...
But, if you run your tank standing up, freezing won't ever be unsafe, just unproductive...
Here is a pic of a friend's Christmas anti-freezing device :D
43775385.jpg

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My initial problem was with frost, in my opinion, due to the tank being overfilled. My theory is that the tank did not have enough vapor head space and it actually was allowing liquid propane to enter my forge system. Frost completely covered the regulator, line, and shutoff valve during 30 degree weather in less than five minutes. It also decreased flame production during this time, stiffened the hose, and actually continued to “run” after I shut the valve off for what seemed like an eternity, but more like 5 seconds. The valve was new and not worn. However, this is just a theory and since I never tested it again with this configuration I cannot prove it. Also I really do not know if this is even possible.

However, I guess that is what I get for not knowing anything about propane and propane tanks. Anyway after my experience I figured I better learn a bit about this propane thing, so I did some research and here is what I found out. If I go by weight and what the manufacturers say my 40lb tank is rated to hold 9.4 gallons of propane, so I weighed the filled tank and it came in at 79.2lbs. According to most sites a 40 lb tank empty, should weigh around 29.5 pounds. Subtracting the tank weight from the total leaves 49.7lbs for the propane.

Obviously 49.7 is overfilled, since it was only a 40lb tank. A gallon of liquid propane weighs 4.24lbs, so that means 11.72 gallons of propane were in my tank. This made some sense to me, because when I took the tank in to be filled it still had some propane in it. When it was at the filling station they put in 11.3 gallons, I saw the meter, paid the bill and have the receipt.

OPD valves are designed to prevent the over filling of a tank. My tank has one, and I guess is not working, since it did not shut the tank fill off at 80% when it was being filled. The capacity according to the manufacturer is 9.4 gallons and if this 80% of the actual volume or where the OPD shuts off, then entire inside volume of the tank, if my math is correct, should be 11.75 gallons. 11.72 gallons actual, is/was just way too close to 11.75 internal volume limit to be safe so I looked for a safe solution to my problem. The store I originally filled it at was closed January 2nd for the observed holiday and I wanted this taken care of ASAP!

Propane is stored as a liquid under pressure. It boils at -44F, those of you who live in Alaska could actually see this happen I guess but where I am from we never get that cold. Anyway, since the pressure or really vapor pressure is what keeps it liquid in the tank, it only makes sense that pressure in whatever tank it is in, would remain the same. This means that a 20lb propane tank is subjected to the same pressure dynamics that a 1000lb propane tank is, if I understand that correctly.

So my quickest solution to an overfilled tank was to buy a two tank manifold kit from the neighborhood Tractor Supply $29.99. I figured this was a win-win situation, if I have to trash the 40lb tank because of a faulty valve I can easily find 20 pounders in the future and I could use the manifold to solve my current problem. I hooked the manifold up to an empty 20lb propane cylinder and the 40 pounder. Then I just cracked the 40 lb valve and left it slowly equalize the pressure in both tanks, about 5 minutes untill it stopped hissing. When I was finished I figured the 40 lb tank would be a little lower and the 20 would be pressurized with just gas, if the 40lb just boiled off. However, the 20 lb tank now has liquid propane in it, bringing me back to my first theory that started it all, -the overfilled tank was indeed flowing liquid propane into my regulator, lines, and fuel rail of my forge. If it were not, then the level of the propane would have been too low in the 40 lb tank to flow liquid propane to the smaller 20 lb tank when it boiled off to equalize pressure, I think.

Anyway after tapping some propane off I disconnected the 20lb tank and set the forge back up with the 40lb. After pressurizing the system and testing for leaks, I fired the forge up and ran it at 7lb of pressure for 30-40minutes, no frost at all. The final weight of the 40lb cylinder after draining and running it for that amount of time is 72.6lb. I know that means that it is still in overfilled condition but is has got to be safer at this point. I plan on running the tank until it is empty and then taking it to an actual propane dealer and having them recertify the tank or condemn it.
I will end this with the following:

This is what I have concluded from various manufacturers’ websites and other web resources. I do not claim to be an authority on anything related to propane, I am only a user. I have learned a valuable lesson I hope to share with others when dealing with propane. That lesson is to buy a new tank and fill it at a reputable place that specializes in only propane.

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  • 1 month later...

I'm pretty new to getting tanks filled, I used to just turn em in because it was faster, but now I have more than 1 so It's way cheaper and easier to fill them. I filled my tanks for the first time yesterday and I noticed the operator of the filling machine used a screwdriver to turn a screw (opening a valve I assume) and when the vapor vented he turned off the machine.. Perhaps the filler at the store you went to did not turn that screw on your tank and thus made it possible to overfill it. Maybe the tank's OPD is not broken but the person at the store did not understand how to use it. I hope your tank is still in good shape!

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i didnt read much of this thread here but is any one here familiar with the rule of 1/7th's. stating that you should never use your lp, acetylene or what ever gas at more than 1/7th its total bottle capacity an hour. so if your set up would empty your tank in about seven hours than your bound to get freeze up.

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The 1/7 rule ***only*** applies to acetylene cylinders, which are unique in fuel gases. They are packed with a porous matrix and the acetylene is stabilize with liquid acetone, which can get drawn up into the regulator if you pull too much gas too fast.

MAPP, propylene, LPG, etc do not have that restriction, because they are built differently. Any gas bottle can freeze up if you empty it too fast, temperature drops as volume expands. That is why CO2 fire extinguishers make such great instant beer coolers. :rolleyes:

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  • 4 years later...

I built a couple of Dave's burners after watching his youtube video. Built a box horseshoers style forge body with 2" of k wool and ITC100. I slowly fired it to cure out any moisture and put it to work. Well, it flat out is a welding machine. using minimal Iron Mountain flux. I have stuck more welds on the first try in this forge, than any other gas forge in decades. Now the PROBLEM; it takes between 15 & 20 psi to get this forge to that yellow welding heat and those burners draw propane so fast, a they will frost up a 20lb cylinder in 10min, 30lb cyl in 12min, a 40lb cyl in 20mi and a 100lb cyl in 30 min or less. Is there something not right in adjustment? Am I expecting too much? What do you say Dave?

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pressure is a trivial issue which has been discussed here many times.   Size of box to be heated is an issue as well as how quickly the gas exits the box. 

I use industrial regulators and smaller orifices than some designs.  I have run as High as 30 psig.  However, from the rate of gas usage you are suggesting it appears that you have made some very fundamental design errors. I suggest you re-read  the stickies for the forge section.

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I don't believe Dave's been a member here for some time now, try his website or maybe searching out his contact info. What size burners and what volume forge? How large is the door is it open?

Running virtually any properly tuned 3/4" naturally aspirated burners at that much psi is going to frost your 5gl. tank up pretty quickly. I keep a 40lb. 10gl. in a water bath to keep them from freezing if I fire two burners at once. If I run more than 2 I'd better have them hooked to the 100lb. tank and that one will frost up in 4-5hrs.

Frosty The Lucky.

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I  guess my problem stems from the fact I've been running a blown Mankel gas forge since 1974 and never dealt with frosted tanks/diminishing pressure (unless the tank was nearly empty and 90% humidity/90f) before. so as a newbie with atmospheric burners I was unaware of their limitations. I tried lowering the psi to the 6-8 that I running my Mankel and never got nearing a welding temp and barely into a good forging temp. I forgot to measure the internal cubic inches, but will later today. So will a larger or smaller C I reduce this frosting up? the burners have .023 mig tips, would changing that help?

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0.023" jets? 1/2" burners and you're icing up even a 20lb. tank? You have SOMETHING built incorrectly to demand that much draw.

Dave's burners are much better inducers so they use larger jets for a proper ratio and significantly more BTU output.

1/2" burners work a treat in bean can or 2 brick forges but not much larger.

Frosty The Lucky.

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People generally have normal mental distortions regarding area when given diameter of orifices.  Just to put it in numbers, a .035 orifice has 2.3 times the passage area that the .023 tip does.  Actual flow through an orifice is a little more complex than a simple numeric comparison but at least it gives something to think about when in one's head .035 is only *percieved* as being about 1.5 times the size of the .023.  

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I'm sorry to be a pedant because Kozzy's point is well made.

Comparing orifices, a .035" diameter orifice does indeed have have 2.3 times the area of a .023" diameter orifice.

However, when comparing MIG tips, they are sized on the nominal welding wire diameter they are intended to be used with. When I've measured MIG tips, all have tended to have a hole size about .006" larger than the nominal wire diameter. A .023" MIG tip will therefore have a hole diameter of .029" and a .035" MIG tip will have a hole size of .041". 

Comparing the hole areas, the .035" tip has almost exactly double the area of the .023" tip and will flow twice as much gas at the same pressure.

If you wanted to turn down the pressure to get the same flow from the .035" as from the .023", you would need one quarter of the pressure: flow through an orifice varies with the square root of the pressure difference. 

It's not just about gas flow though. You also need to get enough air in to burn the gas.

Going to a smaller gas jet reduces the gas flow in direct proportion to the area, but has a much smaller effect on the air flow and therefore effectively leans off the mixture.

The air:fuel ratio affects the flame temperature and I've seen more forges that will not make temperature because they are running too rich than because they are running too lean.

If you have Dragons Breath (a sign that the burner is running rich) and are not reaching welding temperature, it's almost always worth trying a smaller gas jet.

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