Initial fill of new Propane tank fact or fiction on purge needed

Richard J Kinch wrote:


The "i think" answer was wrong, the question was wrong (or just sarcastic). Explain the explosion potential of air in a propane tank? And, there is no explosion potential in a gasoline tank, the air/fuel ration over the liquid gasoline is too rich to burn. Right at the filler opening is a different question.
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Hey Roy,
The retail supplier of any new 20# tank here will do the required purge, and do it for free. I've never asked why it is done, but II assume that the purpose is to make sure that there is no trapped air inside to cause a problem if it is released into a burner. Lately, places like Home Depot are carrying pre-filled new tanks though.
Take care.
Brian Lawson, Bothwell, Ontario. XXXXXXXXXXXXXXXXXX On Thu, 18 Dec 2003 01:18:53 GMT, snipped-for-privacy@hotmail.com (Roy) wrote:

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snipped-for-privacy@hotmail.com (Roy) wrote in message

I've bought several new propane tanks, they've all had to be purged. You DO NOT want air mixed with your propane in there. Purging amounted to opening up the bleed screw while propane pumping was going on, screw remained open until propane fogged out of the opening. The tanks were then filled to proper weight. I got to pay for the propane that escaped, there was no extra charge for the filling station guy having to use his screwdriver. You got ripped off. On two of the new tanks there was considerable air pressure in the tank before they were even hooked up. The last one I bled down before hauling it over to the rental place where I get tanks filled, took less time that way. It took about 15 minutes for the 60 lb tank to quit passing air after I opened up the screw, there must have been a lot of pressure in there. I suppose they use it for checking for leaks after assembly, probably roll them through a water tank after pressurizing and look for bubbles at the joints. At least being pressurized that way assured me that it wouldn't leak when filled.
You need to find another, more honest, supplier.
Stan
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My understanding is that that is not a proper purging.
Per NPGA bulletin 133-a To purge a container, the following steps should be taken: 1. Purging of containers should be performed in an approved area (see NFPA #58) 2. Determine if the container pressure is zero. Should the container contain only air pressure, the air may be vented directly to the atmosphere through the service valve. 3. If free water is present in the container, it should be drained. 4. Pressurize the container to approximately 15 PSIG with LP-gas vapor. Never purge with liquid LP-gas; to do so will cause the moisture vapor to chill and remain in the container. 5. Fully open the container service valve and vent safely to the atmosphere. 6. Repeat the fourth and fifth steps for a total of five purgings.
-----------
Lane
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Hum - now with the new OPD valve - item 3 requires the valve be taken off. It won't drain out upside down. Maybe through the escape valve - maybe.
Martin
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Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer snipped-for-privacy@pacbell.net
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Eastburn wrote:
>>> 3. If free water is present in the container, it should be drained.

Actually #3 would require the removal of any valve. OPD or otherwise.
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Mark

N.E. Ohio
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You sure it was presssurized with a gas so that it didn't need to be purged?
Stan Schaefer wrote:

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Hey, I'm not sure what gas was in there, I just assumed it was air. Tanks are cheap, you think some manufacturer is going to go out of his way to put CO2, nitrogen or argon in there just to check for leaks? They can't be easily shipped with any flammable gas in there, either, lots of DOT regs on that. No matter, if it doesn't dissolve in propane liquid, you're still going to get excessive pressure build-up. Think what would happen if you took a closed tank full of pressurized air and started pumping in water. It's going to raise the pressure even more, right? Air will dissolve in water a little and I don't know the solubility of gaseous air in liquid propane(and have no real willingness to find out), so the cases may be a little different. You'd still end up getting more pressure in the tank than just what would be generated from vaporizing liquid propane at ambient temperature in the tank. Purging the tank the first time its filled is a pretty easy thing to do to avoid any possible problems.
Stan
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Stan Schaefer wrote:

We are all a little confused (us non-propane dealers). I've had three new tanks recently and none of them were purged the way it says on the tag. One of them gave me a little trouble that eventually went away. All of them cost me about $10 for a purge, nobody here does it for free. Most around here charge a minimum fee which is for filling a 20# tank. But, purging is for safety and reliability of the appliance usage. It has nothing to do with the possibility of the tank blowing up. Air in the tank when it is filled isn't going to increase the pressure over what it would be if filled without any air. After all, the valve is open to atmosphere pressure when filling. And when you use the tank, you use gas, not liquid, so the air comes out which is the problem. At least that's my take.
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On Sat, 20 Dec 2003 02:24:11 GMT, "George E. Cawthon"

Your take is wrong. Due to environmental issues, the tank is NOT vented to the atmosphere when filling by weight. The valve is connected to the filler hose, the valve opened, and the pump started. There is NOTHING in the tank but propane - either in liquid or vapour state. The tank is filled to 80% max capacity with liquid. The other 20% is pure pressurized propane. Now, if the tank is NOT purged, it starts out full of air at atmospheric pressure. It is compressed to 5 atmospheres pressure if below the boiling point of propane, and comprises a flammable mixture inside the tank at some temperature between there and normal ambient. Not likely a big safety issue - but there IS a point where an explosive mixture exists inside a non purged tank.
When the tank is "used up" it does not have air in it if it started out purged - and would have VERY little even if not purged - assuming the valve did not freeze etc. So refilling the tank does NOT require venting. A "brown valve" on a vehicle tank also eliminates the requirement to vent the tank when filling. As soon as the liquid level reaches the bottom of the tube (80% mark) the fuel flow is shut off. Venting of propane tanks at fillup is currently illegal in many areas - as it should be - for both safety and environmental reasons.
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George E. Cawthon writes:

False.
True, eventually.
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Richard J Kinch wrote:

Ok, so I exaggerated a bit since the total pressure is equal to the total of the partial pressures. If you took all the air in the tank at 1 atmosphere and compressed it into the space above the liquid nitrogen (compressed bout 5 times?) the psi would be pretty low and much lower than the propane gas. Since gas volume and pressure are inversely related and one atmosphere .7 psi, the pressure would be 5 x 14.7 or 73.9 psi. So just add that to the pressure of the propane which someone suggest was at least 200 psi. I don't think that has any significance for safety, unless they make awfully weak bottles.

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George E. Cawthon writes:

No, more like 26 psi (0 deg F), 122 psi (70 deg F), or 190 psi (100 deg F).
I suppose now someone will ask, "hey, can I use my propane tank to run my air tools without a compressor?"
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    Sure -- until the first spark. :-)
    A die grinder with front exhaust would be an interesting experience -- outdoors. :-)
    Something else -- indoors -- might be the last thing you do.
    Or -- a die grinder with rear exhaust would really call for Nomex work clothes. :-)
    Enjoy,         DoN.
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(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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Interesting thing I saw with my own eyes..I went with a buddy to purchase a used propane tank one Saturday morning about a month ago. We are under the impression from a source that the tank is left over from a tobacco bulk barn operation. When we get to the place, I could not believe my eyes! It turned out to be a guy who recycles used propane tanks, and he had at least a couple acres of tanks of all shapes and sizes, from camper tanks to multi-thousand gallon ones. As we got out of the truck, we noticed several tanks about 100 feet away with 3 inch holes burned in them with a cutting torch, just sitting there slowly burning off the residual fumes in the tank. Needless to say, this made us rather uneasy. Upon talking to the guy, he told us he had been doing this for over 20 years, and had never had an injury or serious incident. He said as the first penetration is made, there is a whoosh from the tank, then it subsides to a slow burn. They do this all day, every day. My buddy bought a used 350 gallon tank from him for $100 and we went on our way. 123 tanks were $30, and 100 pounders were $10, He throws a regulator in on the deal if he has one at the time. I checked with a local gas company about him and the response was "Yeah, he does all our excess tanks, and everybody else's around". I asked the requirements on them filling a tank like that on home delivery, and all they required was a bill of sale or a receipt to prove ownership of the tank, which around here also gets you a 5 cent discount per gallon. As a side note, I purged a 123 gallon tank and used it with a relief valve and a bottom drain for an extra capacity air tank on my sandblasting rig for about 5 years with no problems. The mercaptan smell went away after a little usage. Sandblasting puts out large amounts of static electricity, also.
RJ
| Voice (all times): (703) 938-4564

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And just where might this fellow be located? I am looking for a l;arger propane tanke and so is my friend, to use for a compressor tank. No one around this area will sell a tank unless its new. Any used tanks larger than 100# that gas companies have are always scraped or refurbed and rented out.
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Eastern North Carolina.
RJ
| Voice (all times): (703) 938-4564

http://www.d-and-d.com/dnichols/DoN.html
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Stan Schaefer wrote:

Wrong. Very wrong.
That was an improper purge, and if liquid was coming from the bleeder valve it was already near or at capacity.

Nope.
The tank had either dry air or N2 in it to prevent air and moisture from entering the tank which would cause rust and odorant fade. You really did yourself no favor by bleeding it off.
Read my previous post on odorant fade, open the link and read the article if my words not good enough.
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Mark

N.E. Ohio
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I said "fogged", not liquid. Low-temperature vapor, not liquid drops. I've done enough gravity filling to know the difference. They fill by weight, kind of hard to overfill if the scale is set correctly. Might be improperly done in your locale or by your standards, though. It DID get rid of the air or gas in there, the actual object of the exercise.

Well, it's between 6-10% humidity here in the summer, the air or gas is venting OUT, so just how is water vapor supposed to be going back in???? It was hauled over to the rental outfit for filling that day anyway. It was just curious to me that there was that much compressed gas in there already.
One of the other posters figured partial pressure on the basis of the initial air or inert fill gas being at atmospheric pressure. It wasn't at atmospheric pressure, for as long as it bled it had to be at higher pressure than that. Can't be all that much higher, though, the DOT, or whatever their successors are, would start getting on them about shipping filled pressure cylinders. Next new cylinder I get, I'll stick a regulator with a pressure gauge on it just for curiosity's sake before I fill it.
Stan
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Stan Schaefer wrote:

Depends on the scale.

I have written allot of stuff here trying to reduce your ignorance. However if you have read what I have posted and are of such little mental capacity as to not understand what has been written by me and in the links I have posted there is nothing more I can do to make you more aware.
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Mark

N.E. Ohio
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