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
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.
On Thu, 18 Dec 2003 01:18:53 GMT, firstname.lastname@example.org (Roy) wrote:
email@example.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.
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
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.
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.
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.
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
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.
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.
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. :-)
Email: < firstname.lastname@example.org> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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.
| Voice (all times): (703) 938-4564
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.
Visit my website: http://www.frugalmachinist.com
Opinions expressed are those of my wifes,
I had no input whatsoever.
Remove "nospam" from email addy.
Wrong. Very wrong.
That was an improper purge, and if liquid was coming from the bleeder
valve it was already near or at capacity.
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.
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
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.
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
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