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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Propane Tank Purging
Date: Mon, 07 May 2001 22:37:54 -0400

Robert Carr wrote:
> Thanks to everyone for their inputs.
> Well so much for purging the new propane tanks. Took them to an outfit
> that seemed to be aware that something should be done on new tanks.
> The tanks, as purchased had been filled with something, I suspect
> plain old air(no odor). The filling attendant let those air
> kilopascals escape and then proceeded to fill the tanks with propane
> kilopascals,  as normal. No special action was taken, in regards to
> purging. I suspect that I am in the same state, with a first time
> fill, as I was 4 years ago when I bought the trailer.

You're just fine.  Most (all?  At least the Manchester factory near
here run by another John De Armond) tanks come slightly pressurized
with dry nitrogen.  As long as the tank was not open to air, the
attendant's procedure is just fine.  Most of the nitrogen was vented
either by the pre-venting or the side vent.  The rest flowed out
with the first gas usage and went up the burner stack along with the
nitrogen in the air.

When I was in the business, the official procedure was to add some
anhydrous methanol to absorb tramp water to any tank whose status
was unknown.  Since your tank was new with the seal on the valve,
that was an unnecessary step.  I never really understood the purpose
of this since propane from the tanker tends to be wet.

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Propane
Date: Tue, 08 May 2001 00:10:35 -0400

Traveler wrote:

> Question, is propane measured in weight or gallons?  Or both.  I asked a
> dealership and he told me the propane cost $2 per gallon.  He said it was
> their cost.  I have a Class C Motor Home and it has a tank that lies on its
> side and look to be about double a 20 pounder.  A 20 pounder I have for my
> BBQ and I paid $9 for a fill on it.  Would someone like to clarify it for
> me?  Is the measurement different for tanks that cannot be removed from the
> rig?  I would assume they would but just want to be sure!  TIA

It's sold both ways.  The smaller tanks are filled at a flat rate
that encompasses the cost of the propane and the labor.  The prices
are listed according to tank size in pounds so people tend to
associate "X" pounds with "Y" price.

For fixed tanks, including the ICC RV tanks that attach to the frame
are filled in gallons.  Said tanks are also sometimes referred to in
pounds capacity but since the tank is permanently mounted, it is
impossible to fill by weight.  My ICC tank is an 80 pounder, for
example, and it holds something like 18 gallons, as I learned Sunday
when I ran out. :-(  I have a fill station at my restaurant but I
forgot to check before I left.  BTW, I paid $1.49 a gallon at the
Flying J on I-75 north of Atl.

Technically, all tanks - ICC or DOT - are rated in water capacity.
If you look on the ring or nameplate, you'll find two numbers, a
"TW" and a "WC"  The TW is the tare weight or the empty weight.  The
WC is the Water Capacity in pounds.  Arcane?  Yep.  but it is


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Propane
Date: Tue, 08 May 2001 02:04:01 -0400

Kenneth Shelton wrote:

> Weight would be most accurate, because the heating value would correspond to
> the weight.  The temperature of the propane would be irrelevant.  I'll bet
> that the dealer buys it by weight, maybe by using conversion tables that
> relate to the temperature.  When I bought ship's fuel, we always converted
> it to a standard volume at 60F, then adjusted for the specific gravity of
> the particular load for the billing.  Of course, I'd be signing a receipt
> for $400,000 to $500,000.  Accuracy made a difference here, 'cuz we burned
> something like a million gallons every five weeks.
> All the vendors I know, including the truck that fills the tank at my house
> have meters that measure the volume, i. e., gallons.

All propane meters certified for trade are temperature compensated.
You'll note the little label on the dial if you look for it.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Propane Tank Purging
Date: Wed, 09 May 2001 14:06:00 -0400

Chris Bryant wrote:
> On Tue, 08 May 2001 00:16:22 GMT, George E. Cawthon wrote:
> >My new BBQ tank came with tape across the valve and said it needed to be
> >purged.  I asked the guy about purging when he was filling and he just
> >said that's why the (side) valve was open.  No repeats, no nothing just
> >filled it.
>         I found a pretty good page with methods and reasons:

Let's discuss this a bit.  The first thing to realize is that this
procedure is for purging large fixed tanks.  It is quite uncommon to
open any sort of vent while filling a large tank.  Under those
conditions, the web page is right - the air would be trapped and
would increase the pressure in the tank (law of partial pressures)
and would probably cause the tank not to fill completely, since most
propane liquid pumps max out at about 50 psi or so.  Since it is
standard practice for portable and ICC tanks to fill with the max
fill vent open, this situation does not occur.  I actually
experimented with this years ago when I owned the welding gas
distributorship.  The pressure in a new 20 lb tank after filling is
within a couple of psi of the vapor pressure, indicating essentially
no air.

As for water hydro, that is true as far as it goes but the modern
practice is to dry the tank afterward.  Part of the "hydro" is to do
a visual inspection of the interior of the tank and any visible rust
is cause to reject it.  No manufacturer would take the chance of
rust by leaving water in the tank.  I know for a fact that the tanks
manufactured in nearby Crossville, TN are shipped with a dry
nitrogen fill because I used to occasionally visit when my cousin
was the plant manager.  Since dry nitrogen is so cheap and since it
positively protects the tank from rust, I'd be quite surprised to
find that this isn't a universal practice.

The recommendation to put some methanol in the tank is primarily to
trap out water that sometimes comes with the propane.  Most, and
probably all propane is fairly wet as it comes from the refinery.
New tanks are particularly susceptible to rust because they've not
had a chance to passivate while in contact with the propane and
they're not coated on the inside with the oily mercaptin residue.

Adding methanol to propane tanks gives me great concern because
methanol is so corrosive to light metals.  I know for a fact that it
will corrode the aluminum used for gas plumbing inside gas
appliances.  If we pay attention, we've probably seen the white
corrosion products inside aluminum piping.  My suspicion is that
methanol vapor is  contributor to this.  My practice was to evacuate
the new (large) tank and then use only a tiny bit of methanol.  I
probably would not use any now if I was still in the business.

As far as their multi-step purge procedure goes, I could never
imagine using that.  First, wasting that much propane is silly,
especially at the current price of propane.  Beyond the cost is the
problem releasing that much propane might cause.  I've had the FD
called to report a gas leak by neighbors while filling my MH tank
bleeding only through the max fill vent.  I can't imagine dumping
that much odorized propane in any sort of populated area.  This is
particularly silly considering that one evacuation which would take
less time than multiple purges, will do the trick.

As with any trade, the particular conditions will to a great extent
dictate specific practices.  I had a pretty good supplier who
supplied pretty dry propane.  I never had water problems.  A
competitor was just the opposite.  In years past, ammonia was a big
contamination in propane in agricultural areas because propane
trucks used to be used in the summer for delivering anhydrous
ammonia fertilizer before DOT banned the practice.  Dealers in the
affected areas developed tests for same.

 I know that it is going to be hard for some of the arm-chair
experts in this group to accept but more often or not, most people
in the trade have a good idea of what they're doing and why.  No,
the pump jockey probably doesn't but the person who sets the
procedures for the facility usually does.


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