You're right Dennis (and Mike).  Unless the tank is opened it should not get air inside.  My bad.

Basically what I said was wrong.  I spent a little while educating myself about purging propane tanks.  Seems like the the biggest real life problems from not purging are air/lp mix that doesn't burn well, regulatgor freeze up from the water vapor in the tank, odorant fade and over pressurization (which will go out the relief valve).

The interesting thing I learned is they can't purge a tank at the fill station, it needs to be purged with LP vapor not liquid so it needs additional hookups besides what they have at the pump.  I had a good LP service station do it that way once.  Oh well.

And I have gotten away with not purging a couple tanks I replaced valves on, but I assume after several empty/fill cycles, they were purged.

Feel free to correct me if I'm wrong.

--- On Wed, 10/3/12, Dennis Haynes <d23haynes57@HOTMAIL.COM> wrote:

> From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
> Subject: Re: Propane Tank question
> To: vanagon@GERRY.VANAGON.COM
> Date: Wednesday, October 3, 2012, 6:57 PMYou
> Actually when liquid propane come out
> of the bleeder the tank is only 80%
> full with the required vapor space remaining above the
> liquid. In normal use
> the tank is always pressurized and even if allowed to go
> empty very little
> outside air should be getting in. As compared to a new tank
> that has never
> been filed or may even have some water left in it from
> testing. 
> 
> Dennis 
> 
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]
> On Behalf Of
> David Vickery
> Sent: Wednesday, October 03, 2012 4:30 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Propane Tank question
> 
> I think people are making too much out of purging a
> tank.� When it runs out
> of propane as they often do, it is filled with air.�
> When the bleeder is
> opened while filling the air is expelled out the
> bleeder.� When liquid
> propane starts coming out the bleeder, it is full.
> 
> --- On Wed, 10/3/12, Mike S <mikes@FLATSURFACE.COM>
> wrote:
> 
> > From: Mike S <mikes@FLATSURFACE.COM>
> > Subject: Re: Propane Tank question
> > To: vanagon@GERRY.VANAGON.COM
> > Date: Wednesday, October 3, 2012, 12:15 PM On 10/3/2012
> 11:32 AM, 
> > Stuart MacMillan wrote:
> > > Problems like this are maddening!� Bad auto stop
> > valve or bleed valve that
> > > doesn't vent are the only things that can prevent
> > filling.
> > 
> > It's more likely that the tank simply needs to be
> purged of air, as 
> > already mentioned.
> > 
> > When the tank has nothing but propane in it, it can be
> easily filled.
> > Pumping liquid propane in increases the pressure, and
> the existing 
> > propane gas in the tank turns to liquid, making room.
> For a tank at 
> > 80F, that pressure is about 130 psi.
> > 
> > If you try to fill a tank which has air in it, the air
> simply 
> > compresses, and pressure goes up. New tanks are often
> shipped with 
> > compressed air in them, so you can't push much propane
> in before the 
> > pressure gets too great to be able to pump more.
> > 
> > Hence, the need to purge the air from the tank before
> first use.
> >
>