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.
>