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Date:         Mon, 28 Feb 2005 10:54:19 -0800
Reply-To:     Pensioner <al_knoll@PACBELL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Pensioner <al_knoll@PACBELL.NET>
Subject:      Re: Filling from a 40-lb propane tank?
In-Reply-To:  <200502281804.j1SI44w4001224@mtac2.prodigy.net>
Content-Type: text/plain; charset="iso-8859-1"

Always wondered how they fill those 16oz portable tanks. Clearly there is a Schrader valve device in the top of the cannister. However my attempts on a dead empty cannister to make that schrader valve release by using the same techniques one would use on a schrader tire valve have never worked. We know that the production facility that fills these doesn't do it by hand.

Now the process for filling propane tanks is the same for any size. The tank MUST NOT be filled beyond 80% of capacity. Here's why. Propane has an expansion coefficient that will cause a tank to RUPTURE (for you CT, that's blow up) if the temperature of the liquid is raised sufficiently to completely fill the container. Much like freezing a soda can. The 80% 'head space' is to allow for thermal expansion so you DON'T rupture the tank. You'll notice the fill level valve on the westy tank is about 80% up the side of the tank from the lowest point. If you attempt to fill the tank to more than that you run the risk of rupturing the tank. So when that valve, which you open BEFORE you start filling emits liquid (white) LPG shut off the fill. The Autostop has a sensor that detects the liquid gas and shuts off the filler. It also as a manual relief valve in the form of a knurled knob on the RH side of the of the autostop. I always open this knurled knob valve before turning on the fill. Manual fill valves require a separate overfill/relief valve at the 80% level that MUST be open before you start filling.

Same for portable tanks in most of the world. Relief valve must be opened before filling. The relief valve has a tube that goes ~25% of the way to the bottom of the tank. When liquid comes out of the relief valve the tank is 'full'. Turn off the fill. Leave the relief valve open until only gas, not white liquid, escapes. Now the tank is at the rated fill level.

With the bodies stacked like cordwood along the highways, a more fool-resistant method, the OPD Overfill Prevention Device incorporating a float that shuts off the fill when the float rises to the ~80% level was introduced. You will no doubt notice that since the introduction of the OPD requirement we rarely see the cordwood anymore.

Propane is dangerous stuff. If you refill your own containers with liquid propane BE SURE you are DEAD CERTAIN that you have sufficent headspace after the fill. Else your van or garage may resemble the federal building in Oklahoma City.


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