Date:         Fri, 30 Jun 2006 14:46:18 -0600
Reply-To:     Steve Williams <steve@CELINEANDSTEVE.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Steve Williams <steve@CELINEANDSTEVE.COM>
Subject:      Re: Charcoal Filter & Valve workings
In-Reply-To:  <e2f6bdb411372.44a54e1c@optonline.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hi,

Tanks for the information.  But I do not understand how the gas tank can
form a vacuum if air is flowing through the cannister.  I have removed
the cannister.  If I plug the large pipe (leading to the valve) and suck
on the small pipe (leading to the gas tank, I can get air from the inlet
at the bottom of the cannister, but it's a tough job.  Should air flow
easily through this path?

Thanks,
Steve Williams

Dennis Haynes wrote:
> The connection at the bottom of the canister goes to nothing, it is the air inlet. You can pull it out of the frame. When the system is working properly, the tank will be at the vapor pressure of the fuel when the van is at rest. The valve is connected to the manifold so it recieves a vacuum signal as the throttle is opened. This open the valve allowing air in. Excess fumes get drawn into the air cleaner to be burned in the engine. The canister shoudl flow air easily. If you can not blow through it, it is clogged.
>
> Dennis
>
> ----- Original Message -----
> From: Steve Williams <steve@CELINEANDSTEVE.COM>
> Date: Friday, June 30, 2006 3:35 pm
> Subject: Charcoal Filter & Valve workings
>
>
>> Hi,
>>
>> I have the classic "clunk" that I believe is the gas tank collapsing
>> from the vacuum.  I know something isn't correct, because when I take
>> the gas cap off after a drive, I get a great hissing as air goes into
>> the tank, and on occasion, I get the clunk.
>>
>> I had my 91 Westy to the mechanic for some other stuff & he had a
>> quicklook at the charcoal filter valve while he had it on the
>> hoist.  He
>> indicated that it was sticking, but got it working again.  Alas, the
>> "clunk" didn't go away.
>>
>> Now that I have a bit of time, I am looking into this myself.  I don't
>> understand the theory of the system though.
>>
>> I BELIEVE the idea is that when the gas tank expands with heat, the
>> vapors are supposed to flow out through the charcoal cannister,
>> exitingat the bottom (when the engine is not running).  Likely,
>> when the engine
>> is running, the vapors should go to the air cleaner?
>>
>> What confuses me a bit is how the system is supposed to work to allow
>> air INTO the tank with fuel consumption.
>>
>> Holding the cannister in my hand, It seems like I can suck & blow
>> any of
>> the connectors & air flows.  It doesn't seem to have any valving
>> insidethe cannister, though the resistance is quite high (but I am
>> using my
>> mouth, remember!).   It seems to me the way that the system is
>> plumbed,air should just come in the bottom of the cannister to
>> equalize the
>> vacuum.  But it can't be that simple..
>>
>> As a proof of concept to ensure the "clunk" is truly the gas tank, I
>> have disconnected the line that runs from the gas tank to the charcoal
>> cannister & put a fuel filter on the end of it to keep dust/dirt
>> out of
>> the fuel tank.  That should allow very easy air flow to the tank and
>> prevent a vacuum from forming.  I know I'll have to be careful to not
>> fill the tank too full.
>>
>> Can someone enlighten me on the theoretical workings of the charcoal
>> valve?  The Bently describes all the bits & testing procedures, but
>> doesn't actually describe the workings of the system.
>>
>> Thanks,
>> Steve Williams
>>
>>