Date: Thu, 30 Aug 2007 19:27:32 -0400
Reply-To: "T.M." <tinkerman007@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "T.M." <tinkerman007@YAHOO.COM>
Subject: Re: Measuring fuel pressure
On Thu, 30 Aug 2007 09:25:56 -0700, Mark Drillock <mdrillock@COX.NET>
wrote:
>keep the gauge raised above the engine so no fuel gets into it and an
>air pocket stays at the gauge.
AFAIK, there are two main types of pressure gauges:
1. incoming pressure goes into a sealed, spiral tube that is connected to
the gauge needle through some mechanism (either directly or a rack-and-
pinion one). Increasing pressure causes the tube to expand and "unwind"
(just like those toy roll-up wistles), which causes the needle to move in
proportion.
2. Air pressure gauges (both the "dipstick" as well as the moving dial
type) usually have a piston inside a cylinder connected to lever that
moves the "dipstick" or causes the dial needle to rotate via a rack and
pinion mechanism. The piston works against a spring, thus linear movement
is proportional to the incoming pressure. This design is much less robust,
often made of plastic and the piston seal is some simple plastic, not
something you want fuel to get into and spray out in case of malfunction.
Many simple air pressure gauges have fallen apart in my hands.
Obviously, the first method is better for fuel and is safer too. I'd of
course prefer a gauge I don't have to keep carefully upright and above the
fuel rails. If it's of the sealed spiral tube type it probably won't be
damaged by the fuel (I guess all fluid pressure gauges work like that) and
that would be preferable.
So I think I'd best get a fluid compatible pressure gauge.
Also, attaching a schreuder (standard wheel air pressure valve) I
mentioned earlier sounds now like a bad idea, as I don't know if it can
hold the 90+ psi possible in fault conditions or withstand the fuel. Only
a hose-to-tube connection with hose clamp sounds safe.
> Never press the release button since that will let fuel get closer to
the
> gauge.
And also might spray out, a potential fire hazzard.
>TinkerMan wrote:
>
>>.... I'm trying to debug as per the Bentley manual
>> but don't have a fuel pressure gauge, and it's hard to
>> find one locally (non at Auto Depot, and I don't know
>> any professional shops), so I'm trying to improvise.
>> Here are a few ideas I've come up with:
>>
>> 1. An air pressure meter - these are quite common (the
>> ones with rotary movement, not the "pen-type"). Of
>> course I need to find one with a 3-bar scale and a
>> screw-on schrueder valve (the standard car wheel
>> valve) with adapter to the fuel pressure test point
>> (the screw on the fuel rail 'T' near the fuel pressure
>> regulator), so I won't have to hold it while measuring
>> (as needed with the cheap gauges which are
>> press-to-test types).
>>...........
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