[T3] Fuel pressure and elevation

[Daniel Nohejl]

If it makes any difference, this is the gauge I have…..one of the liquid-filled ones on the top left:

http://www.mcmaster.com/#catalog/122/591/=13utw0q <http://www.mcmaster.com/#catalog/122/591/=13utw0q>




> On Aug 23, 2016, at 6:43 PM, Jim Adney <jadney at vwtype3.org> wrote:
> 
> On 23 Aug 2016 at 22:21, Max Welton wrote:
> 
>> I think the FPR is composed of a spring, a diaphragm and a valve. Fuel
>> pressure exerts force to overcome the spring. Ambient air pressure is
>> not a factor in this. 
> 
> The spring only about half the force needed in this case. The other 
> half is provided by the outside air pressure. So, in this case, 
> ambient air pressure IS a factor in this.
> 
>> I would think the pressure gauge is also just a spring and a diaphragm.
> 
> Well, sort of, but there's really no spring in a typical gauge. If 
> you put a typical pressure gauge in a pressure chamber, it will also 
> read just the difference between the chamber pressure and the 
> "measured" pressure. It will show the pressure difference.
> 
> That certainly makes this problem harder, since you're trying to 
> compensate for both the change in the gauge and the change in the 
> fuel pressure regulator. The fact that there is a spring in the 
> regulator but there isn't in the gauge means that the two errors 
> don't cancel out.
> 
> I'll have to think about this some more....
> 
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
> 
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