[T3] Fuel pressure and elevation

[Jim Adney]

On 23 Aug 2016 at 12:47, William J wrote:

>  I don't get how air pressure affects the FPR since it's a closed sealed 
> system . 

Assuming FPR stands for fuel pressure regulator, the answer is that 
it's not a closed system. The non-fuel side of the pressure regulator 
has a vent hole to atmosphere. The spring provides about half the 
force needed to hold the fuel pressure in regulation; the other half 
is provided by atmospheric air pressure, which changes with altitude 
and barometric pressure.

So, the answer is that you should set your fuel pressure at low 
altitude on a day that is neither high nor low in barometric 
pressure.

Gas regulators, like those on oxygen bottles and also those that 
regulate your natural gas lines, are designed to give you a set 
pressure difference between atmospheric and the gas. Absolute 
pressure regulators exist, and they work by having a sealed volume 
behind the diaphram. They are VERY expensive.

Sounds like, thanks to Daniel, we've learned a serious lesson here.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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