Non-linear fuel pressure reg - #2

[Mike Pitts]

>>Could I change the spring to a lighter spring with 
>>a faster rate to alter the regulator's rate...

>I do not understand how you intend to get a "faster rate" from 
>a "lighter" spring?????

I may not understand or use the terms correctly, but here's 
the hypothesis which prompted my question.

The fuel pressure is lowered by vacuum on the top side 
of the diaphram.  This is the same side the spring is on.  
The pressure of the fuel is on the bottom side of the diaphram.

Every unit of vacuum lowers the fuel pressure by an equal 
amount.  So, vacuum compresses the spring.  My assumption 
is that if I make the spring *easier* to compress, the same 
amount of vacuum will raise the diaphram farther and result 
in even less fuel pressure for a given amount of vacuum. 

But then it occured to me, the diaphram surface area on which 
the fuel presses against, and the surface area of the vacuum 
side of the diaphram is equal.  So the vacuum is probably just 
acting as a delta to the fuel pressure only, not the spring, and 
the spring is probably just setting the base pressure.  In other 
words, a faster rate spring will simply compress more from the 
fuel pressure alone, then the delta created by vacuum will remain 
the same.  So I guess there's a good chance that using a spring 
of a different rate won't make any difference.

I know nothing about fluid mechanics, so please bear with me. 

After staring at this cut apart regulator some more, it occurs to 
me that I can easily decrease the surface area on the fuel side 
of the diaphram by making the return oriface much larger.  The 
area of the diaphram (on each side) is approx. 1.6 sq/in.  If I 
could reduce the area of the fuel side to 0.8 sq/in, will I achieve 
a 2:1 ratio??  Or is there a square or square root in there 
somewhere that means I can get a 2:1 ratio without halving 
the surface area?

Thanks,
-Mike
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Mike Pitts
Delray Beach, FL
mpitts at emi.net
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