On 07/31/2012 12:41 PM, rparigor@suffolk.lib.ny.us wrote:
> It was Decalin, I just did a quick search and found a pretty good
> article you may want to read,
Good article indeed!
> http://contrails.free.fr/engine_914_fuel_syst_test_en.php
This web page mentions "air" in the filters, which should be "fuel
vapor". This is caused by the pressure drop in the fuel filters due to
the flow resistance. The fuel pumps not only increase the fuel pressure
at the output, they also decrease the fuel pressure at the inlet.
As we all (should) know, lower pressure lowers the boiling point.
So, to get rid of the bubbles, you have to prevent the pressure drop in
the fuel filter and/or pump inlet.
One way of achieving this is to install a pre-pump directly at one of
the tank outlets.
I found some interesting pumps at ebay for a low cost (35$). They have
no diaphragms or other rubber or wearable parts but just a piston pulled
by a magnetic coil. If the pump stalls it is just a go-through.
Alternatively one can make a bypass with a check valve. The pumps
deliver 5 GPH, enough for a Rotax, at a pressure of 2 PSI. The pressure
is enough to cancel out the pressure drop of the filters, valves and
hoses and pump inlet, and thus prevent the formation of bubbles (or
vapor lock in more severe cases).
Frans
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