Hi All,
I don't know if this helps or not, but in 1000 hours of operation I have
never experienced a vapor lock like Frans has described using Mo Gas. I
have operated my aircraft on days that are 35c ~ 40c, which have included
long taxi runs. My experience may not translate because most of my take
off and landings are at around 1000' MSL. On hot days this equates to
about 3000' density altitude.
What I have seen is the engine will not start on a hot day after sitting
for a while and what I do in this situation is to turn the fuel pumps off,
start the engine and then turn the pumps on.
I have a single gascolator, with dual pumps + check valves in parallel and
this sits under the baggage bay. I also have a UMA differential fuel
pressure sensor.
Paul
On Tue, Jul 31, 2012 at 7:38 AM, Frans Veldman <frans@privatepilots.nl>wrote:
>
> 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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