I have the same system Paul describes. I have not experienced the problem Fra
ns had. But I operate consistently at far higher density altitudes and temps
than described.
Frans, perhaps you are on to something regarding the filters before the pump
s causing vaporization of the auto fuel at high density altitude/temp, and p
erhaps that is the part of the system that is need of redesign. I wonder if t
rying larger filters and fuel lines would mean less resistance and therefor n
o vaporization?
Kevin
PS- it was great to see few Europa drivers at Oshkosh!
On Jul 31, 2012, at 5:51 AM, Paul McAllister <paul.the.aviator@gmail.com> wr
ote:
> Hi All,
>
> I don't know if this helps or not, but in 1000 hours of operation I have n
ever experienced a vapor lock like Frans has described using Mo Gas. I have o
perated my aircraft on days that are 35c ~ 40c, which have included long tax
i runs. My experience may not translate because most of my take off and lan
dings are at around 1000' MSL. On hot days this equates to about 3000' den
sity altitude.
>
> What I have seen is the engine will not start on a hot day after sitting f
or a while and what I do in this situation is to turn the fuel pumps off, st
art 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 pressu
re sensor.
>
> Paul
>
> On Tue, Jul 31, 2012 at 7:38 AM, Frans Veldman <frans@privatepilots.nl> wr
ote:
>
> 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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