I fully agree that this is normal. This phenomenon is caused by the loss
of pressure across the filter. In spite of the fuel tank level being
higher than the pumps, the pressure between the filter and the pump
becomes low enough so that the liquid fuel turns partially into vapor.
As soon as the fuel/vapor mixture exits the pump, the much higher
pressure causes vapor to turn back to liquid.
The higher the fuel flow, the higher the pressure loss across the
filter. On the 914, when the engine is not running, there is of course
no boost pressure and therefore the fully open fuel pressure regulator
is sending all the fuel back to the tank. This is when the fuel flow
across the filters is maximum. However, when the engine is running at
max boost, more fuel pressure is required and the regulator sends a lot
less fuel back to the tank. Therefore, at high power, the flow through
the filters is greatly reduced and bubbles in the filters is less likely
and possibly totally eliminated.
Regarding the Europa supplied glass fuel filters, I have always thought
that they are too small for the task. The high number of accidents or
incidents due to clogged filters proves it. I strongly recommand the
use of higher capacity filters especially with the 914. Higher capacity
will also reduce the pressure loss and the likelihood of vapor bubbles
in the filters.
Regards
Remi Guerner
Hi guys,
I now have 1250 hours and since new there have always been lots of
bubbles in the
filters.when the pump is running.? All i can do is reassure anyone that
this
is completely normal.? Don't know why but is OK.
Pete Jeffers
-----Original Message-----
From: G-IANI <g-iani@ntlworld.com>
Sent: Sat, 11 Oct 2008 16:06
Subject: RE: Europa-List: Re: Boiling fuel due to underpressure?
Frans
The pumps behave as Gilles described. I have seen bubbles in the pumps
at
any temperature from 0C to 35C on a hot day and with various fuels.
From
experience this is nothing to worry about. The engine gets only what it
needs from the pumps and continues to run very sweetly.
Ian Rickard G-IANI XS Trigear, 200 hours
|