The following is a report of convoluted experience which has been
shortened=0Aby
removing the flight dramatics for those of nervous dispostion.
The Europa's Purolator fuel filter after the main tap will obviously stop
the=0Aengine
in flight if it clogs. While the maintenance schedule demands "check=0Afor
leaks", one might be forgiven in thinking this is for fuel leaking, which=0Ais
easily observable, (or smellable).
My problem(s) arose from the design of this filterr which has
a=0Acleanable/renewable
element. The O-rings contact a glass tube with rounded=0Aends and alignment
is not guaranteed. The very act of re-assembling it can=0Aleave you with
a tiny leak. Fuel egress does not take place through a small=0Aleak due to
a combination of viscosity, surface tension and the fact that=0Athere is zero
or negative pressure difference between inside and outside. But=0Aair can be
sucked in during flight. It might be thought that it would just=0Abubble up
to the top of the float chamber and have no effect, but in fact a=0Abubble can
grow steadily towards the input of the mechanical pump until it=0Afails to
operate.
It is this delay that nearly led to disaster as it could=0Anot be detected
during the normal ground running, and was confused with the=0Aundoubted presence
initially of fuel contamination.
After two occurrences, with factory and PFA agreement I moved the filter
from=0Athe
outlet of the tap to the main outlet from the tank, and added a=0Apermanently
sealed type (=A32.70) in the reserve side, so that it can be=0Aswitched in
during flight. Indeed this action prevented another incident.=0AI am eternally
grateful to Graham S (for Sage?) who pointed out the=0Apossibility of an air
leak as the cause.
I would suggest that whenever this type of filter is re-assembled, the
simple=0Atest
of running the output of the electric pump through a clear tube should
be=0Acarried
out. This shows up such a leak as a fine stream of bubbles. The use=0Aof
two fully sealed types (which have bigger area anyway) gives immunity=0Aagainst
an air leak or clogging.
Graham C G-EMIN=0A
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