Kevin Pownall wrote:
>
> I have spoken to three other builders [ two here in Australia ] who have had
> bad experiences with engine starvation. Not every one has had a forced
> landing but they are 'Spooked' by this problem.
>
> The common thread is the puralator filter. They seem to be too fine and to
> have too small a surface area so that when even a little material comes
> along they choke. Additionally the are prone to leak air [ possibly with the
> greater fuel pressure or the 914 pumps this is a new factor].
I'll bet there isn't 10% of the filtration area of a disposable,
folded paper, automotive filter of the same size.
I remember Europa said paper elements bad, as any water can restrict
flow. Sooo, for amusement, I bought an auto unit (small, with 1/4"
nipples for worst case). I drained 16 oz. of fuel through it (2"
average pressure head, simulating almost out-of-gas in the Europa).
Got a computed, 11 gal/hour flow rate. I dried out the filter and
soaked it with water. No change in flow rate!
I then dried and re-soaked it, then froze it down to 17 deg F. (ditto
for the fuel, so it wouldn't thaw the ice). I got about 8 gal/hr flow
rate, initially slow. But at that temp, and in fuel, water is only
slush.
In fiddling with this sealed filter, I notice an air bubble seems
endemic to these things. If you attach a piece of tubing to the
outlet end, and submerge the filter deep in water, the air bubble
still remains. ??? Must have cut that physics class. Anyway, I'm
thinking the Purolator filter is not ingesting air past the gasket
(while not seeping out fuel). The relative pressure of the bubble vs.
ambient I doubt could pull many molecules past an almost leak proof
gasket.
Anyway, I hesitate to re-design my system now, to situate a
gascolator, as she's assembled too far. Plus, I prefer the redundancy
of two filters, as per Europa. I'm wondering if an automotive unit
(with 5/16" nipples) would be wiser on the flight side of my parallel
914 setup, leaving the Purolator on the boost side.
Regards,
Fred F., A063
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