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I used the coarse filter only before the EFI pumps and the
facet pump is between the tanks and the coarse filter. Unless the coarse
filter is filled with debris there is negligible pressure drop caused by
this filter. My EFI filters on the other hand are after the
pumps. But, you are quite right, you don't want any drops in line pressure
that can lead to vapor lock.
Don't know why you don't want to pressurize the
sump. The facet pump only puts out approx 4-6 psi and I can attest, that
additional pressure, can squelch vapor locks between the facet pump and your EFI
pumps. It also helps compensate for the fact that the EFI pumps (as do any
pumps) lower the line pressure at their entrance.
Maintaining pressure in your fuel lines is one of the fundamental needs
especially when the lines are exposed to heat sources.
The recent advent of "Returnless" fuel lines in
automobiles relies on managing line pressure to prevent vapor lock.
Tracy Crook has implemented such a system in his 20B powered RV-8 and
at least on the ground (he has not flown yet), it works fine. Any
system that keeps line pressure up above a certain point will work, any that
permit it to drop below a crucial level at any point will have
problems.
I agree with Al, that from a vapor lock safety standpoint
having wet pumps in the tanks and returning fuel to the larger tanks (as a
heat sink), have proven to the about the best approach. In my case, I did
not want high pressure lines in the cockpit, nor the complexity of
switching both main and return lines when switching tanks (there are other
alternates which do not require switching between tanks - line intra tank
transfers, etc). Like anything else there are trade offs to any
decision.
This is certainly one of the most (if not the most)
crucial subsystems in your engine installation along with ignition. Taking
line pressure measurements as Al Wick suggests is certainly a good idea - then
as, Al points out, you are dealing with a known rather than guessing and
hoping.
Ed
----- Original Message -----
Sent: Sunday, September 09, 2007 9:44
PM
Subject: [FlyRotary] Re: need help
Ed,
You stated that you use Facet pumps, I suppose these are
before the in-line filter. My concern about using the filters before the efi
fuel pump is that there would be more flow restriction. Since I will be using
gravity fed sump tank (5-6 inch elevation difference and I don't want to
pressurize the sump tank), that vaporization could occur; hence I am still
thinking of a large surface screen in the sump tank (already have screen wire
over the strake tank outlets) to catch small stuff that could shorten pump
life, not necessarily plug up the pump. MSD claims to be able to handle small
particles better than the competition. Thinking also of putting in a sight
glass (Plexiglas) to observe tank behavior and screen condition. Can Plexiglas
hold up to auto gas? Oh yes, the sump tank will have a water
catch sub-sump.
Wendell (hope I'm making sense)
I have opened up my coarse filter 6 times in 10
years. First time had some small fragments of sealant used to close
the tank. The next 5 times nothing. Of course, a lot will depend
on type of tank and quality of fuel going into the tanks.
I replace the EFI filters at each conditional
inspection, cut the old ones open and have never found anything in them
either. But, I do use 100LL aircraft quality gasoline - almost
exclusively..
ED
----- Original Message -----
Sent: Sunday, September 09, 2007 4:00
PM
Subject: [FlyRotary] Re: need
help
Thanks Ed,
How often do you have to clean the
filter?
Wendell
I have a fine wire mesh filter in an aluminum
housing with An-6 fittings on each end just before the fuel enters my
header tank.. You can unscrew one end to clean the mesh.
However, been too long ago and I find I never logged the part number on
my fuel data sheet.
But, here are the specific part numbers I use for
the EFI filters
Fuel Filters: OEM Auto Fuel Injector Fuel Filters (Two in
Parallel)
Type: AC GF - 481 Pkg: 25056052 OEM:25055129 (or
equivalent)
Fittings: 3/8 Saginaw to AN6 Adapter, "O" ring required
Ed
----- Original Message -----
Sent: Saturday, September 08,
2007 10:18 PM
Subject: [FlyRotary] Re: need
help
Thanks Rob and Ed for the replys on the MSD
fuel pumps.
Now; what kind of filter do you have
ahead of the pump? I'm thinking of using some fine mesh screen
to make a filter inside the sump tank. It will be hard to
service but believe that one will prolong pump life and possibly.
stop a particle that could interupt fuel flow. What size mesh
is recommended?
Wendell
I have been using the MSD 2225 for
about 20 hour with no problem so far. Plenty of fuel pressure. Only
problem is that it is not threaded so I had to use the barbed
nipples that come with the pump. How bad can that be?
Robert Bollinger
FM1099
MUM
Fairfield IA 52557
(641)472-7000 ex2068
(641)919-3213
cell
rob@mum.edu
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