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Ed,
The reasons for not wanting to pressurize the sump tank are
1) don't want a pressurized tank inside the aircraft
2) making a leak proof fiberglass tank is difficult and
don't want to make it harder, although it shouldn't leak
under any contition - just don't like the idea to pressurize
it as of now.
3) two more parts to go bad.
4) more cost
The sight glass is for checking condition of screen filter.
If I could figure out a good way to put the efi pumps inside
the sump tank and get a good seal, that would be my
preferred way to go. I could use a barb fitting to go thru
the tank for the pressure line, but still need a large
removeable accesss hole to install and service the pumps.
Auto pumps go thru the top of the tank and have little
pressure to seal against (usually a slight vacuum). My sump
could be thought of as the bottom of the tank - any leak
would empty the main tanks. Any leaks that develope in time
should be small and the smell would let it be known due to
the sump location. Maybe I should go with an aluminum sump
tank and use a good sealant for access ports.
I tested the flow of the fuel line before I closed the
strakes and believe the flow at worst condition of less than
2 gallons (about and inch of water in the tank) and think
the flow rate was about 12 gph. This was with no filter
except the coarse screen in the tank. So 2 x this would
give 24gph and one would never want to take off with only 2
gal. in tanks. From this test I felt that no extra pump
would be needed to keep down vapor formation. Would the
filters you are talking about work in this installation of a
gravity feed? They are neat.
Wendell (still figuring)
>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 -----
> From: Wendell Voto
> To: Rotary motors in aircraft
> 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 -----
> From: Wendell Voto
> To: Rotary motors in aircraft
> 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 -----
> From: Wendell Voto
> To: Rotary motors in aircraft
> 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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