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mtmeans
Joined: 12 Jan 2008
Posts: 2
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 Posted: Sat Jan 12, 2008 6:58 am Post subject: Automatic fuel pump backup switch |
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I have an auto conversion project with dual high pressure fuel pumps. The fuel pumps are plumbed in parallel with one way valves and are not happy when running together (stronger pump blocks flow of weaker), ie harmful to switch secondary on during critical flight. Reflexes being what they are during these times I am considering a fuel pressure (or other switch) that could turn on the second pump if first fails. Any suggestions. I tried to search for this exact issue and had problems. Thanks.
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nuckolls.bob(at)cox.net
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| Posted: Sat Jan 12, 2008 7:54 am Post subject: Automatic fuel pump backup switch |
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At 06:58 AM 1/12/2008 -0800, you wrote:
| Quote: |
I have an auto conversion project with dual high pressure fuel pumps. The
fuel pumps are plumbed in parallel with one way valves and are not happy
when running together (stronger pump blocks flow of weaker), ie harmful to
switch secondary on during critical flight. Reflexes being what they are
during these times I am considering a fuel pressure (or other switch) that
could turn on the second pump if first fails. Any suggestions. I tried to
search for this exact issue and had problems. Thanks.
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The Eggenfellner Subaru conversion recommends
the arrangement I believe you're looking for.
Their recommended installation calls for a
pair of pumps, either of which can run the engine
through appropriate plumbing parts . . .
On the electrical side, he suggests a #1, #2, Auto
switch for pump selection. #1 and #2 are self
explanatory. One or the other but not both. The Auto
position powers the #1 pump through relaxed contacts
of a relay that is energized by the closing of a low
pressure switch. Once the relay is energized, contacts
transition to remove power from #1 and apply power to
#2 pump. At the same time, the relay is electrically
latched so that it will not de-energize without some
externally applied conditions (pilot actions, loss of
electrical power) that cause the relay to relax.
I'll be incorporating this feature into an Eggenfellner
version of Z-19 but before that drawing comes out, I'll
refer you to their webite publications at:
http://eggenfellneraircraft.com/ESeriesInstallationGuide.pdf
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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agustafson(at)chartermi.n
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| Posted: Sat Jan 12, 2008 9:09 am Post subject: Automatic fuel pump backup switch |
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deej(at)deej.net
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| Posted: Sat Jan 12, 2008 11:25 am Post subject: Automatic fuel pump backup switch |
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Robert L. Nuckolls, III wrote:
| Quote: | The Eggenfellner Subaru conversion recommends
the arrangement I believe you're looking for.
Their recommended installation calls for a
pair of pumps, either of which can run the engine
through appropriate plumbing parts . . .
On the electrical side, he suggests a #1, #2, Auto
switch for pump selection. #1 and #2 are self
explanatory. One or the other but not both. The Auto
position powers the #1 pump through relaxed contacts
of a relay that is energized by the closing of a low
pressure switch. Once the relay is energized, contacts
transition to remove power from #1 and apply power to
#2 pump. At the same time, the relay is electrically
latched so that it will not de-energize without some
externally applied conditions (pilot actions, loss of
electrical power) that cause the relay to relax.
I'll be incorporating this feature into an Eggenfellner
version of Z-19 but before that drawing comes out, I'll
refer you to their webite publications at:
http://eggenfellneraircraft.com/ESeriesInstallationGuide.pdf
Bob . . .
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Hi Bob,
I'm confused. I'm pretty sure I remember from the Eggenfellner mailing
list that they currently recommend both pumps on for takeoff and
landing, and to turn off one for cruise. On page 51 of the PDF you
reference, I don't see any of the relays or low pressure switches that
you refer to. In the "green" area of the schematic, there are just two
switches, one for each fuel pump, each inline with a 10A circuit
breaker, that are both attached to pin #8 of the "Bus Master Switch".
In the past Eggenfellner had pressure switches in their installations,
but no longer recommends them due to reliability issues with the
pressure switch and the added complexity of the setup.
-Dj
--
Dj Merrill
Sportsman 2+2 Builder #7118
http://deej.net/sportsman/
"Many things that are unexplainable happen during the construction of an
airplane." --Dave Prizio, 30 Aug 2005
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tshankland(at)sbcglobal.n
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| Posted: Sat Jan 12, 2008 5:24 pm Post subject: Automatic fuel pump backup switch |
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The way I handled this was on my 601 HD with A Stratus Suburu was to put
both electric pumps is series. This will cause an addition of pressures
so after the pumps I put a fuel pressure regulator adjusted to 5 psi. in
this way I can run both pumps for takeoff and landing, or any other time
I like and not exceed the limits of the carb. By the way one of the
Fauset pumps required a by pass check valve so that either pump could
operate independently. I looked into various automatic systems such as
sensing the pressure and modulating one of the pumps but this was far
simpler and so far with my 65 hours has been trouble free.
Tim Shankland
mtmeans wrote:
| Quote: |
I have an auto conversion project with dual high pressure fuel pumps. The fuel pumps are plumbed in parallel with one way valves and are not happy when running together (stronger pump blocks flow of weaker), ie harmful to switch secondary on during critical flight. Reflexes being what they are during these times I am considering a fuel pressure (or other switch) that could turn on the second pump if first fails. Any suggestions. I tried to search for this exact issue and had problems. Thanks.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=157617#157617
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Mark Sletten
Joined: 10 Jan 2006
Posts: 43
Location: St. Jacob, IL (Near St. Louis, MO)
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| Posted: Sun Jan 13, 2008 5:06 am Post subject: Automatic fuel pump backup switch |
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As another has pointed out, Eggenfellner Aircraft no longer recommends an
auto-switching scheme for the dual pump configuration.
Regards,
Mark Sletten
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_________________
Mark Sletten
Legacy FG N828LM
http://www.legacyfgbuilder.com |
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