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George, its actually a siphon pump for a two tank
system. They use the fuel being released by the fuel pressure regulator in
one tank and run it through a restriction ( a Ventura) and it flows through
the Ventura (returning back into the main tank) it develops a low pressure,
this low pressure region of the jet is plumbed to the second tank. The
"suction" action pulls fuel from the second tank into the main tank where the
EFI pump, "Jet pump" and fuel pressure regulator are all located. This is
used as a "transfer" pump but does not require another "electric" pump such as a
facet pump that many of us use as either a boost pump or fuel transfer pump.
Interesting concept for sure - but if for some reason something would break the
"siphon" effect (say trash in the Ventura) then NO fuel transfer from the second
tank. But, then a transfer pump can fail as well - sigh nothing never
breaks {:>)
Hope this explains it well enough.
Ed A
----- Original Message -----
Sent: Monday, February 14, 2005 9:01
PM
Subject: [FlyRotary] Re: Fuel System
Design - Jet Pump
Mark/Ed,
What's a Jet pump?
George ( down under)
Good Idea, Mark
I think that people get pretty hung up and
adamant about certain things - even though they may indeed work. While
all fuel systems clearly require careful design and construction attention,
some appear to require even more scrutiny. What I think sometimes gets
folks in trouble is they "copy" a design they have seen/hear works.
However, they seldom ever copy the design faithfully either due to
space/configuration constraints - or they have an "improvement" to it.
The bottom line is the system has changed, "Yes, Virginia, it may really
matter as to whether the pickup is at the top vs the bottom,
etc. ".
Even Tracy's system can byte you if you are not
careful. You must pay attention to fuel transfer or you can
end up with the return fuel pushing out the vent of the return
tank. So while I do believe his design eliminates (or certainly
diminishes the chance of vapor lock) - you now must carefully
monitor how much fuel is in the return tank. I believe Tracy
uses a facet pump to move fuel from one tank to the other - which even
though unlikely, could fail leaving fuel unavailable. I would
have to agree though that scenario certainly would leave you a bit more time
to consider your options - than a faltering engine on take
off.
But, yes, it would appear that the "jet
pump" might indeed be a replacement for the facet pump. Interesting
concept.
Ed A
----- Original Message -----
Sent: Monday, February 14, 2005 4:40
PM
Subject: [FlyRotary] Fuel System
Design - Jet Pump
Ed,
Thanks for that excellent
article on fuel system design. In reading through it, on page 5, I
came to the description of the jet pump and had a thought (that alone is a
scary thing). I was thinking that this could be used to eliminate
the need for the facet pump in a design such as Tracy’s which would
simplify things even more than Tracy’s system already does. Of
course, as in Tracy’s design, this would eliminate the
need for the fuel selector valve too. As it was designed to do, the
Jet Pump would be powered by excess fuel from the main fuel pump located
in the left tank. Fuel from the other (right) wing tank would be
drawn into the main (left) tank by the Jet Pump. To prevent
overfilling the main tank, transfer could be controlled by a small
solenoid valve. Since you would be drawing fuel from the right tank
pretty much all the time, it may be possible to route the return fuel to
the right tank. I guess this idea could also be used with a sump
tank. Time for a sanity check.
Mark S.
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