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Seems like the jet pump would get me INTO more trouble than it gets me
out of. Like when I need it least (like not at all) is when I'm at
idle, taxiing with a full bag of fuel. But that seems to be exactly
when it moves the most fuel from left tank to right. Isn't idle when
practically ALL of the fuel pumped from the right tank is bypassed by
the regulator back into that tank? Pretty benign if that's all that's
happening, but all that massive bypass flow is sucking these copious
amounts of fuel from the left tank and trying to cram it into the right
tank which is already full.
Sounds sort of like a sorcerer's apprentice to me ... Jim S.
Ed Anderson wrote:
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
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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
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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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