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<I would think that a well-designed fuel system with the pumps located
as low as possible
Instead of speculations, you can actually measure
how good it is. A pump, clear fuel lines, and water instead of fuel. Pinch fuel
line with pliers to increase pressure drop. Watch bubbles come out of
solution. Hear the rattle from pump due to it's inability to flow air.
If you also put a pressure gage on pump inlet, you
can see how fine fuel filter increases risk. You can see how small diameter
tubing increases risk, heat, head pressure, etc etc.
<the result of a forced landing
Egg had one forced landing. It was caused by vapor lock. Absolutely NOTHING
to do with the lack of bleed line. A day later, Jan made it to the crash site.
Pump would not flow fuel until he cracked the line loose. This is simply because
the inlet to pumps was not wet. He did not understand this. He just reacted to
symptoms. Nothing to do with vapor lock. Remember, this was crash site. Who
knows what attitude plane was at. As I described, if you screwed up your
plumbing from tank to pump, then pump is not self priming.
<tested this system on the ground and it works as advertized
You also test it without the bleed line?
FWIW, everything you describe is not vapor lock,
has nothing to do with vapor lock.
-al wick
----- Original Message -----
Sent: Wednesday, August 17, 2011 9:19
AM
Subject: [FlyRotary] Re: Dennis Haverlah
Fuel System...or any others, for that matter.
Al,
I would think that a well-designed fuel system with the pumps
located as low as possible, in a cool area, and a return
system should not be troubled with vapor locking. Although I
guess it could happen in Death Valley in August if the a/c is left out in
the sun for 8 hours, and running auto gas. So far, I haven't had any
problem here in Texas (temps 105* today).
My purpose for installing the bypass circuit was more critical to safe
flight. (The solution was the result of a forced landing, or
two, in an Eggenfellner Subaru installation.) During ground runs,
using a 5-gallon can, I found that the efi fuel pumps could not restore
pressure once the tank had been allowed to run dry. When this
occurred, the EFI pump would suck a big slug of air into the inlet side
of the pump, loose pressure, and being unable to build psi equal to the
pressure regulator setting, it would stop pumping fuel (vapor lock). The
only way to restore operation was to crack open the system downstream of the
pump until the slug of air could be passed on through the fuel
pump. Not sure this meets your definiton of "vapor lock", but I
think it does, but for a different reason than fuel vapor pressure.
I have tested this system on the ground and it works as advertized.
If the tank runs dry, switched to a full tank, the efi pump will restore
pressure to the system within a few seconds. I urge all builders to run
this test on their fuel system to determine whether or not their pumps are
able to restore pressure after running a tank dry. Or, just don't ever
run a tank dry.
Mark S.
On Wed, Aug 17, 2011 at 10:22 AM, Ernest Christley
<echristley@att.net> wrote:
Al Wick wrote:
I'm really concerned for some of these fuel designs. The
fuel bleed has nothing to do with vapor lock. Virtually no effect at
all.
I have a strong, positive head
pressure going into my pumps. They, and the regulator, are about 8"
directly below the tank. Excess fuel goes back to the opposite side of
the tank from the pickup, and a single line goes forward to feed the
injectors. The fuel lines are arranged such that heat soaking the
lines to the point of boiling the gas will push liquid fuel down hill and
behind the firewall, isolating the gaseous gas with its heat at the top of
the line. Turning the pumps on will pressurize the line to 55psi,
returning most of the gaseous fuel back to a liquid state. The ECM is
programmed for a longer clearing pulse on hot start.
The point of the
bleed is to allow fuel to move back to the tank. I had the issue of a
the pressurized lines being perfectly sealed. The pressurized fuel was
finding the path of least resistance out, which just happened to be out the
injector and into the intake manifold where it sat as a little puddle.
Heat soaking the lines would not push liquid fuel downhill and back
behind the firewall. It would push more fuel into the manifold.
A puddle of gas sitting in a composite manifold, just above a hot
exhaust stack is just bad mojo. A poorly sealed regulator allows the
pressure to bleed off in about 5 seconds (give or take), isolating the hot
fuel in front of the firewall, and keeping the rest cool and out of the
intake manifold.
Got nuthin' to do with vapor lock.
--
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