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Mark said:
<Yes, the test led to the search for a solution
Way to be. Glad you went to the effort to test it. Others might have been
tempted to respond just by cracking the fitting on fuel rail. Fuel starts to
flow: "Took care that problem". You pursued further so that running one tank dry
is not catastrophic.
Top view of your diagram looks good. It's the fine
details that make a difference. Some plumbing oversight prevented your pumps
from getting wet.
I do hope those two inlet filters are coarse ones
with low pressure drop and high surface area. You can't beat the oem inlet
filter bags.
-al wick
----- Original Message -----
Sent: Wednesday, August 17, 2011 11:46
AM
Subject: [FlyRotary] Re: Dennis Haverlah
Fuel System...or any others, for that matter.
Al,
You wrote, "You also test it without the bleed
line?"
Yes, the test led to the search for a solution. You can see the
"bypass circuit" on Egg's fuel system schematic at http://www.eggenfellneraircraft.com/Manual-Updates/EarlyManualFuel.html.
This is what I incorporated into my fuel system, and it solved
the problem. Its been quite a few years now, but I may still
have some of the posts on the Eggenfellner list that occurred
in search for this as the final solution. You wrote,
"FWIW, everything you describe is not vapor lock, has nothing to do
with vapor lock."
As I said, I'm not sure if my condition fits the definition of "vapor
lock", but that's what someone labeled it, and it stuck. The problem is
that EFI pumps don't draw or push air very well. So, if the flowing
fuel is replaced by air due to an empty tank, the pump keeps running, but
essentially stops pumping fuel. With a 40# spring in the downstream
circuit, it is virtually impossible for the pump to pass the air even
though the selector valve has been swiched to the full tank. I
would agree that the fuel injectors should be able to pass the air, provided
the prop is still turning. (This was not the case with my ground test.)
The bypass circuit ensures that flow will be restored as soon as the
bubble passes through the pump and the fuel pump regains its
prime.
Mark S.
On Wed, Aug 17, 2011 at 12:06 PM, Al Wick <alwick@juno.com>
wrote:
<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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