| Charlie,
Good points. I mounted my pumps on the floor as low as I could get them, just downstream of the Andair valve. With the dihedral built into my wings, they are below the fuel level. I've never had any problems with vapor lock, and I fly in some pretty hot air. I like the idea of mounting the pumps in the tanks, except for the maintenance issues it creates.
Mark On Sat, Aug 13, 2011 at 8:06 AM, Charlie England <ceengland@bellsouth.net> wrote:
The really frustrating thing about all this is that every
installation is different (not to mention that it's only speculation
as to what caused this particular power loss).
Sixties-era cars (carb, engine mounted fuel pump) had vapor lock
problems all the time in hot weather. Modern cars, almost never
(in-tank high pressure pump). Keeping the pumps as low & as
close to the tank(s) as practical would seem to be the best path.
Van recommends mounting pumps on the floor in the cabin. That means
that the max lift would be maybe 3-4 inches, through a -6 line, and
nowhere near the high under-cowl temps. There's a guy flying an
injected Lyc on ethanol-laced mogas who never has a problem with
vapor lock. He removed the mech pump and uses wingroot mounted
electric pumps.
If it weren't for the maintenance related inconveniences, I'd
seriously consider in-tank pumps, as others have done.
But we still don't know whether this is what caused the recent power
loss....
Charlie
On 08/13/2011 06:20 AM, Ed Anderson wrote:
I should have added - the best overall
approach - returning hot fuel to the heat-sink tanks and
drawing new cooler fuel into the lines.
Ed
Sent: Saturday, August 13, 2011 6:47 AM
Subject: [FlyRotary] Re: vapor lock
Ok, Finn, that was my guess as well.
That then brings up a question - my
understanding of "vapor lock" is that it is caused by a low
pressure area/combined with hot fuel on the EFI pump intake
which cause the gasoline to flash to vapor - naturally the EFI
pumps can not pump vapor - therefore as fuel is injected from
the high pressure side of the pump (reducing pressure on that
side), vapor can form there as well. In any case,
insufficient fuel is injected into the engine.
Since the injectors are still clicking
open, it would seem that any vapor on that side of the pump
already has a chance to vacate the line (through the
injector) - so my assessment is that it is not the relief of
vapor/gas from the high pressure side that remedies the
problem, it's removing the gas from the low pressure side
(pump inlet) and thereby permitting liquid fuel to be pumped
that "cures" a vapor lock situation.
So I am puzzled why a gas vent on the high
pressure side would have much (if any) effect on vapor lock.
IF there is pressure on the injector side - I question whether
it would be as high as pump pressure - and even if it were,
the injector opening would provide a path for it to be release
- not to mention the pressure regulator. So as I said -I'm a
bit puzzled as to the mechanism that a vent in the high
pressure side prevents vapor lock.
In my opinion, there are two ways to
reduce/eliminate the vapor in the low pressure side - either
cool the fuel sufficiently (somewhat difficult to do) or to
increase the pressure in the low pressure line forcing the
vapor back into the liquid - ergo - use a boost pump.
FWIW
Ed
Sent: Saturday, August 13, 2011 2:53 AM
Subject: [FlyRotary] Re: vapor lock
Hi Ed,
I believe it's simply a return to the tank from the high-pressure
side via a very small orifice. How small I do not know.
Finn
On 8/10/2011 9:28 AM, Ed Anderson wrote:
The one I potential preventive
measure/fix I have not looked into is the vapor
by-pass/dump that I know a few folks are using. I search
the archive but could not find a description of this
method - anyone care to provide one?
|