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| Take a look at the Holley HP series pumps. They look to be about the same length as the Walbro, but the inlet and outlet come in the sides instead of the ends, effectively making the install more compact. Also, they are a gerotor type pump, so should be quieter and more robust. They're also twice the price of the Walbro.
Mark S. On Sun, Sep 4, 2011 at 3:46 PM, <CozyGirrrl@aol.com> wrote:
We currently have a pair of new Walbro GSL393 EFI pumps, is there something
comparable that is not so long?
Chrissi &
Randi
www.CozyGirrrl.com
CG
Products, Custom Aircraft Hardware
Chairwomen, Sun-N-Fun Engine Workshop
On a low
wing plane (at least the RV's), it will usually be impossible to gravity-feed
all fuel to a sump tank, since the lowest point on the a/c will likely be only
an inch or so below the low point in the tank. (I never said 'pump to a pump';
was that a typo?) While Ed A's vacuum-fed sump is obviously successful, I
can't get comfortable with using that technique unless I exactly duplicate
everything in his system. My personal preference is to keep as much of the
fuel system as possible out of the engine compartment, to minimize heating of
the fuel until it will actually be going through the injectors.
I think
you make my point on life risk vs design decisions. Life risk should obviously
carry more weight, but if it's the only criteria, we'd find a way to never
leave home. Van could have found a way to pull fuel directly from the bottom
skin of his tanks, and feed it directly to the carb with the lines &
shutoff valve hanging under the fuselage, and there might be a slight
reduction in 'life risk'. But the system he chose has had zero problems in
unmodified installations, meaning to me that the choice to keep the design
cleaner was justifiable. Furthermore, difficulty in maintenance can actually
*drive up* life risk. I consider it safer to make everything except a single
mechanical joint (fuel pickup to bulkhead fitting) the only thing that I can't
conveniently inspect.
I tried to keep my primary fuel delivery path to
the pump(s) as close as possible to the 'stock' configuration from the
designer. At least in my feeble mind, this is the best I can do to minimize
life risk, since it's been successful in at least 7,000 flying a/c.
Are
we closer to being on the same page?
Charlie
On 09/04/2011
11:34 AM, Al Wick wrote:
Charlie wrote:
<If you must pump to the sump, then the vent can't 'go anywhere'
unless you're willing to risk pumping fuel overboard
Yeah. It seems so. It's a bit strange to think someone MUST pump
to the pump. I'd be quick to question that assumption.
< removing several dozen screws, the vent line and fuel line,
and then removing the tank before I could remove the 6 or 8 screws that
<hold on the access plate to the tank
So, once every twenty years you might have to
access the pump. And the number of screws is your reason to have higher
risk fuel design? I try my best not to let anything get in the way of
improving safety. That's why I changed my fuel design even though I'd never
had a problem. I want that extra safety margin from sump tank with two wet
pumps, self cleaning filter. It's real. It's significant.
<we would choose maintenance ease vs life risk: you have to be
honest; *every* decision makes that choice
Of course not. I'd never agree with a sweeping
assumption like that. Life risk SHOULD always carry more weight in a
decision.
-al wick
----- Original Message -----
Sent: Friday, September 02, 2011
12:21 PM
Subject: [FlyRotary] Re: vapor
lock
I'd have to differ on a couple of points.
If you
must pump to the sump, then the vent can't 'go anywhere' unless you're
willing to risk pumping fuel overboard.
On a typical RV, it would
require removing several dozen screws, the vent line and fuel line, and
then removing the tank before I could remove the 6 or 8 screws that hold
on the access plate to the tank. So, there is a bit of a maintenance issue
for us. If not for that, I'd use in-tank pumps. For my application, the
external sump would add more weight/complexity.
To the implication
that we would choose maintenance ease vs life risk: you have to be honest;
*every* decision makes that choice. The safest G/a factory plane in the
world uses bolt-on wings instead of a one-piece wing; a one-piece would be
both lighter and safer.
Charlie
On 09/02/2011 01:04
PM, Al Wick wrote:
What fine work Steve. I love it when
someone converts theory to facts. You measured that all at sea level.
Now just subtract 5.35 from all your pressure numbers if you fly at 12k
ft. You've now measured all of the variables that affect vapor lock.
Only remaining item is measuring pressure at your pump inlet. You then
can predict exactly how safe your plane is without ever flying! How cool
is that?
I use a submerged fuel pump for added
safety. Two actually. Easy to maintain, just remove the 6 screws that
hold the pumps in place. So there is zero significance to the argument
of maintenance. Can't imagine how anyone could claim maintenance is more
important than life risk anyway. I return all fuel to my 3 gallon sump.
Vent can go anywhere, you don't have to tie vent into main fuel vents.
Once again, nice work Steve.
-al wick
----- Original Message -----
Sent: Friday, September 02, 2011
12:04 AM
Subject: [FlyRotary] vapor
lock
For those concerned about the formation of vapor in a
pressurized fuel rail, I've attached a plot of data collected from
local samples of 100 LL avgas, 87 octane auto fuel with no ethanol, 91
octane auto fuel with 10% ethanol, and tap water. The water was
measured just as a check on the method.
The data would be considered more of a true vapor
pressure rather than a Reid vapor pressure due to the method
used.
The data indicates to me that if the fuel pressure in
the fuel rail is 35 psi as measured with a regular gauge referenced to
the atmosphere at sea level, the temperature of 100 LL or 91
octane 10% ethanol in the rail would have to be in the
neighborhood of 240 deg F for it to form bubbles of vapor
(boil). The sample of 87 octane would require a temperature
of about 215 deg F to form a vapor phase.
My take on this is it may be more productive to be
concerned about the fuel supply to the high pressure pumps rather than
worrying about "vapor lock" downstream of those pumps.
This seems to be the conclusion reached by the recent thread on this
subject, possibly now supported by actual data. Of course the
data only applies to the samples I obtained.
The higher temperature tolerance of the auto fuel with
ethanol compared to the auto fuel without ethanol was surprising to
me.
But I only collect data --- it is up to an engineer to
make sense of it ;>)
Steve Boese
RV6A, 1986 13B NA, RD1A,
EC2
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