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Date: Wed, 31 Aug 2011 11:47:32 -0400
From:  <echristley@nc.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: CG Products Intake Manifold
Cc: Dave <david.staten@gmail.com>
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---- Dave <david.staten@gmail.com> wrote:=20
> HOWEVER..... if there is not a method to bleed down the rail the risk of=
=20
> vapor lock exists, as the rail heats, the fuel boils, and the vapor gets=
=20
> trapped in the line.
>=20

<rant mode on>

Vapor lock.  Vapor lock.  Vapor lock!
If you don't eat your peas the vapor lock boogey-man will eat your feet!

</rant mode off>

Could we please put this vapor lock boogey-man myth to rest.  Vapor lock is=
 NOT "some vapor in the line".  Vapor lock, as Al says, is vapor at the pum=
p inlet which destroys the pumps ability to pump.  Vapor lock is dangerous,=
 because the only way to recover from the vapor is to add pressure, and the=
 only thing that is able to add pressure is blocked from doing so by the va=
por.  If there is some vapor AFTER the pump, it will quickly disappear once=
 35 to 50 psi bears down on it and it gets pushed through the injectors.  I=
n the worst case, there would be an imperceptible hick-up as a lower densit=
y volume of fuel is spit out of the injector at some point.  You are MUCH m=
ore likely to suffer from vapor lock due to bringing that hot fuel back to =
the vicinity of the pump, than from just leaving it forward of the firewall=
.

The amount of angst from inconsequential matters in this thread is starting=
 to get comical.  First, there is hand-wringing about restricting the fuel =
flow.  Really?  Through a -6 line?  Is there anyone on this list that is ab=
le to flow more than 20gph for any length of time without melting their eng=
ine?  Try this experiment.  Put a -6 line as an exit out of a gallon jug.  =
Fill it with water and time how long it takes to empty.  Anything less than=
 3 minutes indicates that a -6 line would suffice for the maximum sustained=
 flow that will be needed in real life with nothing more than gravity feed.=
  Add as many angles and banjos if you think that'll make a difference.  No=
w, seal the container and pressurize it to 35psi.  Try not to hurt the neig=
hbor's kids with your new SuperSoaker.  You'll want to trade down to a smal=
ler size exit line so that you can actually get in a little play time befor=
e the tank runs dry.  Seriously, with a -6 line you can add every kind of t=
wist and turn you could imagine and still have multiple overkill amounts of=
 flow.  If that doesn't convince you, measure the size of the injector's bl=
ow hole.  Multiply that area by the number of injectors you're using.  Calc=
ulate the total exit area, then calculate how many multiples of that go int=
o the area of a -6 line.  Now consider that the injector's blow hole has a =
pintle as an additional restriction. My six cylinder Dakota, rated for 210H=
p, has a fuel rail that looks to be about 1/4".  Would Dodge be dumb enough=
 to kill the performance of the engine by cheaping out on sizing the fuel l=
ine properly?  (Don't answer that.  I'm afraid of the answer.)

At the same time, you're worried about the fuel getting hot.  With that muc=
h fuel flowing, if heat is being transferred to it that quickly, you either=
 have the lines routed through your exhaust stack ... or ... hell, exactly =
how WOULD you get the fuel to heat that quickly?  And you would you heat it=
 that quickly without melting the hose?  BTW, raising the temp of the fuel =
is useful.  Makes it vaporize better.  Even with the extremely low flow rat=
e I had, I still got condensation on the intake manifold when it was nearly=
 100* outside, and I know that the fuel was at least 85*.

As for pressurized lines.  50psi is not "high pressure" for an aluminum or =
quality hose fuel line.  You carry that much pressure in your tires, and lo=
ok at how everyone treats them.  It's not until you get to some significant=
 fraction of thousands of PSI that you start to need connections more exoti=
c than hose clamps.  Fuel systems in thousands of the cheapest cars rolling=
 down the highway prove it every day.  Of all the leaks I had in my fuel sy=
stem, NONE of them were in the high pressure section.

My fuel comes out of the tank, through a large filter to the pumps.  The re=
gulator comes next, with an upset in the seal to allow pressure to bleed of=
f after shutdown. The pressure wasn't a problem. Some mysterious vapor lock=
 demon wasn't a problem. Having pressure hanging on for days, slowly pushin=
g fuel past the injectors to pool in the closed intake manifold, was a seri=
ous safety concern.  A single line from the regulator carries fuel through =
a small filter (in case a pump sheds parts) up to the firewall.  A vertical=
 section insures that any fuel that is boiled from engine heat after shutdo=
wn stays forward of the firewall.  FWF, a hose carries the fuel to the prim=
ary injectors that are located in the stock location using the stock rail, =
where it passes through a banjo joint.  Another stock banjo joint carries f=
uel to the secondaries using the stock rail and another banjo joint.  I jus=
t 50psi, silicone fuel hose and hose clamps.  With 460cc injectors, I got e=
nough fuel through to repeatedly flood the engine.