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Message
Hi Guys,
A timely word of caution. Just want to chuck
in some more addled thoughts on AIR Locks vs VAPOUR Locks. As I mentioned
in another post, It is almost impossible to get a VAPOUR lock in the
pressurised part of an EFI system (unless you are REALLY silly and run the
supply line 1/2" from your exhaust pipe). Lynn Hanover in his post
confirms my notion that vapour locks normally only occur in the LOW
pressure part of the system, especially when a lift pump is used to "suck" fuel
(and therefore subject it to a partial vacuum), especially when they are
close to a heat source and are not adequately shield/insulated.
A properly designed EFI system should have no
problem priming the high pressure EFI pump, because it should ALWAYS have
a head of fuel on it. Either being the lowest point in the system,
or at the bottom of a "Surge", 'Header", or "Make-Up" tank (whatever
you want to call it). However, AIR locks are a different
matter. The fuel system must be designed to allow it to purge any air
entrained in the system, either from initial installation, but
most especially if you happen to run the tank dry, either on
purpose, or inadvertently during flight.
Case in point - I mentioned that I had experienced
AIR lock in EFI systems before. On one occasion, I wasted several
hours and a couple of hundred dollars of dyno time before the penny
dropped. Had I walked away for a few minutes, sat down and thought
about it carefully, the CAUSE of the problem would have been
obvious. But I was too close to the problem, and also
too baffled by my own "BS & Brilliance"(};>) as well ( no smart
comments please ...)
It took somebody else, not associated with
this particular car (it even had the dyno operator flummoxed - and Rocky is
one seriously sharp rotary dude) to ask the right questions,
eliminate all the "red herrings", and come up with the correct answer
- which was that there was an air lock between the two fuel rails.
Fortunately, after a couple of fruitless
hours, Rocky & I eventually agreed that we needed help (yeah I know
what you are thinking ... again, no smart, comments please ...), so
we called in our friendly Motec dealer. He lobs over, looks at the
installation, asks a few pointed questions, and sees the problem
almost immediately. Both Rocky & I ended up with very sore and
very flat foreheads that night - (You know how you slap your forehead when
someone points out the blatently obvious??) - not to mention very sheepish
and embarrassed looks on out faces.
See, the symptom was one rail (front
rotor) was running lean. The fuel system was set up with a 4 barrel
TB and to treat each rotor separately with its own fuel rail, instead
of using the normal primary/secondary injector fuel rail set-up. With the
front rotor running lean, the motor obviously wouldn't make any
power.
It turned out that the bridging supply line between
the two fuel rails was high on the inner guard, and had been put there as
a temporary measure at the race track when an alloy rotary water pump had
to be changed to an earlier cast iron pump, and which fouled on the
existing fuel rail and supply line. Being the highest point in the
system, it naturally trapped a sizeable air lock, which, due
to a combination of circumstances, could not be purged.
The air lock prevent most, but not ALL of the
fuel flowing to the front two injectors. the fact that the hose was a -8
made it all the more difficult to purge. Simply by re-routing the
hose DOWN instead of up, the air lock cleared, and we got back full
power immediately..
Forever the "Doubting Thomas", and to make
sure we had indeed correctly diagnosed the problem, and to
demonstrate the cause, I then spliced in a bleed nipple fitting
in the -8 hose at the top of the loop, re-fitted the fuel line back
up over the strut tower (complete with massive air embolism) where
it had previously been, and the power problem magically
re-appeared. We then bled out the air lock via the nipple, and
bingo, the power came back. So simple, yet it escaped two
really experienced rotary mechanics that night. AgHCF (All gods Have Clay
Feet).
So I just want to exhort you guys to be careful
with your diagnosis of any problems that arise. Think carefully about
it, don't jump to conclusions, ask the right questions, and be
prepared to consult others (which is what this list is about),
Often, we can become too close to a problem and it requires a disinterested
party to be able to see clearly the whole situation. Then try to design
tests to prove any assertions wrong - not right (which is why I fitted the bleed
nipple in the line).
See, I just didn't want to really believe
that an air lock was actually the problem - I didn't even KNOW for sure
that there WAS an airlock in the hose, even though common sense told me
there was. I had to see it to believe it (the "Doubting Thomas" Syndrome
with which I am so heavily infected) - sure enough, on opening the bleed
nipple, there was a rush of air before the fuel began to squirt
out. QED.
The problem was reproducible as well. (As Einstein once said about insanity (with which I am also
infected): "doing the same thing over and over again and expecting
different results").
Cheers,
Leon
----- Original Message -----
Sent: Sunday, June 12, 2005 4:39 PM
Subject: [FlyRotary] Re: Is common sense
dead (rant mode on)
Everyone here is interested in solutions,
SPECIFIC solutions.
Specifically, Follow this general principal:
When you have a theory, find way to prove it's true. Use facts.
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