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Hi John,
Sorry, John. Thanks for the
vote of confidence. Was working on understanding K&W, duct and heat
exchangers and seeing so many reponses to your inqurey that I figured
you probably didn't need another input.
I tend to agree with the initial advise you
received. If your radiator cap is at the highest
point of your cooling system then I believe that all you need is an
overflow bottle/jug/container. Well -- I also recommend a 21-24 psi
radiator cap. That is all that I use. The overflow catches
any -- well, overflow. Needless to say your overflow bottom must be
vented to the atmosphere. The system on my aircraft is so effective
in removing the air from the cooling system after a couple of flights, no air
remains- in fact, that causes a condition that first caused me to think I had a
engine problem. So I might as well mention it in case anyone else runs into
it.
What apparently happens is as long as there is a
small amount of air trapped in your system then compression of that air
can/will occur. However, once all the air is expelled from the system, you
get to a condition (verified that Tracy Crook also encounter it - don't know of
anyone else reporting it) I call cold fluid Hyraulic lock in that there
apparently is apparently no more air available for compression. So when the
engine and cooling system components cool down, that contraction squeezes the
coolant (and discharges some into the overflow). So what remains in the
engine has no room for any further expansion. Note:
An expansion chamber would probably preclude this phenomona, but at additonal
weight and complexity.
I first noticed that after about 3 flights (during
which that process apparently expells any significant remains air after a refill
of the coolant system) that immediately (within 3 seconds) upon starting
the engine that my coolant pressure would go to 18-20 psi - long before the
coolant heating could possibly have caused it. I ,at first thought, I had
a combustion leak between the rotor chamber and cooling system and was having
the coolant system pressurized by combustion gas (that is one of the symptoms of
a cooling "O" ring failure). However, there was no loss of fluid, no
indications of combustible in coolant (frequently will see what looks like
thin oily sluge on top of the coolant) and once airborne (or the engine
heated up) the pressure would drop back to a nominal 4-9 psi (depending on
power setting and OAT - note: I do no use a thermostat).
Tracy confirmed the same condition (and we have
different cooling system, his in parallel, mine in series, his with 5/8" lines
me with 1" lines, etc.). I believe that what we are seeing was
the cooling pressure sensor diaphram being pressurized by the kinetic energy in
the cold coolant flow perturbed by the water pump and coolant flow. Since
without any air in the system and the fuild occuping all the space, any small
pressure pertubation is no longer absorbed by the "shock absorber" of a bit of
air in the system and it shows up immediately on the pressure
sensor. Once the engine heats up then apparently there is enough expansion
in components through out the system that the pressure drops back down. Since we
are basically talking about a liquid, as you know very, very little
compressibility occurs.
Don't really know if that is the reason - perhaps
some hydraulic fluid experts could offer further comment.
my $ 0.02 worth
Ed
----- Original Message -----
Sent: Friday, December 05, 2003 11:10
AM
Subject: [FlyRotary] Re: Expansion
Chambers
> Calling Ed Anderson:
> Ed, It's not that I disrespect others,
but I've come to respect you're
> opinions on matters rotary. See what you
get for all you're hard work!
> I recently posted a question about the
need for an overflow bottle and
> expansion chamber and how they should be
plumbed. I was kinda hoping to get
> you're opinion.
>
Regards,
> John Slade
>
>
> >>
Homepage: http://www.flyrotary.com/
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