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>at 22 psi the air would likely occupy even more
space
The opposite is true. Air space reduces substantially when
you increase pressure. Think of coolant as a solid, and air as a giant
spring. When you add btu's to coolant, it immediately responds by expanding.
This causes the air molecules to compress...a lot.
There are some fun exhibits at the science museum I
volunteer at we use to demonstrate air/ water compression. An eye dropper inside
a pop bottle. When you squeeze the pop bottle, the eye dropper plummets to the
bottom. When you let go, dropper rises to surface. The pressure increase when
you squeeze bottle causes air in dropper to compress(less air volume). This
allows water to displace that air....dropper is now heavier and falls to bottom.
It's really ironic. You can design a system that seems to
work fine. You fly with that for years with no failures( well I guess you could
call the pinging and high temps a failure). But a small change can greatly
reduce your risk. There's a lot of value to changing your air bleed design to
one that dynamically removes air. No shrader valve, no repeated cooling cycles
to remove air. By "dynamic" I mean that it automatically removes air from the
system. No muss no fuss.
As you design system, just pretend their is air at the top
of each component. Then find simple way to allow that air to move to higher
component in system. So, my radiator is lowest point in system. If I place my
radiator tube near the top of radiator, then all air naturally leaves rad and
flows to engine. Next I look at highest coolant passage in engine. In my case I
had to drill and tap a little 1/4 npt into the coolant manifold, then run tube
from there up to highest point in system. Suddenly I've got a system that
automatically removes all air immediately. Try as I can, I can no longer trap
air anywhere. If I develop compression leak that pumps air into system, it has
much less effect, because it rises out of the coolant flow. When I drain and
refill, it all immediately and rapidly fills, I can get every drop back into the
system.
Dynamic air bleed is a safety advantage, easy to
accomplish. Each of these safety advantages adds up mathematically.
Likewise, contrary to popular theory, leaving two cups of
air under cap increases safety. You can prove that to yourself with simple
experiment I described earlier.
-al wick
----- Original Message -----
Sent: Friday, October 05, 2007 9:07
AM
Subject: [FlyRotary] Re: Coolant Water
Pressure
Yes, at 22 psi the air would likely occupy even more
space, but since I do my runup with the cap off or loose, there is no pressure
during the process. So while I have never measured it and it probably
varies from one time to the next, there appears to be approx 1/3 of the top
part of each core which has air on the initial fire up of the engine - after a
complete drain and refill of the coolant system.
I must admit that the first several times of draining
and refilling coolant, not being as knowledgeable as I am now, I almost cooked
the engine, because I assumed that when the header tank was full - the engine
had all the coolant it could take. Rapidly climbing coolant temps and
pinging of hot engine cooling off soon make it clear that just because the
header tank was full didn't mean a whole lot. Of course, I noticed after
each run up that the coolant level in the header tank would decrease
permitting me to put more coolant in. That finally made me realize what
the problem was - would have been very nice to have this list around back then
{:>)
After burping the system there is still small amount of
air left, but the overflow tank set gradually removes the remaining air over a
couple of flights. Then the hydraulic "lock" phenomena starts with
initial pressure of 21-22 psi immediately on engine start, dropping off
quickly to zero and then gradually climbing back to 5 - 7 psi as
the coolant heats up.
But, other than having to "clear" the air out with a
couple/three run ups to 5000 rpm, it works just fine and has since 97. I
occasionally toy with the idea of putting in simple small air bleed on the top
of each - but, like I said, it works fine and other things to do
{:>)
Sounds like your approach will avoid my burping
problem. However, Lynn has mentioned that even in the car installation
it often takes burping the engine to get the air out.
Ed
----- Original Message -----
Sent: Friday, October 05, 2007 11:12
AM
Subject: [FlyRotary] Re: Problem?
[FlyRotary] Re: Coolant Water Pressure
Hi Ed,
for sure I saw your installation before (numerous times...), but I do
not recall your exact pluming.
Your description below sounds like inlet and outlet are facing
down.
At 22psi it should even be more like 1/2 the radiator with air :)
Anyway, I assume waterflow is radical enough to strip the air out in 3
trials.
My system will have a bottom inlet and a top outlet. If it doesn't fit
the outlet may exit the bottom of the tank but will have an internal
standpipe - this way there is next to no space where air can get trapped,
just a small bubble atop the standpipe, won't be big enough to cause any
cooling detriment.
I still see BMW motorcycle oil-coolers mounted this way. Don't know the
exact make-up today, but the earliest ones where simple single pass bottom
feed bottom exit (cheapest solution and esthetically least disturbing), a
big problem to purge. 1/4 was useless because of trapped air...
Furthermore, if the pump had a little leak or just a long time between
runs would drain the oil fro mthe cooler and at start-up you had a fresh
load of cold air inthe cooler! As it heats up the air-bubble expands and
reduces cooler volume even more...
Best Regards,
TJ
snipped..
In my case, if I do a complete drain and
refill of the system, on the first run up the core's tanks will be
hot approx 2/3 of the way up and then they are much cooler - indicating
that the remaining 1/3 of my core is filled with air. It generally
takes me 3 runups reaching 5000 rpm before I can touch
the core tanks and find them hot all the way from top to
bottom. So depending on your radiator set up that might be something
you can quickly check.
snipped....
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