|
|
Lynn explains perfectly the clear advantage of using a pressurized expansion
tank - NOT use the unpressurized "overflow/expansion" tank.
Bill Eslick agrees. I agree.
- It is interesting that Lynn, whose experience goes back a long way,
calls the pressurized system the "Mazda system" (i.e., the way they used to
do it) and the unpressurized system the "auto system" (the way most still do
it - but not all).
Now, it should be noted by anyone planning to install a cooling system - or
interested in refining and improving their existing system - that, as
mentioned in previous e-mails maybe last Summer, the late Nineties Ford
Taurus's use the "pressurized system" - no sucking liquid back into the
radiator. Pressure cap is right on the translucent plastic expansion tank.
It has a tube running out the bottom to the bottom of radiator so fills from
bottom up and thus purges air (not quite same as 2 evap cores in our
planes). It appears to me to be IDENTICAL to what Lynn is describing - and
it is modern, and it should be available in auto salvage yards.
- All the water in-out tubes and air in-out tubes are SUBMERGED under
liquid coolant in the pressurized tank.
- A big deal is that you not only have an air bleed from top of
radiators (corners, cross-over hoses or whatever) BUT ALSO from the high
point in the engine block.
-- It hasn't been discussed but I believe those "air bleeds" should
be relatively small tubes for similar reason that we put "flow restrictors"
in mechanical oil pressure lines - if the line breaks, you don't dump all
your oil instantly. Now, in the case of the coolant sys we are talking
about, I'm not particularly concerned about the line(s) "breaking" as I am
concerned about having an alternate flow path for coolant to have an
alternate path after the 1st of 2 evap cores and before the 2nd core, to
simply "bleed by" the 2nd core and go straight to the water pump inlet
without being cooled. Same rationale for the small "air bleed tube" from
top of engine block water passages - that is relatively higher pressure and
thus there will probably be a continuous flow from that point in the engine
block directly back into the relatively lower pressure "pressurized
expansion tank" (which will be about the pressure of the pump inlet since
that is where the tank is plumbed to), thus bypassing the rest of the engine
cooling galleys.
I suppose if I were to say, "This is the way it should be." I'd probably
provoke something like "primer wars", etc where there are more than one way
to skin a cat.
- I simply think a "pressurized expansion tank" system, properly
implemented as discussed above, is a clear "winner" over the old
"unpressurized burp tank/suck it back after engine shutdown tank system".
David Carter
----- Original Message -----
From: <Lehanover@aol.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, December 06, 2003 10:36 AM
Subject: [FlyRotary] Re: Expansion Chambers
<snip>
With the pressure cap in the system between the radiator and the recovery
bottle, any coolant that gets by the cap and into the bottle cannot be
recovered
until the engine has cooled to ambient, or close to it. Only then will the
system pressure drop below ambient and coolant in the bottle will be at
ambient,
and thus at a higher pressure, so it replaces the coolant lost by the
system..
Not all of it, but close, because it takes some pressure to open the return
valve in the cap. The make up bottle has a level marked on it so you can
fill
with coolant to that point. Notice also there are marks for cold and hot
coolant. About a quart apart on the bottle. This is so there is no chance
that a
system cooling down will ingest air from an empty recovery bottle.
The water pump is mounted very high on the engine, and a big dose of air
will prevent the pump from circulating coolant, with tragic result. Notice
that
in the "car" system, that coolant is full into the cap well on the radiator.
When the system heats up, it is in hydraulic lock and builds pressure up to
the
relief setting on the cap. Only then does the cap begin to bleed off coolant
to maintain the rated pressure. The cap well on the radiator is not the very
best way to remove air from a rotary engine. If you take the time to run
through
several heat cycles after you have the system open, then you will get most
of
it out.
The early Rotary powered cars had a plastic bottle on the firewall, and that
bottle had the pressure cap on it. There was a cap on the radiator used for
filling it but had no pressure element. Mazda was not alone in this
practice..
The advantage here was that the engine didn't have to cool all the way down
to
recover coolant from the recovery bottle. Small volume changes from changes
in
heat load would cause fluid exchange from the pressurized bottle to the top
of
the radiator. Coolant entered the bottle from the bottom, so a slug of air
forced out of the radiator would pop to the top of the recovery bottle and
when
power (and heat) was reduced in the engine it would recover only water from
the bottle.
This, because the pressure in the bottle would be (for a few seconds) higher
than the coolant system pressure. I keep my pressure bottle about 1/2 full.
I
have added a Shrader valve so I can pressurize the system before I start the
engine. Both systems work well, and most people use the "car" system.
Because
they are not aware that there is a (in my mind) a better system. And there
is
little to fear from using the car system.
The advantages of the old Mazda system are: it will return all of the
coolant
in the bottle to the engine in case of a leak. You get nothing back from the
"car" system until the plane is on the ground and cold. This system is much
better at removing air from an operating system. The weights are about the
same
for both. You can still find them in the junk yards but you can make one if
you want. You can mount either system anywhere. They don't need to be higher
than anything to work. The car system is just a little less well off when
mounted
low but not a problem, but it is open to ambient. The Mazda bottle can be
mounted anywhere so long as it is upright. And "anywhere" can be a real
handy
location.
Lynn E. Hanover
|
|