This was rejected because of
the photo files being too large, so I’ll send one of the pics
separately.
Al
Subject: RE:
[FlyRotary] Re: Coolant Water Pressure
Bill;
Here is the setup
I use. On the first photo, the filler neck is on the left, and connects to
the line going to the inlet side of the pump. The two small lines
(3/16”) coming into the side are air bleed lines going from the high points
of my two radiators (note that the pressure at the filler neck will be near
the lowest in the system.) The ‘overflow’ from the filler cap goes to
the bottom of the accumulator bottle on the right (made from a discarded
fire extinguisher).
The accumulator
bottle overflow goes over board, but coolant only goes out here once on
first heatup. When cold, there is only about 3 – 4” coolant in the
bottom of that bottle, so there is air in there that compresses as things
heat up. Coolant forced out of the filler neck on heat up is draw back
in on cooldown.
The idea is that
whenever the engine is running, there is positive pressure on the system –
at the pump inlet; reducing the chance of pump cavitation at high RPM.
And positive pressure is maintained at altitude even when throttling
back and the coolant temp is decreasing.
Originally I had
a 23# cap on the filler neck, and 15# on the accumulator bottle. I
later reversed the two to lower system pressure on initial heatup (as soon
as the engine heats up at all the pressure goes to filler cap pressure), but
it still gives me the sum of the two caps under any extreme condition to
protect against boiling. Keep in mind that the caps are ‘differential
pressure’ so at altitude the max absolute pressure in the accumulator bottle
is reduced by the reduction in the ambient.
Al
-----Original
Message-----
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry
Sent: Thursday, October
11, 2007 8:49
AM
To: Rotary motors in
aircraft
Subject:
[FlyRotary] Re: Coolant Water Pressure
Lynn, I don’t know what
we would do without you.
I have
several questions.
Where
can I get a good accumulator tank?
I was
thinking of making one out of a used fire extinguisher and was also
looking at one from Moroso that looks like a flat canteen. The one
from Moroso has an inlet on the bottom and one on the top side as well as
one for the pop off of the radiator cap. Due to space constraints, I
will probably try and make one. I need something about 3” diameter and maybe
12” or so long. Will I need the inlet on the top side? If
so, where does it plumb to?
I
suppose I will still need an overflow tank from the pop off of the radiator
cap?
After
talking with Tracy yesterday, I tried
to see if the engine would stabilize temp somewhere below 230* at 2600
rpm. No joy! I suspect that I will need to increase air flow to
get this to happen. I will try an leaf blower on the cowl
today.
My
pressure stabilized at 22 lbs (cap in constant blow off relief) but the temp
would not hold. If I had this same condition with the system you
described, what would prevent the air from blowing off and then water from
the accumulator?
It
seems to me that no matter what system you have, the pressure has to
stabilize below the pressure rating of the radiator cap, else you will be
losing first air, then water????
Bill
B
From:
Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of
Lehanover@aol.com
Sent: Wednesday, October
03, 2007 10:28
AM
To: Rotary motors in
aircraft
Subject:
[FlyRotary] Re: Coolant Water Pressure
In a
message dated 10/3/2007
9:08:53
A.M. Eastern Daylight
Time, bbradburry@bellsouth.net writes:
I
think that I would see air under the radiator cap if I had a compression
gas leak? I never see any air.
To
check a piston engine for head gasket leaks, you would put the cylinder at
TDC and pressurize the cylinder to about 150 lbs with compressed air and
check the radiator for air bubbles…How do you check a
rotary?
I
will check the pressure sender against a mechanical gage.
There is
obviously a heating problem, but I think the pressure is higher than it
should be until just ready to boil. I shut the engine off at 210*,
and at 22+ lbs, the boiling point should be well above
250*??
Thanks for the
suggestions of where to look, guys…
Bill
B
It is
extremely difficult to remove all of the air from a rotary engines cooling
system. It is also extremely important. If air is under the pressure cap in
a static situation, it will remix with other coolant when the engine is at
speed. The coolant moves very quickly through the system. The coolant volume
appears to increase slightly because much of the air is reintroduced into
the water. This coolant then becomes a poor conductor of heat. You need the
anti foaming agent in Antifreeze. Just a bit, perhaps 10%. The system with
the relief cap right on the radiator or filler point, starts to offload
coolant as soon as the engine is started. It is in hydraulic lock, and has a
small volume. The actual boiling point calculated for this coolant makes no
difference at all. The cap opens a bit when the trip pressure is attained,
the pressure drops to 22 PSI or whatever for your cap, and a bit more
heating trips the cap again. It is exactly the same as most
cars.
So,
at first in each heat cycle, there may be no correlation between coolant
temperature, and the actual amount of coolant dumped by the cap. This is
only true closer to a constant operating temperature. And then pressure may
be alarmingly unstable with power changes. The accumulator system makes
pressure rock solid.
Make
the pressure cap into a filler cap, sealing only the top lip of the radiator
or filling port. Connect only a bleed hose and run it to the
bottom of a recovery bottle, and put the pressure relief cap on that bottle.
Keep the bottle about 1/3 full. Note after several heat cycles, the amount
of water you need to add to keep that bottle 1/3 full is reduced each time.
Once all of the air is out of the cooling system, no more coolant need be
added to the bottle.
Heating and
cooling of the system, makes sweeping changes in coolant volume. The air
cushion in the bottle acts as an accumulator (used in thousands of aircraft)
to maintain a constant pressure and coolant supply.
Race
cars use a Rolairtrol or spin bottle in the hose from the top of the engine
to the radiator. Water enters the bottle at about half height on a tangent
and adds a spinning motion. Water leaves through a center hole at the
bottom.
Trapped air pops
to the top of the bottle and that is plumbed to the bottom of the
accumulator as above.
You
used to get the plans for this thing when you buy a Cosworth race engine.
Does Cosworth know something you don't?
Anyway, after
about three heat cycles (operating temperature and back to room temperature)
the coolant system will be solid coolant with all of the air removed. It
will not be hydraulically locked against the cap.
It
will have the relief cap pressure, and will hold that for as long as the
engine is hot.
I
have a Shrader valve installed in my accumulator tank, and before I start
the engine I charge that bottle with compressed air until the cap relieves
at 22 PSI. Now I know it has pressure, and I know it has 22
PSI.
This
was the stock system on all Mazda cars in the 70s. I didn't invent it.
It is
unlikely that you have leaking compression seals, unless there is coolant
blowing out of your makeup tank, or coolant is running out of your exhaust
system after shutdown.
My
recovery bottle is mounted where the passenger foot well would have been.
Even with the bottom of the engine. So long as the hose ID is less than 1/4"
and the hose enters the bottle on the bottom of the coolant supply, it
matters not at all where that bottle is located. There is a money back
guarantee with this system.