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.