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.