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.