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.