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Charlie and Jeff,
If I am seeing things correctly, Charlie's connections to the expansion tank are both near the bottom of the tank due to the dip tube attached at 10 o-clock. This is essentially how I have my expansion tank connected. I installed a Schrader valve at the
top of the thermostat housing which is the highest point in the cooling system. My entire expansion tank is below the level of the thermostat housing. When filling the system, I add coolant to the expansion tank and pressurize it through the overflow port
in the filler neck while opening the Schrader valve. When coolant is expelled from the Schrader valve, the system is purged of air. A filler cap at the highest point is not needed.
The expansion tank does not back-fill with coolant unless the filler cap is released and also the Schrader valve is opened. Both conditions are necessary for the expansion tank to back-fill.
Having both the inlet and outlet lines connected below the surface of the expansion tank is a good thing in my opinion. They just need to be separated by enough distance that any bubbles can separate upward rather than be drawn into the outlet line. I
keep the inlet line to the expansion tank restricted for two reasons. One is that coolant circulating through the expansion tank is bypassing the radiator and not contributing much to cooling. The other is to limit the pressure seen in the expansion tank.
With a thermostat in the system that is not fully opened, I see pressures in the thermostat housing on the water pump side of the thermostat of up to 40 psi at high RPM.
With my system, I need at least a quart of air space in the top of the expansion tank when cold. If the air volume is less than this, the expansion of the coolant will fill the entire system with liquid when hot. If there is residual air space in the expansion
tank, the pressure in it will vary continuously with operating temperature. If the system becomes completely filled with liquid, the pressure is constant at the relief pressure of the filler cap.
That is how my system behaves, for what it is worth.
Steve Boese
RV6A, 1986 13B NA, RD1A, EC2
From: Rotary motors in aircraft <flyrotary@lancaironline.net> on behalf of Jeff Whaley <flyrotary@lancaironline.net>
Sent: Thursday, January 29, 2015 8:05 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: swirl / expansion tank configuration
Charlie, I don’t think your system will work as you expect and I’m pretty sure it is not the same as the Hanover-Setup. Attached is the Hanover cooling system diagram … note all the cooling elements (radiator, hoses, filler bottle) are
completely full of glycol (green); only the expansion tank (approx 1 litre, with stant lever cap) has room for air, filled only about 1/3. The location of the expansion tank is shown higher than everything else in the diagram but can actually be located lower;
what is important is the connections be as shown, i.e., highest point of saturated cooling system connects to bottom of expansion tank, expansion tank is only 1/3 full and this is where you install the pressure cap.
The location of your steam lines to top of expansion tank is correct but I think with your bottom connection going to pump inlet what will happens is any portion of the expansion tank lower than highest point in the system will simply back-fill
with coolant and you will no longer have an expansion tank but rather a coolant tank. I believe your methodology will work if at least 1/3 of expansion tank is the highest point in the system. One thing for sure is with the pressure sensor located on the
pump inlet side, you will be measuring the lowest pressure in the system.
Jeff
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From:
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Charlie England <flyrotary@lancaironline.net>
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Subject:
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swirl / expansion tank configuration
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Date:
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Wed, 28 Jan 2015 17:57:34 -0600
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To:
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flyrotary <flyrotary@lancaironline.net>
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I'm setting up the cooling plumbing for the Renesis (RV-7) & wanted to try the setup used in a lot of current autos, where the 'steam' lines go to the expansion tank and the coolant
in the expansion tank is constantly pulled back into the input to the water pump. I'm hoping that this will do a continuous purge, similar to Lynn Hanover's setup with the extra swirl tank. I couldn't get the swirl/expansion tank higher than the water pump
outlet (highest point of the system), so I modified the hotrod expansion tank shown, with the hope that when the system cools, it will be forced to pull only coolant back into the 'steam' lines. The plan is to collect the steam lines from the radiator, flywheel
end iron, and pump outlet & return them to the port located at the 10 o'clock position on the tank.
I'm assuming that I'll need to add a fill port on the pump outlet (top of engine) and fill from there after partially filling & capping the expansion tank. Any thoughts/criticisms?
Charlie
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