From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Lehanover@aol.com
Sent: Wednesday, October 09, 2013 9:00 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: : Multiple coolant pressure Caps

On the two cap situation: I would make the lowest cap on the radiator impossible to open. Perhaps a 28 pound racing cap. The upper cap on an accumulator should control pressure release. Perhaps a 22 pound

Stant Lever cap. In the picture is a layout that I have used. I did not invent this system. Except for the swirl pot, it is the stock system from early RX-2s,3s and RX-4s. The book that comes with each new Cosworth engine show a short aluminum swirl pot right outside the engine before the radiator. So, I added that to my system. It is a simple accumulator as used in large aircraft and complex hydraulic systems all over the world.

This system will supply a small amount of coolant in the event of a leak.

It maintains a constant pressure with no coolant leaving the system as in big American cars up through the 80s. In the double valve pressure caps, coolant lost on warm up is pushed into a recovery bottle and saved. It cannot return to the system until the engine is nearly cold and the coolant pressure drops below ambient. This system removes air bubbles and foam from a rotary in three heat cycles. You check the accumulator after each heat cycle and discover  it is no longer 1/2 full.

On about the 4th heat cycle, no additional coolant need be added. You have removed air and need to replace that volume with coolant.

The pressure control is done by the cap on the accumulator bottle. The pressure cap may indeed open to maintain the correct (Cracking) pressure. Note that the cap venting to reduce pressure only lets air escape, not coolant. In racing we are required to have all of this end up in a bottle or catch tank of at least one quart capacity. In aircraft use that hose might come up in the wind screen a few inches onto the passenger side. If you wife starts screaming like she does on occasion, or the passenger asks about the green stuff, be assured there is a problem that needs to be addressed on the ground within a very few minutes. This means that system pressure has overcome the pressure cap and filled the accumulator against cap cracking pressure. A badly overheated engine and, or, a failed seal. I have lost only one engine since 1980 to coolant loss. When a Chinese "Cresent" wrench was dropped in front of my car by a Corvette, bounced once and went all the way through my radiator. My driver heard the noise above the engine noise but failed to note the temperature change. So, not counting the wrench, I have suffered no coolant related failures with this system. The car ran about 7 laps with no coolant at all in it.

I raced a Fiat for 5 years before that with this same system and no failures.

Note that the accumulator need not be located at the highest part of the system. Mine is on the floor of the car (where the floor would be if there was one). My catch tank is right beside the accumulator and is filled from the bottom.

There are aluminum versions of the accumulators that are designed to work with American caps. They work just fine. I used the RX-2 bottle because I had a good one.  I installed a Shrader valve to my bottle and charge the system to cracking pressure before starting the engine. Just to be sure everything is working properly.

Lynn E. Hanover

Bill:

I've never seen such a radiator cap; are they common or custom?

I'll look to see if one is available.  I was also thinking about the overflow port and feeding it into my expansion tank - thanks, I'll seriously consider that as well.

Jeff

 

Jeff,

On my radiator, I have a solid cap, no pressure relief. This cap seals at the top of the radiator neck, not down at the bottom where the pressure cap seals. That allows the coolant to rise into the overflow neck. The overflow neck nipple is then plumbed to the bottom of my swirl can and the swirl can has a pressure relief cap on it. I think 21 lbs on the pressure relief cap.

This system automatically eliminates air and I periodically check the swirl can to see if I need to add coolant. I only have to add coolant if I have had the system apart for maintenance and introduce air.

Bill B

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