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I have the pressure cap right on the engine...no airspace. then if it overflows it goes to a catch can, then sucks it back in when the engine cools. this zero air is the reason for the pressure I'm sure.
Bob Mears
-----Original Message-----
From: Bill Bradburry <bbradburry@bellsouth.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, 25 Feb 2008 10:21 am
Subject: [FlyRotary] Re: Water pressure
Bob, how is your cooling system set up? I was getting high water pressures and blowing out of the overflow when I had a pressure cap on the radiator.
I changed that to a radiator cap that has no pressure containment valve on the radiator, took the overflow hose from the radiator to the bottom of an overflow bottle (a modified fire extinguisher) which has a 23# cap on it. The overflow from this bottle vents to the outside, but so far, has never vented. The bottle is about ¾ full of coolant. This eliminated my high pressures and stopped all the blowing out of the overflow. I think that this is similar to the way most of the cooling systems are set up on the list.
The air in the top of the overflow bottle prevents the hydraulic lock that Ed is talking about below, but ensures that there is no air in the circulating coolant. This didn’t solve all my cooling problems, but it eliminated one of them. :>)
Bill B
Cool deal...thanks guys. I have a 30lb. cap and havent let it get there yet to see if it blows out to the overflow tank. I keep thinking that if I had a regular automotive 15lb. cap it would already be pushing by that and its jsut idleing.
-----Original Message-----
From: Ed Anderson <eanderson@carolina.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, 25 Feb 2008 6:59 am
Subject: [FlyRotary] Re: Water pressure
Bob, if there is no air in your coolant system, you may be observing an hydraulic lock type phenomena. My water pressure will immediately zoom to 21 psi on engine start up. As the engine warms up the pressure drops back down. My understanding is that with no air and the incompressible nature of a liquid - that even small perturbations anywhere in the system can cause the sensor to signal pressure. As the engine warms and a very small amount of expansion in block, rad cores, lines etc. happens that is enough increase in volume of the "containment" for the pressure to lower.
This is why some folks recommend leaving a small amount of air under the cap. If you are not seeing oil in your coolant or bubbles then its unlikely you have a busted O ring.
----- Original Message -----
Sent: Sunday, February 24, 2008 11:52 PM
Subject: [FlyRotary] Water pressure
I ran my 20B at idle, till about 160 degrees. My water pressure rose up to 23 lbs. That seems excessive to me, but I've never watched water pressure before. I've bled the block a couple of times and I dont feel like I have an air lock. Heat is even throughout the radiator. I was a bit worried about compression leaking into the cooling chamber, but I'm not loosing any water, the plugs aren't wet, and it starts flawlessly each time. Hot or cold. Recon I'm all worried about nothing?
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