Cooling, Pressure, and Caps

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Cooling, Pressure, and Caps

Postby lazyuniondriver » Fri Oct 26, 2012 7:38 pm

For any of you guys wondering what pressurized cooling systems are all about, how and why pressurized radiator caps work, plus other cooling system tidbits as well as coolant recovery, here is an illustrated webpage you may want to skim over.

http://www.barsleaks.net/faq.html#How%20Does%20The%20Radiator%20Pressure%20Cap%20Work

For some reason, I've found lots of pressure caps sealing zero pressure systems. The early cooling systems were never designed as pressure vessels, so any pressure they contain is not meant to be there and can only cause stress at gasket mating surfaces.

You can retrofit a pressure cap in a second by clipping the brass vacuum valve stem in the center bottom seal with a pair of side cutters opening up the hole between the lower seal and the top seal which allows the cap to continuously vent to the overflow tube. Depending on the brand of cap, the vacuum spring and stem piece may remain trapped inside. If the pieces would ever work themselves out of the cap, I don't think it would be an issue. Or if you prefer, an OEM style cap may be obtained at additional cost.
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Re: Cooling, Pressure, and Caps

Postby Boss Hog » Fri Oct 26, 2012 7:45 pm

later models ran about a 4 pound pressure cap with basically the same system
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Re: Cooling, Pressure, and Caps

Postby lazyuniondriver » Fri Oct 26, 2012 8:14 pm

Boss Hog wrote:later models ran about a 4 pound pressure cap


Here's the skinny on the 4 pound cap, even the boiling temp at 4psi.
This link perhaps more informative than the previous.
http://installer.aed-inc.com:8191/Stant%20Technical%20Info/TempTalkRadCap_4.htm
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Re: Cooling, Pressure, and Caps

Postby Boss Hog » Fri Oct 26, 2012 8:34 pm

I just stated a fact , I am sure some are interested in your findings. you could run it without a cap at all

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Re: Cooling, Pressure, and Caps

Postby tmays » Fri Oct 26, 2012 8:38 pm

I've run them with a pressure cap, with a non-pressure cap, and with no cap at all. Personally I could detect no difference other than some coolant sloshing out with no cap while going downhill over rough ground
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Re: Cooling, Pressure, and Caps

Postby challenger » Sat Oct 27, 2012 6:28 am

Why subject your thermosyphon cooling system to internal pressure when the advantages are neglible? What you will be doing is subjecting your cooling system to internal pressure, which will unnecessarily stress gaskets and radiator core and increase the likelihood of troublesome coolant leaks.
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Re: Cooling, Pressure, and Caps

Postby Jim Becker » Sat Oct 27, 2012 9:35 am

challenger wrote:Why subject your thermosyphon cooling system to internal pressure when the advantages are neglible?

The same reason you pressurize any other cooling system. It allows higher temperatures and thus higher cooling capacity. For pressures around atmospheric, each pond of pressure adds about 3 degrees to the boiling point of water. For the original power output and typical use of a Cub, it wasn't needed. As more tractors were used with rotary mowers (increased power used and more prone to radiator plugging) adding a pressure cap was a reasonable way to up the cooling capacity.

Our members on the Colorado eastern slope need a 3 pound cap just to maintain the same boiling pount of those of us near sea level.
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Re: Cooling, Pressure, and Caps

Postby lazyuniondriver » Sat Oct 27, 2012 11:27 am

I think at one time everyone has witnessed someone removing a radiator cap from an engine that is overheated or has coolant flowing from the drain tube.

As the radiator cap is uncorked, a sudden blast of steam and coolant violently erupts from the neck of the radiator with tremendous force.

This is the best demonstration of how a pressurized system prevents water from boiling within above 212 degrees a sea level. The system when cracked open instantly drops to zero pressure exposing the coolant inside previously heated above 212 to change from a liquid to a gas state, forcefully erupting into a full boil and will continue to boil until the temperature of the coolant recedes to below the boiling point.

Cracking the cap slowly is ineffective in preventing an eruption as eventually the pressure drops below the coolant boiling point when the action starts.
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Re: Cooling, Pressure, and Caps

Postby lazyuniondriver » Sat Oct 27, 2012 10:14 pm

Since we know the boiling point of water can be raised a few degrees for every pound applied to it, shouldn't the opposite be true as well?

I was amazed to watch a refrigeration shop teacher live up to his claim of being able to boil water at room temperature.

He had a Mason jar lid fitted with a Schrader valve which after filling the jar halfway with water, hooked up an AC evacuation pump to it. In less than a minute it was "boiling away". I'm still not convinced it was actually boiling, the definition of boil is heat to bubbling. I didn't see any heating going on, only a whole lot of bubbling so maybe it was just removing the o2 from the water and not actually boiling it.

Anyway, if you've never seen it happen it is something to talk about. Here is a YouTube link to it.

https://www.youtube.com/watch?v=jn1X_I8 ... ata_player
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Re: Cooling, Pressure, and Caps

Postby Jim Becker » Sat Oct 27, 2012 10:46 pm

lazyuniondriver wrote:Since we know the boiling point of water can be raised a few degrees for every pound applied to it, shouldn't the opposite be true as well?

Sure is, about the same rate of change going the other way. Thus my comment about the mile high guys needing 3 pounds just to maintain something around 212. The Wikipedia article on "boiling point" starts off with a pretty good definition.
The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

A liquid in a vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high-pressure has a higher boiling point than when that liquid is at atmospheric pressure. In other words, the boiling point of a liquid varies depending upon the surrounding environmental pressure.

I liked the youtube video. It pretty well illustrates the behavior.
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Re: Cooling, Pressure, and Caps

Postby lazyuniondriver » Sun Oct 28, 2012 9:25 am

Jim Becker wrote:The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.


This is a much better definition than my previously supplied dictionary response.

We know it has to work this way or the principle of refrigeration wouldn't. I have used the same results we witnessed in the YouTube video to my advantage, quickly force feeding refrigerant gas into a system without the compressor turning using only atmospheric pressure and hot water.

Boiling water at room temperature would be easier to explain if we measured both pressure and vacuum readings on the same scale, conversion wouldn't require a chart, only simple arithmetic.

Vacuum "pressure" conversion chart: http://www.engineeringtoolbox.com/vacuu ... d_460.html

For you folks interested, here is another visual aid, "How Pressure Changes Boiling Temperatures" followed by a short interactive quiz after the presentation: http://www.wisc-online.com/objects/View ... ID=ELE2107
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Re: Cooling, Pressure, and Caps

Postby Jim Becker » Sun Oct 28, 2012 9:43 am

lazyuniondriver wrote:Boiling water at room temperature would be easier to explain if we measured both pressure and vacuum readings on the same scale, conversion wouldn't require a chart, only simple arithmetic.

Definitely. A lot of the confusion is probably rooted in the fact that we tend to use atmospheric temperature as "zero", compounded by the fact that atmospheric pressure isn't a constant. Temperature readings are also confounded by the arbitrary choices of "zero" that we commonly work with.
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Re: Cooling, Pressure, and Caps

Postby Bus Driver » Sun Oct 28, 2012 2:02 pm

Way off topic, but the ability to change the boiling point of water by changing the pressure is quite useful. The lumber industry sometimes uses RF drying, microwaves. The water in the wood is thus quickly boiled off. But lumber subjected to more than about 180 degrees suffers loss of strength. So the lumber is in a vacuum chamber and the vacuum is such that water boils at about 151 degrees. The RF ( microwaves) boil off the water and the vacuum removes the steam. Standing trees can be converted to dried lumber that can be shipped as few as 3 days later by this process. The lumber is in inventory for a minimum time, capital is tied up for a minimum time, lumber quality and appearance is the highest possible, energy usage is at a minimum, storage space, required yard space is at the minimum.
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Re: Cooling, Pressure, and Caps

Postby lazyuniondriver » Sun Oct 28, 2012 2:47 pm

Actually far from being off topic as one of the educational links I provided previously stated that industry utilizes "pressure cooking" , in this case, RF cooking under vacuum, to speed manufacturing processes but didn't give an example, you did. Very interesting.
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Re: Cooling, Pressure, and Caps

Postby challenger » Sun Oct 28, 2012 3:14 pm

The discussion on pressurized cooling systems is all valid and interesting, but I still wonder how many work situations today's Cubs are subjected to that necessitates gaining a few more degrees of cooling capacity beyond that provided by the unpressurized system. The most important items are making sure your radiator and internal engine water jacket are clean, using a good rust inhibitor anti-freeze, and maintaining the proper coolant level in the radiator. Considering the age of the Cub, including the radiator and gaskets, it is my opinion that most owners will experience less trouble overall if they stay away from pressurizing their system.
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