Can oil be used in an expantion tank to prevent O2

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Old 12-07-07, 06:40 AM
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Can oil be used in an expantion tank to prevent O2

I have been reading about problems that oxygen cause in a system with an open expantion tank. I had the idea of using a layer of oil in the tank to seperate the water from the oxygen in the air. I guess the first question would be can oxygen pass through oil? That may kill the idea right there. I cant be the first person with this idea. Maybe it was tried 100+ years ago. Maybe a large diameter float in the tank that would cover most of the surface area may work better. Has anything like this been tried?
 
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Old 12-07-07, 01:50 PM
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You get points for thinking, unfortunately your thinking in this case is flawed.

Oil in the expansion tank could get into the boiler where it will work as an insulator and cause parts of the boiler to overheat. Or if it got into the circulating water it would insulate the heat emitters decreasing the efficacy of the system.

What is done in commercial and industrial sized systems is to use a nitrogen blanket rather than air in the expansion tank. Unfortunately this is not practical in residential systems.

Your best bet is to use a diaphragm type (also known as a bladder type) expansion tank.
 
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Old 12-07-07, 02:14 PM
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Hi. Is this an open loop or closed loop system? If it is closed loop, why is there oxygen getting into the system to cause a problem? Are they vents on the system, a problem with excess makeup water being added? If it is open loop, why do you need a tank?

Pete
 
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Old 12-07-07, 06:49 PM
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This would be for an open atmospheric gravity flow hot water system. As I have read that oxygen in the water causes oxidation, the only place oxygen could get in is thru the expantion tank vent. When sauerkraut is made a board is cut to closly fit the inside of the crock. This keeps the air off of the kraut. Or think of a fish bowl. If it is filled to the top there is less surface area to absorb oxygen than if it is filled half way, at the widest piont of the bowl. This lead me to think if the surface of the water in an open tank were covered, maybe with a float, this would greatly reduce the oxygen absorbtion. Air bubbles would still be able to escape around the float. I suppose oil would work great if it never got into the system. But if it ever did it would be a major problem, worse than oxygen.
 
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Old 12-11-07, 09:04 PM
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I personally don't have a fish bowl, but I have fish in an aquarium. By the way my fish don't like kraut. I do have a crock in the backyard though but he doesn't like kraut either but he likes fish. The crock can float pretty well, and I kind of wonder if it's the air bubbles escaping out of the back end after eating the fish that lets him defy gravity to be more specific. Couldn't resist this guys, oil, oxygen, nuclear reactors, yeh, ok
 
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Old 12-12-07, 11:51 AM
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First things first. If you have an open system to atmosphere it should be converted to a closed system. The O2 you are getting into the system is not good. Operating a closed system is beneficial in a lot of ways. Convert to a bladder type tank or non-bladder type tank between the floor joists. Either one is good. I prefer the non-bladder type tank. When it is properly installed there is no maintenance. No checking the air charge, checking for water below the bladder and of course no draining. Service free. A bladder type tank you must check pressure, and to do this means dropping system pressure to 0, adding pressure when needed and replacing when the bladder goes bad.
 
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