Radiator / furnace problem

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Edwin Pawlowski wrote:

I've not followed the whole thread, but if OP continues to add water indefinitely and pressure continues to drop and never recovers, the system _eventually_ would have to fill solid if the water isn't going somewhere...it is, after all a finite volume.
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*Exactly* the same problem? Including the need to repeatedly purge air from the system?

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Doug Miller (alphageek at milmac dot com)
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I did say "the same problem" didn't I?
I had a problem this past winder with the packing nut on the feed valve. I didn't get around to fixing it for some time, but it did not leak when turned off. The noise from air in the system was very loud, especially after being off all night and going back on first thing in the morning. It woke me before the alarm went off. I finally replaced the valve, left it open, problem went away once the air self purged. There is a valve on top of the Extrol expansion tank for this purpose.
Sorry if my real life factual situation differs from your opinion. The feed valve is still open, but I'll probably close it until heating seasons starts again. Then it will be open, same as it has been for the 29 years this house has existed.
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Ed
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I'm not questioning your experiences -- I just don't think that you've quite understood the OP's situation. As you said, it's perfectly normal for the pressure to go up or down due to expansion and contraction as the system cycles on and off. What's *not* normal is the need for frequent bleeding and replenishment.
OTOH, if you're having to purge air, and add water, every few days like the OP does, then -- I'm sorry, but you have a leak too. A properly functioning hydronic system has no need for frequent air bleeding and water replenishment.
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Doug Miller (alphageek at milmac dot com)
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No, Doug, I don't have a leak. All my tubing is either visible or in a place a leak would be evident, especially after 25 years. No pipes or tubing in concrete. You are welcome to come and inspect at any time.
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And do you tell me that you have to purge air, and add water, every few days?
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Doug Miller (alphageek at milmac dot com)
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Not if I leave the feed water valve open. No pair to purge then. Only after it has been closed and runs a couple of cycles. I'm sure you'd like to see this in operation. What time can I expect you? Bring your leak detector.
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Water doesn't just disappear. If you have to keep putting water in, that means water is getting out.
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Doug Miller (alphageek at milmac dot com)
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As the water cools, it contracts and air is sucked in to replace it. If the system is sealed, a bladder tank is going to counteract these actions in a perfect world. In an imperfect world air gets sucked in. I know what works for me. I know I have no leaks.
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If you have to keep putting water in, that means it's getting out somehow. Your last sentence should be revised to "I have no leaks that I know of."
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Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

I keep wondering how the system keeps cooling water indefinitely w/o it finally freezing solid... :)
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The heat is not on. The valve is open. No water has passed. The invitation is open for you to come and search for the alleged leaks. I'd bet you money, lots of money on that. Here is your chance to make thousands of dollars, just by finding a simple leak.
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You don't have an air buffer. What do you think the purpose of the expansion tank is? It's supposed to have air in it. If you'd quit letting the air out of it, then your problem might take care of itself.
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I'm not letting air out of the tank, it is in the water side of the system. The only way to expel air is to add water or something else to replace it. The expansion tank is to allow for the change in volume of the water as the temperature changes, but does nothing to expel air from the copper tubing. I'm sure you know better.
http://www.watts.com/pro/_productsFull_tree.asp?catIdd&parCat%1&pidf4&ref=2 Description: Series FV-4M1 Automatic Vent Valves are used in commercial and residential hydronic heating applications to provide automatic air venting for hot or cold water distribution systems. It consists of a brass body construction with female NPT connection, brass cover, air vent with silicone rubber seal, polyethylene float with valve plug, and automatic vent. Series FV-4M1 has a high temperature rating and is ideal for use with glycol systems or for use as an anti-vacuum device. It can also be installed to permit the separation and dispersal of air while fluid is circulating in the system. Can be disassembled for inspection and cleaning. Maximum Pressure: 150psi (10 bar).
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If the expansion valve is correctly sized, and correctly charged with air, then the system will never drop into a vacuum, and thus never suck in air. Under and overpressurization is the very purpose of the expansion tank. If yours doesn't work, then the solution is to fix it, not to shut off the make-up valve. Shutting off the valve will introduce problems of its own. As air bleeds off through the airtrol valves (or equivalent) then the valve must be open in order to allow the pressure in the system to be maintained at the regulator setting. With it closed, all of the air in the expansion tank will begin to bleed out of the system as it diffuses into the water, where it makes its way to the airtrol valves. The pressure in the system will steadily drop until the low side is at or below atmospheric. After that air will be sucked into the system and subsequently released from it during each full heating and cooldown cycle. Water will then have to be added to the system manually, and the air cushion in the expansion tank reset. Where the water is leaving the system is at the expansion tank, i.e. when you blow it down to refill it with air.
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In retrospect, I think you said that you only had problems when the valve was closed. In that case, what I went over above is why you had problems before, i.e. with the valve closed. The valve is supposed to be open, so you didn't do anything special to your system, you only set it back the way it was supposed to be. Pardon the oversight.
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Thank you for a good explanation. I keep my valve open.
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If no water has passed, then you're not adding water.

The system has a finite volume. It is simply impossible to keep adding water to a finite volume, unless it's getting out somehow.
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Doug Miller (alphageek at milmac dot com)
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Not so much adding water as it is eliminating air Taco makes valves to eliminate air http://www.taco-hvac.com/en/products/Air+Vents/products.html?current_category
Once air is in the system, it must be purged. The only way to truly purge the air it to keep the feed water valve open to replace the air that is moved out of the system. If the system is opened for any reason, repair a circulator, change a fitting, whatever, air is introduced. Simply opening a drain does not eliminate it all,
Air, or course, has greater compressibility so when the water expands it easily compresses the air. Some will be eliminated by the Taco valve, but some will still be getting by if there is no feed water to take its place. Once the system cools, the air is still there and with the pressure drop it may even be possible to draw in more. As you introduce fresh water, you are also introducing dissolved oxygen, thus making the air problem worse.
The only way to finally eliminate all the air is to keep the feed water valve open until all the air is purged from the system. It may take some days depending on the number of cycles, temperature, size of system. If you keep closing the valve, you will never evacuate all the air. Having air in the system does NOT mean you have a leak.
I replaced a circulator a few months back. It took two or three days for the air to finally be fully evacuated and the heating system to be quiet again when circulating.
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Yes, I know. I understand all that. My point is simply that if you keep having to add water, over and over and over and over, there *must* be a leak somewhere.
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Doug Miller (alphageek at milmac dot com)
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