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Old 06-04-2009, 10:16 AM
Enright3 Enright3 is offline
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Plumbers: Can you determine if an expansion tank is bad?

So my 20 year old house began having a myriad of problem over the Memorial Day weekend. While the plumber (assigned by the *home warranty people) was at the house fixing an unrelated problem he looked at my water heater and said that it had a parts recall on it, and while I was at it, I should buy a new expansion tank because ours was bad.

Fast forward a couple of days, I call MY plumber to install the recall part on the water heater, and the new expansion tank that I bought.

My plumber agreed it was probably a good idea to change the expansion tank, but that he personally didn't know of any way to determine if it was bad, short of cutting it open.

So, what's the straight dope? What my plumber told me made a lot more sense at the time. The home warranty's plumber just didn't seem 100%. Me: "How do you know it's bad?" HWP: (tapping on expansion tank) "It's got water in it. I can just tell."

um... isn't that the purpose of an expansion tank?
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Old 06-04-2009, 11:08 AM
Harmonious Discord Harmonious Discord is offline
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The top has a standard air valve like on a tire. You can use an air gauge on it to determine the current pressure. The tank should tell you what the air bladder is to be inflated to. If water bleeds out the air valve then your need a new one.
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Old 06-04-2009, 11:22 AM
Enright3 Enright3 is offline
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Quote:
Originally Posted by Harmonious Discord View Post
The top has a standard air valve like on a tire. You can use an air gauge on it to determine the current pressure. The tank should tell you what the air bladder is to be inflated to. If water bleeds out the air valve then your need a new one.
Well, I don't recall him doing that...
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Old 06-04-2009, 01:40 PM
hroark2112 hroark2112 is offline
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Only a few things happen when an expansion tank goes bad.

First, like the person above said, if the rubber bladder in the tank leaks, when you press on the air bleeded valve on top of the tank (looks like the thing on bicycle tires), water will come out.

Second, and less easily diagnosed unless you happen to be a plumber who has been driven NUTS by this issue once, little black flecks will start to appear, normally noticed in the toilet tanks and when you flush the toilet. They will clog aerators on faucets and shower heads as well, but mostly people see it in the toilet. That means the rubber is flaking off and going back into the piping.

Third, if it leaks, replace it.

Short of those above, I don't know of any way it can be diagnosed. I have heard of "parts sellers" telling people they need a new one and it will cost $150, just to make a sale and extra cash.
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  #5  
Old 06-04-2009, 02:59 PM
Moonshiner Moonshiner is offline
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Is this a large expansion tank for a well or a small expansion tank near the water heater?
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  #6  
Old 06-04-2009, 05:01 PM
boytyperanma boytyperanma is offline
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One note. I am not a plumber. I am a well water professional. I operate under a different license. A well drilling license in my state covers the requirements for all well water related work. My scope of things covers everything from where the water comes from to the main shut off after the pressure tank. A plumbers scope of things starts after that shut off. While I sometimes work on things after the shut off that is where my expertise ends. The same goes for plumbers. The pumps and pressure tanks are certainly things they may understand and even work on but they should not be assumed to be experts.

That said he is probably correct.

Quote:
The top has a standard air valve like on a tire. You can use an air gauge on it to determine the current pressure. The tank should tell you what the air bladder is to be inflated to. If water bleeds out the air valve then your need a new one.
If water is coming out the air valve the problem has gone on for far to long. Someone is probably there looking at it because the pump or switch has burnt out.

A expansion tank has a rubber diaphragm in it. It is like a balloon. When the there is no water pressure on it that balloon occupies the whole tank. If you shut off the pump and open a faucet the balloon should force out all the water. I assume this is what he did. When you check the tank in those conditions and there is still water in it that indicates a problem. If water leaks into the balloon or there is a hole in the balloon it can cause a number of problems.

The most common problem is the pump will short cycle.

Pumps operate with a cut in and cut out pressure. Say your system is set at 40/60. You run water, the air in the tank will expand lowering the pressure it is pressing on the water. When there is only 40 pounds of pressure on the water, the pump turns on. The pump will run until it has forced enough water against the air to create 60 pounds of pressure, at that point the pump shuts off. Airs ability to be compressed is what makes the system work.

Water does not compress. If your tank has no air in it, the pressure in your system would near instantly drop below 40 pounds of pressure any time you ran water and reach 60 pounds of pressure very shortly after turning the water off. The pump turning on and off rapidly or too frequently is bad for all parts of the system and will cause premature failures in switches motors pumps plumbing etc. The longer the cycle of staying off or running the healthier it is for the pump.

When it comes to pressure tanks bigger is better. If your replacing the tank go with the largest size you can fit in the given area.
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