Water dripping from expansion tank

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LindaPinda

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Up to my eyeballs in another project, I walked into the garage to discover water on the floor. Traced it to a drip from the "water heater safety tank" on my gas water heater. Some googling later, I see that (a) the pressure relief valve I've replaced twice might have only been a symptom of the tank going bad; and (b) I may need to replace that expansion tank.

I recall that at some point in the distant past I noticed a very thin line of rust running down the side of the tank (it's installed inverted, so that the air valve is on top--I can't even see the air valve without getting on a ladder) and evidence that water had once dripped out, but since I know nothing about this stuff and it didn't seem to be dripping in any way then, I ignored it. That was years ago (literally), but today it's dripping at a rate of about 1 drop/second.

I've rigged a lovely contraption to catch the dripping water in a bucket. Does this need to be dealt with IMMEDIATELY or can I do the collect-and-empty-the-bucket routine for a few days until I have time to deal?

Also, once there's water coming out of the air valve, is there any hope of redeeming the thing by draining and re-pressurizing or should I just plan on replacing it? I'm poor so any options for realistically saving money are appreciated. Thanks.

expansion-tank-leak-2.jpg
 
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Reach4

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If there is water coming out of the valve on the tank, that is unusual. Not only should the diaphram/bladder stop the water, the valve core should stop the water if you are not pressing the center of the stem.

Replace that tank. No redemption.

You can just keep emptying the bucket for as long as you like.
 

Jadnashua

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By your ET leaking, it may be enough to prevent your WH's T&P safety valve from opening, but it will still be subjecting the piping system to excessive pressure (depending on how fast the leak is).

An ET is quick and easy to replace, but if it is standing up like that, and it fails, it can be putting a lot of pressure (via weight) on the pipe supporting it. It really needs some support. It's light when in use, but full of water when it fails. You need to know your static water pressure to precharge the tank before you install it. It should be precharged to 1-2# less than the static, normal water pressure in the house. They typically come precharged to around 40psi, but that can vary, and it's unlikely your home's water pressure is exactly that. If it is too low, that flexes the bladder more than it is designed for, and it will fail sooner.
 

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being in the garage it is not as critical as it would be in the basement of your home..

you probably should change the tank sometime soon..
.your tank will rust out and get worse over time...I have seen the horror of a few of them actually
blowing out a penny sized hole and flooding the hell out of basements before....:eek::eek:

WARNING your tank is probably water logged so it will weigh upwards of 40 lbs
if it is the larger one.... it is .just waiting to drop into your lap be careful

almost any average moron can unscrew it and install a new one ...
1. turn off the water and de-pressurize the hot side of the system..
2. to unscrew the tank you wrench and turn it counter clockwise ....
.usually this will go easy but you will probably take a bath while doing this...
3. do not let the 40lb waterlogged tank drop on your foot..
it hurts real bad when that happens:D

4. pump up the new tank to about 85psi and put dope on the threads..
screw it into the socket turning clockwise... do not cross thread..
5 turn water back on and check for leaks...

therm-x-trol-rust-2.jpg
 
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Jadnashua

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Ideally, the internal air pressure should be the same as the static water pressure. This puts the bladder in its 'neutral' position. Pre-charging it higher, it will almost always be stretched, and won't last as long. Now, if the air valve leaks, it might give you satisfactory performance a bit longer before you should charge it back up again, but it won't help it live longer. FWIW, your home's water pressure should NEVER exceed 80psi by code. The ET is designed to help prevent that when you have a closed system.
 

Reach4

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Ideally, the internal air pressure should be the same as the static water pressure. This puts the bladder in its 'neutral' position. Pre-charging it higher, it will almost always be stretched, and won't last as long. Now, if the air valve leaks, it might give you satisfactory performance a bit longer before you should charge it back up again, but it won't help it live longer. FWIW, your home's water pressure should NEVER exceed 80psi by code. The ET is designed to help prevent that when you have a closed system.

You got your first sentence right. At that pressure, the bladder will be in the same position it would be in if you set the precharge 10 or 20 PSI higher than the incoming pressure. It will be in the same position that it is in when shipped empty with 40 or 50 PSI pre-charge.
 

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At least on the Watts tanks, exceeding 80psi precharge voids the warranty. http://media.wattswater.com/2915054.pdf If you read steps 1-2, they say to set the pre-charge to the static water pressure, essentially what I said. One would think that the manufacturer has a clue on how they work and how best to install them.
 

Reach4

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At least on the Watts tanks, exceeding 80psi precharge voids the warranty. http://media.wattswater.com/2915054.pdf If you read steps 1-2, they say to set the pre-charge to the static water pressure, essentially what I said.
That pre-charge pressure is what you said in sentence one of reply 5. Then you went off track such as with your "neutral position" bit. Your pre-charge advice improved from what you said in reply 2.

And regarding the pre-charge, suppose the city water was 40 PSI in the day and 50 PSI at 4 AM. I would think it to be better to set the pre-charge to 50 PSI.

http://www.flexconind.com/pdf/wh-whv_install.pdf shows Flexcon expansion tanks have "Maximum Working Pressure 150 PSI". http://www.watts.com/pages/_products_details.asp?pid=852 says "Maximum Pressure: 150psi (10 bar)" I interpret that such that if the precharge is at 80, but the thermal expansion raises the pressure to 100 PSI, that is OK with the pressure tanks. It does exceed what many toilet fill valves are specified to, but I expect no problem typically if 100 PSI were to occur due to thermal expansion. Of course I would prefer to set the precharge to 60 if the water pressure from the city or PRV is 60. If you set the precharge to 60 and the city or PRV only delivers 45 PSI, no harm will come to the pressure tank as a consequence -- at least that's how I see it.
 
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Jadnashua

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Me thinks you are missing the whole point of an expansion tank! The idea is that the air compresses whereas the water doesn't, so when the water expands, there is someplace to go. The air pressure and therefore the water pressure do NOT go up significantly when the WH is running...that is the entire reason for installing one in the first place...it helps keep the water pressure fairly constant. Water, OTOH, in hard pipes, do not appreciably expand to accommodate any expansion of the hot water, and the pressure DOES go up very quickly.

If your night-time water pressure rises too much, maybe the better thing is to install a PRV, then it's constant, but I suppose, you could compromise at maybe 45psi, half way between your daytime and nighttime water pressures.
 

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Me thinks you are missing the whole point of an expansion tank!
Forsooth! I, of course, think you are spouting *. Would you care to indicate something I said on his thread that is inaccurate? The purpose of the pressure tank is to keep the water pressure from rising too high in the face of what is effectively a 1-way valve on the incoming water and the fact that water expands with temperature. The purpose of the precharge is to help a given size of tank to hold more expansion water , keeping the water pressure safely under 80 PSI, without excessively stretching out the diaphragm. The diaphragm is not stretched by having a precharge higher than the static water pressure. As I see it, a precharge at the highest incoming pressure, or even a little above, will minimize the diaphragm stretching. I post inaccurate things at times, but I try to recognize and admit them.

And in the case of an example city system that varies between the 40 and 50 normally, what downside do you see to a precharge of 50 compared to 45 PSI? If the pressure tank is bigger than necessary, the difference is minimal. If the tank were just big enough, I think the higher precharge is better for tank life by minimizing the diaphragm stretching.
 

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When the pre-charge is higher than the incoming water pressure, and you have thermal expansion, the pipe water pressure will rise very quickly to the pre-charged level, then become stable as the bladder cannot be compressed until the water pressure gets higher than the pre-charged level. The ET cannot overcome variations in the supply water pressure. The instructions from Watts say to size it for your max value in their calculator, whereas their installation instructions say to pre-charge it for the observed water pressure. If your pressure varies, you'd want to size your ET for the higher pressure, as the instructions say. In this case, if you pre-charged it for 50psi, and the incoming water pressure was 40, when the WH started heating, it would almost immediately jump to 50psi, then the pressure would remain fairly stable. One of the big reasons for installing an ET is to keep the pressure stable and not to trigger the T&P valve. If your static pressure does not exceed 80psi, the ET will still work. The more it expands and contracts, just like anything, that movement will cause it to wear out faster. So, adjust it to the static pressure, but size it for the maximum pressure, and the differences won't be much, and you'll be following the manufacturer's recommendations.

What I would not do, is pre-charge it for 85psi, as was recommended (which voids the warranty), as then, your water pressure will always spike to 85psi before it becomes stable during any WH heating cycle after water use.

If you pre-charge higher than the normal water pressure, when the WH runs after use, the water pressure spikes, then water at that pressure gets stored in the ET. Now, open up a tap, and you get a spurt of water at the higher pressure until the ET equalizes. Say you set it to 85psi, and your normal water pressure was 40psi, after heating water and the resulting expanded water gets stored in the tank, you get a spurt of that 85psi (or whatever pressure you set your tank to) until the bladder normalizes...just like a well storage tank. Now, say you pre-charged it to 40psi, your WH runs, the pressure is still 40psi. Take that overnight when it hits 50psi, it will stay at 50psi after expansion, and you will not get a spurt of higher pressure water when you open a tap. The bladder won't be moving around as much.
 
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Master Plumber Mark

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if you dont pre-charge the expansion tank to about 85 psi then you basically have
only a storage tank... for more water... and that is all it will ever be ...
There must be some resistance that the pressure and spike in the water has
to come up against to work for THERMAL EXPANSION...

thermal expansion tanks are only good for the warranty periiod of your water heater...
if you are lucky..... most times we find them totally waterlogged and completely useless
because no one checks to see if the pressure has leaked out of the bladder and they go back
to NEUTRAL......
 

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If your water never goes above 50 with a faucet dribbling (to take care of any thermal expansion during measurement) and your precharge is set to 50 or 60, your pressure tank is empty when it does not contain water due to thermal expansion. The tank is as empty as if the precharge was set for 85. I could see that maybe a higher precharge is more useful when you have a PRV than when you need a tank just because a check valve being built into the new water meter.

85 has what appears to be problem with the water pressure maybe going to 100 or more, depending on the sizing of the tanks and water heaters. Yes, the water pressure will drop quickly once some water is used. How much of a problem is 100 PSI? Probably typically none, but it does exceed what toilet fill valves are specified to. Still, I acknowledge that this is typically not going to be a problem.

I agree that it is better to have the precharge set a little high than a little low-- particularly if the expansion tank is the minimum size.

Fortunately I don't need a separate water heater expansion tank. But if I had one, I would be highly disappointed if it only lasted as long as a water heater warranty. Heck, I would be very disappointed if the water heater only lasted that long. I am used to water heaters lasting over 20 years, but those are not new condensing units. Anyway, if life on tanks is limited, I would consider using a Therm-X-trol ST-12 4.4 gallon expansion tank if I were to need a tank, even if the tables said that a 2 gallon ST-5 was sufficient. I presume that the Therm-X-Trol tanks are better made.

My thoughts on the subject are not based on experience.
 

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When your air pressure is set to the normal water pressure, the bladder is exactly where the manufacturer designed it to be for maximum life. If you set it to 85psi (above at least Watts maximum allowed and voiding the warranty), the bladder will not move until the water pressure gets to 85psi, WHICH IS ABOVE THE MAX RECOMMENDED FOR ANY RESIDENTIAL PLUMBING. It WILL get that high unless something is leaking in a closed system since copper pipes just do not expand until you get to LOTS more pressure than that. Now, depending on how much water you've heated, and how much temperature change, the volume may only be a cup or two. So, the bladder won't move much.

When I was young, before my father installed a PRV, we had really high water pressure. I remember more than once almost having the glass pushed out of my hand when trying to fill it at the sink (that was before flow restrictors were mandated on sink faucets). High pressure is an issue. Your WH's porcelain lining doesn't like pressure changes, either. Setting your expansion tank's pressure to the nominal water pressure means it won't see as much stress. Nobody's ET lasts forever, and if you need one, it behooves you to actually do a little PM on it once in awhile. Most people don't. Your washing machine hoses, toilet supply hose, and any other hose in the home does not like pressure cycling...an ET, properly set, protects them all. Set it properly, do a little PM once in awhile, and things work. WHen it fails, replace it. The first thing you'll tend to notice is either it is leaking (long since failed), or the T&P valve weeps after using some hot water as the WH cycles on. WHen that drains outside, rather than somewhere maybe more visible, that telltale sign can easily be missed.

Setting the pre-charge to 85psi is a copout IMHO. It doesn't do what it is supposed to do when that is done, keep the pressure steady without spikes, and, as mentioned, that is above the code limit of 80psi for residential plumbing. Why force it to get above that on a daily basis? Just seems wrong to me.
 

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I have 110 psi coming into my home... I have a PRV set at 70spi.. My thermal expansion tank is set at 80psi....
so when the water heater has some thermal expansion to do it has something to expand against at that time....

A PRV valve has a tendency to creep up or leak pressure through it during the night and can rise dramatically over the
night

you can do whatever you wish to but this is not voodo or black majic... If you dont set the therm tank to at least a
slightly higher setting than your in-coming pressure, it is basically a worthless water-logged appliance.

good luck...
 

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The size of the bladder when set to the designed pressure (that of your typical WP), has a design 'acceptance' volume. You set that based on the WH size, the temperature rise, and then, it will accept the design volume. If it becomes a 'worthless water-logged appliance', it is defective to start with.

One might use the same argument about your car's tires...put in an extra 10-20# or more so that you can go longer before they become so soft they're unsafe. Hassle is, too much is as bad or worse than not enough. Install it as designed, check it periodically like you should your car tires, and you'll know when it is shot and, it will do what it was designed to do. The fallacy in Mark's comment is that he assumes the static pressure means the air bladder in the tank is totally compressed, and there's no room for expansion. This is blatantly wrong. Look at the acceptance volume in the linked spec sheet http://media.wattswater.com/ES-PLT.pdf. By pre-charging to the proper pressure, you are more likely to get the designed life out of the thing and not get a large volume of water stored in the tank to spurt out of the tank when you eventually open a valve somewhere.

The actual pressure in the bladder (air) side of the ET will ALWAYS become the same as the WP, once the WP exceeds the static pressure. IOW, as you try to compress the bladder, the air pressure rises, and always follows the water pressure applied. So, if your pre-charge was 80psi, and your static pressure went up to 110psi, the air pressure would become 110psi. Since water doesn't compress, when you get expansion, the pressure will immediately spike to the setting of the ET, and then, as the air is compressed, contain the water pressure from rising. The only way it would continue to rise is if the ET failed, since you cannot compress the air stored in there enough to make the volume go to zero unless you've not sized it properly ,or you have a defective tank.

The science is not voodoo, nor magic. Exceeding the manufacturer's max pre-charge pressure is just wrong...fix the supply side.

If your PRV creeps, it's time for maintenance or replacement, not a patch.
 
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