Hot Water Expansion Tank

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Old 02-25-09, 05:11 PM
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Hot Water Expansion Tank

I installed an expansion tank about a year ago on the cold water side of the hot water heater. Do I need to check the air pressure on that tank yearly, I think it suppose to be 40psi. I have not checked it yet and if it is low do I need to get it back to 40psi. thx gk
 
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Old 02-25-09, 08:56 PM
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Hi, You can check the pressure as often as you wish, but the proper way and most accurate way to do this is to shut off the water main first and draw off the water pressure till you get to zero psi, then with a tire gauge, check the fitting on the bottom of the tank. If any water comes out, the tank is junk. The pressure should be set at 3 psi under the static water pressure of the house. In other words, you should take a reading of the water pressure of the house with nothing running, then set the expansion tank 3psi under that. I would not worry about checking it every year myself, but you can if you wish.
 
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Old 02-26-09, 03:40 PM
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Thanks, that is a plan. george
 
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Old 02-26-09, 10:58 PM
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What is the rationale for setting the bladder pressure 3 psi under the the static water pressure? Doing so would mean the "nominal" water pressure would be compressing the bladder (i.e. filling the expansion tank) leaving less room for expansion caused by thermal expansion.

Furthermore, most gauges used for testing static pressure will have a 0-200 psi range with +/- 2% error. That means the error alone can be as much as 4 psi. The accuracy (although perhaps not the repeatability) of a tire pressure gauge is probably worse yet.

If at all possible I would prefer to use the same gauge to measure both the bladder pressure and the water pressure. This way the inaccuracies of the gauge are irrelevant. I would also have the bladder pressure equal to, or slightly more than the nominal water pressure to allow for the full capacity of the expansion tank.
 
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Old 02-27-09, 04:13 PM
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i agree 100% with furd on this. the other poster might be thinking of a pressure tank insted of an expansion tank
 
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Old 02-27-09, 06:16 PM
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This is what I'm going to do,
1) Let the pressure off of the house plumbing.
2) Check for any water inside of the expansion tank
3) The directions says, pressure should be 40psi, I found them the other day after the posting
4) Pressurize to 40 psi if needed.
 
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Old 02-27-09, 07:53 PM
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Hello again clockmaker,

I do not know the brand of thermal expansion tank you are using, but I was working for a meter and backflow installation and repair company, and we needed to install thermal expansion tanks on every home where we installed a meter, which was in the thousands while I worked for them.
We used a brand called Amtrol, which is a good and very common brand in my area.
I was told we had to set the pressure 2-3psi under the static pressure of the home. I will admit I did this because I was told to, BUT, the reason I was told this, is it is written in the instructions verbatum like this:

Pre-Installation
1. Remove plastic cap from air valve.
2. Adjust pre-charge to equal incoming pressure.
3. Replace and tighten plastic cap on air valve.

Here is the link to the instruction sheet

http://www.amtrol.com/pdf/9015-087revDTXT.pdf

So according to these instructions the 2-3psi under is not a big concern, but setting to the equal incoming pressure does not necessarily mean 40psi either. If your water pressure is 80psi and you leave the tank set at 40psi, you will not get full range of the tank capabilities and could cause a high pressure condition even with the tank in place.

Thank you furd for bringing this to my attention. I also feel after reading this a few pounds in either direction will not make too much difference, just large pressure differences will.

They also recommend testing yearly, so that would be to your disgretion.

Thank you, Mark
 
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Old 02-28-09, 04:20 AM
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Pre-Installation
1. Remove plastic cap from air valve.
2. Adjust pre-charge to equal incoming pressure.
3. Replace and tighten plastic cap on air valve.


My pressure is 55psi on the lines, so the pre charge pressure would be 55psi. thanks gk
 
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Old 02-28-09, 06:01 AM
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That is correct. Good luck, Mark

Originally Posted by clockmaker View Post
Pre-Installation
1. Remove plastic cap from air valve.
2. Adjust pre-charge to equal incoming pressure.
3. Replace and tighten plastic cap on air valve.


My pressure is 55psi on the lines, so the pre charge pressure would be 55psi. thanks gk
 
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Old 03-08-09, 10:11 AM
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On mine, I tend to tap on the tank about once a month to make sure that the "top" half is filled with air - some day, I know the rubber diaphragm will fail and the top half will get waterlogged.

I also recently changed the piping to mine so that I can suspend the tank horizontally from the joists above, by way of 2 metal straps. I like to make sure that when (not if) the thing eventually fills up with water that it will be able to be adequately suspended even if it gets heavy due to the water in the tank. (The old setup, done by a plumber, had the tank suspended vertically, with the tank above the pipes, with no support other than the copper pipe itself - a setup for a huge leak if the tank got waterlogged.)
 
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Old 03-09-09, 10:21 AM
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you are correct but instead of redoing the thing i would have just added the straps to the vertical piping. it does not matter which direction you install the tank as long as it is supported by something other than the piping.
 
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Old 03-09-09, 03:31 PM
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Originally Posted by 400E View Post
On mine, I tend to tap on the tank about once a month to make sure that the "top" half is filled with air - some day, I know the rubber diaphragm will fail and the top half will get waterlogged.

I also recently changed the piping to mine so that I can suspend the tank horizontally from the joists above, by way of 2 metal straps. I like to make sure that when (not if) the thing eventually fills up with water that it will be able to be adequately suspended even if it gets heavy due to the water in the tank. (The old setup, done by a plumber, had the tank suspended vertically, with the tank above the pipes, with no support other than the copper pipe itself - a setup for a huge leak if the tank got waterlogged.)
That is how I supported mine, between to floor joists and 2 straps. There are times though I hear a thud when the pressure drops on the line due to water useage. I think it is the diaphram flexing inside the tank, but since I put 55psi on the tank there thud has stopped. ALso, my shower has stopped dripping as well as I have mentioned in another post here. thx gk
 
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