Water heater expansion tank pressure question

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I am replacing my water heater expansion tank. It is leaking at the weld (piece of carp). Anyway my question assumes the following:
H2O pressure measured at hose bib: 80 PSI System pressure recommended by expansion tank mfr: 60 PSI New tank max PSI: 100
My questions: Do I just add more air to get to 80 PSI? Is a small electric tire compressor ok or must it be a hand/tire pump?
TIA
Rob
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If the water pressure is 80 PSI then it will pressurize any entrapped air to the same pressure. You do not need to put any air in. Even if you managed to get all the air out the system pressure would be the water pressure...80 psi.
EJ in NJ
snipped-for-privacy@gmail.com wrote:

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Ernie, You are a freakin idiot. You pressurize the new tank to match the pressure of the incoming water to the home. With your thinking, why would they even put ANY air in the tank at all. How you pump the tank up makes no difference. Just match it to the psi in your home. Bubba
On Sat, 13 Dec 2008 22:19:34 -0500, Ernie Willson

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Here you go... http://www.watts.com/pdf/1915356.pdf step-by-step instruction for adjusting the pre-charge of a potable water thermal expansion tank.
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Bubba-
Thanks for the additional info. I just went out and checked the tank...no change from the factory charge. Eddie wasn't as helpful as he could have been, that's for sure. Why would someone reply with a wrong answer... Damn newsgroups aren't what they once were. I'm headed out to get some type of pump. Then, I'll come back and turn off the water, discharge the system then, re-pressurize.
What pissed me off more was when I called the local water utility to find out what the pressure might be. He said it varies from meter to meter call a plumber. After he asked for my address. A $10 gauge from the underground sprinkler system gave me the answer.
All in all I figure this probably saved me from a plumber's overtime/ weekend rates.
Rob

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On Sun, 14 Dec 2008 10:47:18 -0800 (PST), " snipped-for-privacy@gmail.com"

Rob, No problem. Its a shame there are idiots like Ernie and JIMMIE in here. I dont understand it either why someone answers with the wrong crap. Either they are just total morons or they just like futzing up the group. The pressure does vary a bit from meter to meter. Either way, I dont think I'd have called a plumber on the weekend for that. Not exactly an emergency you know? Maybe Ernie and JIMMIE will trip and fall on their big ol noggin tomorrow and knock a little more nonsense into their thick skulls. Sounds like youve got it figured out correctly now. Just remember, If you read it on the internet "Its gotta be true" :-) Bubba

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Bubba-
Thanks again. "If you read it on the internet "Its gotta be true"...exactly what I was thinking as I was going to check the pressure the first time and found it still at the factory charge. LOL!
Rob
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wrote:

http://www.griffithengineering.net/services/aspe_newsletters/Thermal_Expansion_Tanks_revised.pdf
Mark
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snipped-for-privacy@gmail.com wrote:

Actually the water company gave you the correct answer. It varies as to where you are in the system and also changes according to system usage. When you measured your pressure you simply saw the pressure at that particular time.

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Ernie-
I installed the new tank and turned the water back on. The system didn't pressurize itself. I'm going out to get some kind of pump to add the needed pressure.
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wrote:

Ernie-
I installed the new tank and turned the water back on. The system didn't pressurize itself. I'm going out to get some kind of pump to add the needed pressure.
************************************************************
What does that mean? "The system didn't pressurize itself"?
The pressure inside the tank should be identical to the water pressure.
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Bob,
You are completely correct. Thanks for your comment. I'm having difficulty understanding Bubba's "intelligent" comment. People like him make ignorant people look smart.
EJ in NJ
Bob F wrote:

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Ernie said: "If the water pressure is 80 PSI then it will pressurize any entrapped air to the same pressure. You do not need to put any air in. Even if you managed to get all the air out the system pressure would be the water pressure...80 psi. "
The replacement tank was pressurized from the factory to 36 PSI. After installing the tank, turning the water back and running the water for a few minutes... I turned off the water and went back and checked the pressure. It was 36 PSI NOT at the 80 PSI I measured at the hose bib prior to installing the new tank. So, I turned the water off at the main and drained the system. Then, I added pressure to the tank to match the 80 PSI.
Thanks to everyone!

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wrote:

Huh, You shouldnt have had to add any air to it at all. The initial pressure in the tank determines the water to air ratio in the tank during operation.I think anywhere from 1/3 water to 2/3 water is good. The way you have it set up there is almost no water in the tank. You should have measured the pressure with the water on before you screwed with it. That reading would have equaled your water pressure and the tank would have been about half full of water. I got a question, does your system have a backflow preventer. Around here a lot of plumbers install the tanks without the backflow preventer rendering the purpose of the tank useless.
Jimmie
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This is laughable... the facts that detail the installation and proper procedure for setting the air pre-charge for a potable water thermal expansion tank were posted by me earlier in this thread. The link was to Watts, the manufacturer of said tanks and among the largest supplier of plumbing hardware in the US if not the world. They know a little bit about what they do and the code requirements of what they sell.
To all those who think they know more than Watts... read and learn http://www.watts.com/pdf/1915356.pdf
For those seeking to learn about thermal expansion in house plumbing in general here you go... http://www.watts.com/pro/divisions/watersafety_flowcontrol/learnabout/learnabout_thermexpansion.asp?catIdd
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This was posted earlier by someone:
http://www.griffithengineering.net/services/aspe_newsletters/Thermal_Expansion_Tanks_revised.pdf
It is wordy but correct. You, on the other hand, are full of it. Simple to convince yourself - just ask to look at the instructions in any plumbing store.
Tanks will come with a standard pre-charge of around 40 psi and need to have that corrected for the system pressure. You don't go into a store and look for a tank with a 80 psi pre-charge because there will only be ones with 40 psi. Thus there is no 'selection' involved. Only choice you have is "how big a tank".
The amazing thing is that, if it is a new tank, there will be instrctions included that say to pre-charge it to the system pressure and the thread should have been unnecessary.
Harry K
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While true Harry... the reason for this thread was two questions that I as a non plumbing professional posted
"My questions: Do I just add more air to get to 80 PSI? Is a small electric tire compressor ok or must it be a hand/tire pump?"
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wrote:

I don't think either question was answered properly - we all went off on a tangent.
I also believe you have already fixed it but in case you haven't the answeers are:
Yes, just add air up to the system pressure. Any source of pressurized air will do.
Harry K
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best solution would be to regulate the house down a bit. but to answer your question, yes, just air the tank to 80 psi with the water off and the lines discharged.
s

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On Dec 14, 10:02pm, "Steve Barker DLT"

Yes I didnt catch he was running 80 PSI already. I was too interested in the fact he messed with the pre-charge and what he had done to it. I am betting he is working straight off the curb and has no PRV.or backflow preventer. If these things are selected properly to start with you shouldnt have to do anything but plumb them in. The HD and LOWES has a pamplet you can get to help you select the right one. The local mom and pop store will also loan you a pressure guage, deposit required of course.
Jimmie
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