pressure value blowing water again !

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w1ljm

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Hi, We are having a problem with a gas hot water tank (40 gal). Back in 2002 (brand new house 2001) we found that the pressure relief value was blowing water after we took a shower and empting gallons of water on the cellar floor. We had a plumber install a expansion tank and this resolved the problem. Now the cellar floor has gallons of water on it again. I found the pressure value was blowing water again after showers. What else could be causing this problem?
Also ! I noticed that there is a air pressure value (looks like a bike tire air value) on the bottom of the tank. What is this for? Is there suppose to be pressure in the tank at all times or are you suppose to bleed it off? What is the pressure suppose to be? What kind of gauge do you read it with? (bike or car tire gauge)?
 
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Bob NH

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Set the Expansion Tank Pressure

First, check if the tank has failed by letting a little air out of the air valve. If water comes out, the bladder has failed and the tank must be replaced.

If the tank passes the test, you should set the pressure on the air side of the expansion tank as follows.

1. Measure your cold water pressure with no water flowing. If you can't measure it, assume the following: 50 PSI if a municipal system; pressure switch low setting if you have a pump.
2. Shut off the main water supply (NOT the isolation valve to the tank if there is one) on the inlet side of the expansion tank.
3. Open a cold water faucet and let it drain until it stops running. If it doesn't stop running, then you didn't get the water turned off. Leave it open until Step 5.
4. Add air to the bladder to 5 psi LESS than the pressure obtained in Step 1.
5. Close the faucet and turn on the water supply valve.
 

Gary Swart

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The expansion tank has an air value so that it can be set to the same pressure as the water pressure. It likely the expansion tank has failed and needs to be replaced. When it is replaced, you pressurize the tank with a small hand pump. You obviously need to know what the incoming water pressure is, and this can be determined with an inexpensive gauge.
 

w1ljm

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test

I did check the expansion tank. It appears to have not failed. There was no water coming out when I tried to release some air. Problem is that there was not much air to release before the tank had no more to release. Could this be the problem? I am guessing that since the tank had very little air in it, it could not work properly. If following your steps to fill the tank with air, what kind of gauge do I use to check the pressure? Regular car tire pressure gauge? Also (inexpensive gauge) to measure water pressure, is this type of gauge that you are talking about one that screws on to a faucet?
Thank you guys for your help and guidance.
Bob NH said:
First, check if the tank has failed by letting a little air out of the air valve. If water comes out, the bladder has failed and the tank must be replaced.

If the tank passes the test, you should set the pressure on the air side of the expansion tank as follows.

1. Measure your cold water pressure with no water flowing. If you can't measure it, assume the following: 50 PSI if a municipal system; pressure switch low setting if you have a pump.
2. Shut off the main water supply (NOT the isolation valve to the tank if there is one) on the inlet side of the expansion tank.
3. Open a cold water faucet and let it drain until it stops running. If it doesn't stop running, then you didn't get the water turned off. Leave it open until Step 5.
4. Add air to the bladder to 5 psi LESS than the pressure obtained in Step 1.
5. Close the faucet and turn on the water supply valve.
 
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Jadnashua

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Yep, you use a regular tire pressure gauge...and, if it didn't have any air in it, that is the problem. Now, the bigger question is why did it leak out! It could be as simple as the valve cover was not on tight (note, as in a car tire, the primary seal is the cap, not the valve). So, fill it up per the instructions, cap it off tightly, then, check it again in say a week or so. You might have a leaky valve.
 
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