Installed expansion tank now pressure is higher?

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parkp81

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I just got finished installing a expansion tank for my water heater.

Before I did all this I took a Watts water pressure gauge and connected it to a hose spigot, and the reading was at 65 (There is a pressure reducing valve installed). I then pumped the expansion tank to 65 psi, before installing. I decided it was a good time to drain the water from the water heater also, so I did that. I installed the expansion tank and turned everything back on.

A few hours later I went outside to check the water pressure (I left the pressure gauge connected, with the spigot turned on) to see if it was holding at 65, and I noticed the red needle shows the highest the pressure got to was around 52/53.

I assume I have too little pressure in the expansion tank? If so, it must mean the gauge I used is not accurate.
 
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Reach4

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I assume I have too much pressure in the expansion tank? If so, it must mean the gauge I used is not accurate.
Not necessarily. In fact it would be OK to have the expansion tank air pressure (with zero water pressure) a little over 65.

(some editing )
Presuming that you used no water as the WH was heating up the water, that sounds very good. You had almost a worst case of heating ground-temperature water to hot. Heating winter or spring temperature water would have been a harder test, but if you held the peak pressure to 80, that would be quite nice. That cold water heated and expanded. The pressure went up. Sounds like your expansion tank was big enough. You did very well. Edit. I am presuming that if you use a little water, the water pressure will drop back to the PRV setting.
 

parkp81

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Also when adding air to the tank, can I shut off the water main, open a faucet in the house, and check/adjust the pressure without having to remove the tank?
 

Reach4

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Also when adding air to the tank, can I shut off the water main, open a faucet in the house, and check/adjust the pressure without having to remove the tank?
Yes.
 

parkp81

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Not necessarily. In fact it would be OK to have the expansion tank air pressure (with zero water pressure) a little over 65.

Presuming that you used no water as the WH was heating up the water, that sounds very good. You had almost a worst case of heating ground-temperature water to hot. Heating winter or spring temperature water would have been a harder test, but if you held the pressure to 85, that would still be nice. That cold water heated and expanded. The pressure went up. Sounds like your expansion tank was big enough. You did very well. I am presuming that if you use a little water, the water pressure will drop back to about 65.

Sorry I edited the post. For some reason the pressure is now holding at 52/53, checked with all faucets closed, and water heater is not heating up water at the moment.

I guess earlier it was higher than 65, because the water heater was heating up the water, which makes sense.

I guess I will get another gauge tomorrow and check it again. But for now I am going to leave the water pressure gauge connected overnight, and take a look at it tomorrow morning.
 

Reach4

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You edited. Then I edited. Looks good. If you feel like you want more pressure, you could crank up the PRV. But 50 PSI is usually a nice pressure for a house.

If the pressure gauge goes way up, it might not mean the pressure gauge did. Some of the lazy/tattletale hand gauges will respond to vibration. To check for that, tap the dial area. If the needle jumps, that would demonstrate that effect. If the needle does not jump, then then your gauge is not very vibration sensitive.
 

parkp81

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Thanks,

When I installed the PRV I had the water pressure adjusted to 65, which was many months before I installed the expansion tank. I would like the pressure to remain at 65, but it is strange how it got lower after the expansion tank installation?
 

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Thanks,

When I installed the PRV I had the water pressure adjusted to 65, which was many months before I installed the expansion tank. I would like the pressure to remain at 65, but it is strange how it got lower after the expansion tank installation?
Dribble a little water while adjusting the PRV. If the water pressure is higher than the precharge pressure, the air will indicate about the same as the water pressure. The water pressure differs a bit with altitude; pressure drops 0.433 PSI for each foot of altitude. For actual 65 PSI water, I would set the air to maybe 68. 65 would be good too, but the 68 gives you a little margin for gauge mismatch.
 

Flapper

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The red needles on gauges are so loose that they may lie to you (vibrations will move them).
 
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