packy,hate to bother you again but…
I lowered the pressure in the expansion tank as I mention to about the same pressure the PRVs are set. It’s been almost two weeks of “all good”, no hammer and the red line has been high but black line continues to stay steady. Had our first hammering sound today. Would that have just been a one off or should I lower the pressure a bit more? You had mentioned I could take it all the way down to 15. Would that help eliminate something like that?
If so, does it matter what faucet I use to drain before lowering the psi on the tank? I used the hose bib where I always check the pressure but I have a faucet right between the main line coming in and the expansion tank in the basement. It’s about 10 feet from the tank and 20 feet from the main water line entering home. Thanks so much for your help.

What fixture was being used when the hammering occurred? Did the noise happen when the fixture was being used or when shut off?

It was the powder room toilet. Before I released some pressure in the expansion tank, it would happen pretty often in some of the toilets and even the hose bibs. Once I did that, it stopped, until today. Has only happened once today. As I mentioned, let some of the pressure out almost two weeks ago. Thanks!

You might have a bad washer in the toilet's fill valve or the angle stop for the toilet.

Both were changed. Could lowering the psi on that expansion tank a bit more help?

Lowering the tank pressure will reducing the capacity of the tank and could make things worse.

Thanks but two other plumbers on this blog do not agree with that. I was told I could go all the way down to 15 psi if needed. No5 sur3 what advice to take but lowering the psi two weeks ago really helped!

The manufacturers of expansion tanks state to match the air charge to the static water pressure. Matching the static pressure will keep the diaphragm in a centered position for the majority of time. By having less air charge, the static pressure will push the diaphragm towards the captive air side, lessening the capacity of the tank and can cause premature failure of the diaphragm.

(Amtrol): [www.amtrol.com]
(Watts): [www.youtube.com]
(American Water Heater): [www.americanwaterheater.com]
(whirlpool): [www.whirlpoolwaterheaters.com]



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