Hello again, I have no earthly idea what could be going on with the cartridge at your shower faucet or why replacing it solved the problem but only lasted 4 months... that is a very unusual sort of anomaly.
We could a long time trying to sort that issue out and still never come to a conclusion...
It will be most fruitful to focus on the basic physics of water hammer and approach it from that direction and solve the problem on those basics.
The higher the water pressure, the harder it slams a dead head when water flow is suddenly shut off. Lowering the water pressure lowers that potential.
That is why we need to look for a water pressure regulator or fit one and set the pressure lower. 45 psig is a good number, 60 psig is common, but if you are having water hammer issues, we might very well eliminate them at 45 psig.
The bladder in your existing expansion tank might be broken, if thats the case you will have water hammer and other problems... they come with 25 psig of air them, that runs up to the city water pressure of course when in use.
Depress the schraeder valve core on the end of the tank *very briefly, 1/2 a second, if water comes out, you need a new expansion tank... and that would solve the problem in most cases.
water pressure regulator
Look all that over please, we can go from there.
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