This past winter I replaced my HWH and Expansion tank (both were bad). However when the HWH heated up to the Medium set point the relief valve started spitting water. Basically it was doing its job. I went over to the Regulator back flow valve and turned it down a lot. That seemed to stop the HWH from spitting. But now that summer is here the water pressure doesn't even work the lawn sprinklers properly. I have roughly 42 psi at the hose bib. It was around the same when I tested the HWH with the hot water running out of a different sink. The new Expansion tank was factory set at 40 psi with a max of 150. My HWH is a 50gallon capacity and the regulator back flow valve can range from 25-75 depending on set point.

My question is this. If I were to boost the regulator up to 60 psi would I also need to set the Expansion tank at 60 psi? Do they need to be equal or does one need to be greater than the other?

An you know why I am asking