Well issues

Basic question: Is 28-30 psi enough pressure for a house? It seems fine at all the fixtures. Second, my well pump runs and will not shut off unless I manually shut it off. The pressure tank is at 18 psi; the pressure switch is 20-40, although I've tried altering the switch to different in and out levels a 100 times. The switch is brand new. So my question is, if I can pull nearly 30 psi and the pressure tank fills, why can't I ever get the pump to shut off? I've been working at this for 3 days.

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