Varying water pressure

I find that every few months I have to adjust the main pressure valve in our house to bring up the water pressure. I try to keep it between 50 and 60psi. This is fine for my wife and me. It is just 2 of us in the house. Every few months I will notice a loss of pressure. A test will reveal it is down around 40psi and below.

We have a newer home that is at the end of the water supply line in the street. Can I expect the pressure in our home to vary if the pressure from the public water source varies? I have gotten different opinions on this. I don't know how the pressure in our home would not drop if the PWS pressure does. I don't know if I need to install a new valve or expect these fluctations due to the public water source.

IF you can raise the pressure by adjusting the valve, then the valve is defective. It should ALWAYS have the same outlet pressure, regardless of the city's pressure, as long as the incoming pressure is higher than its setting.