I was wondering how one works exactly. I kind of understand. I know that it is a restriction in the fuel line, but if it is in between the fuel pump and the fuel rails, i don't understand how that would work. I don't see how it could make pressure in the rails if it's before the rails. But if it sits in between the fuel rails and the gas tank on the return line side, well, then it makes total sense. Could someone please clarify. Thanks.

 

Very basically your fuel pump is what is creating the pressure. It creates more than your fuel rails or injectors need, so the regulator chokes it down to a usable amount.

Like an air compressor may generate 125 PSI, you would use a regulator in line to choke it down to say 35 PSI to spray paint something.