Most pumps that produce their own fuel pressure to the injector(s) dont really require a check valve in it. the reason they have one is to make our lives easer when trying to start them up. with a check valve ,,there is fuel from tank to injector creating faster start ups unless there is a leak in the fuel line(s).
For the injector pumps that dont produce their own pressure they have a electric/ manual fuel pump and dont require a check valve because once u turn on the fuel pump switch it pressureizes the fuel system and u have fuel right to the pump and sometimes it will totally bleed all the air out of the system without cracking a fuel line.. most companies include a check valve just to make the start up faster.
I think most of us has heard a old dodge try to start
, they would crank and crank for what seemed forever before they ran,lol. the fuel drained beack to the tank when the car was parked for any lengthy time,( over 1-2 hours
)
Derek