Originally Posted by HarleyBaby

Sorry onehundred 80 , but the valve in the filter, which is the regulator, is always closed, not open . that is until the pressure gets too high, such as low demand. ( maybe letting the engine idle for a period of time). Then the valve opens and lets the fuel return to the tank.Once the valve opens, and enough fuel or pressure is released, the valve automatically closes again. If it were always open, it would never build up pressure. I believe what the problem with aftermarket filteres is this. Once the valve opens when the pressure excedes the set amount it gets stuck open with something. That something being in all of my cases alluminum particles. Every filter that malfunctioned had particles in it. My guess is poor quality control. Also, when the filter is new there is only one way you can blow thru it. Inlet from fuel pump, directly thru to outlet going to engine. No restrictions. Other than injectors being closed. But the other two ports goes to emissions and the other to the tank. If you plugged the outlet going to the engine and blew into it no air would come out of these other two lines. But after failure, you could blow in it with the engine outlet blocked, and air would come out of the tank line. Anyway, not trying to argue about this, only kinow because of my intense involvement with this problem. The valve in the fuel pump is a check valve, and it only keeps the fuel at the pump. It holds no pressure. Hope this clears up how the fuel filter/ pressure regulator works.