Yeah, I was guessing a pulse dampener also. As to "it shouldn't be there" I had to chuckle. I also agree with that, But it IS on the car and I sure didn't put it there, and it DOES show up on the schematic - Chrysler just chose not to identify it. A critique on the factory manual - they have all sorts of drawings with numbers all over them but NO legend as to what parts the numbers are calling out. Have to read the text to try and get a half way idea as to what is what because they don't reference all of the numbers in any text discussion. Is this a case of German engineering admitting that the thing has relative little value, so while it is there it cannot be tested so please just ignore it?

Also to clarify check valves in both the filter and pump, Volume 2 of 3, Page 14-4 of my 2005 OEM Shop manual at the bottom of the page has:

"Note: A quick loss of pressure usually indicates a defective check valve in the pressure regulator. A slow loss of pressure usually indicates a defective check valve in the fuel pump. These valves are not serviced separately if found defective, the entire component that the valve is part of much be replaced as an assembly."

Since the regulator is part of the filter, it seems that the filter indeed has a check valve.