I was wrong all along, the pressure check valve is in the PUMP, not the FILTER.
Quote from manual :
CHECK VALVE OPERATION
The electric fuel pump outlet contains a one-way check valve to prevent fuel flow back into the tank, and to maintain
fuel supply line pressure (engine warm) when the pump is not operational. It also is used to keep the fuel supply
line full of gasoline when the pump is not operational. After 30 minutes the fuel pressure may drop to 2.5 bar (36
psi), but the liquid gasoline will remain in the fuel supply line between the check valve and fuel injectors. When the
fuel pump is activated, the fuel pressure should immediately (1-2 seconds) rise to specification.