What is the gas filter on the pressure sensor?
 

In the diagram for the FD there is a gas filter between the UIM and the pressure sensor, is this the same as the check valves that is used for Double Throttle, Purge Control and Pressure Chamber?

See the diagram for reference.

It's what you said. A filter. It's not a check valve, although it's marked so that you don't flip it around and contaminate the sensor.

Dave