Fuel tank vent valve

[JDM_DSM]

Does the blue valve on top of the fuel tank act as a 1 way check valve, or is it just there to prevent fuel going through it in the case of a roll-over?
I noticed tonight that I can blow quite easily through it in both directions. Is that normal? Is there a way to test if it's still working like it should?

 

[manikbastrd]

I could also blow through mine. I believe that it is a filter, to prevent gunk from going into your tank.

 

[JDM_DSM]

Works for me. Thanks.