filament check valve / return brake

This is a check valve (one way valve) for filament which can be used eg for MMU applications.

Use a ball with 4mm in diameter. You can find one in every 608 bearing.

It is meant to be a concept but it actually works very well.

The screw which holds the ball in place could be replaced by a closed canal for the ball and placing the ball in during printing. This makes it airtight too.

Use higher infill density than me so it props the ball well.