Board Thread:Questions and Answers/@comment-68.52.222.43-20130201174431/@comment-6024139-20130202000628

You need a valid destination for the output side if you're using pneumatic tubes (chest or machine). If no tubes are used it will throw items on the ground.

The redstone signal has to either hit one of the sides or a red alloy wire has to be placed on the filter in order for it to work.

If you still experience problems, post a picture of your setup and we'll take it from there.