Check Valves For Compressed Air How Can I Prevent Air Backflow?

How can i prevent air backflow? - check valves for compressed air

I need to know if there are check valves (or similar) that prevents a return flow of air. So far I've been in a position, the valves, which prevent reflux in the search for water, but what about Air? Knowing that the air is less dense than water taps to verify water does not work for the air (or air) to. I need it for a project. Please also provide links and sources if possible.