I posted this on the Box2D forums as well, but thought I’d at least give it a shot here too.
The project I’m working on allows users to build their own contraptions by cutting out and designing pieces, and then assemble them all together into a machine.
Now, one of the basic machines will be an air pump. I should be able to simulate air pressure moving out of the pump as several small circles, all crowding each other, however, I want a “flap” to open drawing in new air once the air has been pushed out. Here are a few (crappy) images describing the process.



Any ideas or workarounds? Any other libraries out there that can simulate this?
It’s just for a game, so it doesn’t need to be exact, just believable.