Hello- First post here, I can't seem to wrap my head around this concept and how to overcome it. I read here: https://www.physicsforums.com/threads/air-lock-concept.83124/ that air's compressibility is what stops flow, why is this? I also read that a stronger pump (in a vehicle's fuel system, for example) can theoretically overcome vapor lock. What is the tipping point? Does the air bubble need to be compressed to the same pressure as the liquid to keep moving? I am trying to think of an analogy which would help myself understand but not coming up with anything at the moment. Thank you for any insight.