Was trying to think outside the box a bit. You can't inflate a balloon with a filter, but you can with a good set of lungs. I guess the function of the lung is a filter, but some of the mechanics could be explained as similar to that of a pump.
Ooooh!!!! The heart.... ? Am I completely off course here? You've got me thinking....
Heart, good work thats right. it actually pumps. The lungs don't pump, they are inflated and deflated by the movement of the diaphragm. But in saying that I can see how we could draw similarities.
Ha!! Got it!! True, the heart is a muscle and pumps under its own force, whereas the lungs need external force to expand and contract. Just as well I'm not a doctor!!