No air is pumped down. The diagram shows "Strom" going down. In German Strom means energy or in this case electricity. Remember air is quite compressible but water is not.
Strom does not mean Energy. It means stream, as in a stream of water, which could be a river, or as in a stream of electrons, which would be electricity. Strom most often refers to Elektronenstrom.
In English energy is a loose synonym of current. My point was that in this case Strom means electricity which you agree with so I'm not sure why you are arguing about semantics.
