Is someone going to explain the difference between turning the case or the screw?<br><br>In this case, it seems to me the push/pull dichotomy is meaningless.,(reply>), It is a spiral staircase.  When the screw turns,  it is like the stair case spins while people behind you hold you in the same position.  <br>When the casing spins, the people behind you are being pushed forward, they push you up the staircase.  <br><br>Hypothetically,  only the bottom of the casing where the impellers are, has to spin, the rest can be stationary.