The suction from skimmer sucks water through the lower turbine into the skimmer and towards the filter causing the turbine to turn, because it is a fixed spindle the top turbine is also turned and it sucks water into the device and pushes it into vacuum hose through the end attached to the vacuum hose. Again, the drawing is how I remember it and is probably lacking some key detail that would make it make immediate sense to all. I can only tell you at this point that it worked great for hundreds of pool cleanings - - until I lost it.