Bernoulli tube airflow and pressure demonstration apparatus rvfm ph10635 p this bernoulli tube apparatus clearly demonstrates that the speed of flow increases and pressure decreases in a constricted section p p a 500mm long tube with a 10mm bore is constricted near its centre a short side tube in each of the 3 sections allows the connection of a manometer tube the 3 manometer tubes clearly show that the pressure in the constricted centre section is lower than in the 2 outer sections p