In your particular example, the air in the tube would be at slightly higher pressure than ambient, and because it doesn't have much surface tension (unlike gaso

In your particular example, the air in the tube would be at slightly higher pressure than ambient, and because it doesn't have much surface tension (unlike gasoline) would slightly leak out of the hole on the side as well. In normal conditions fluid has lower pressure if: (a) it was flowing and is now moving faster because of a geometric constriction (b) it is being sucked (i.e. being pulled into a lower pressure region than ambient) Moving fluid has higher pressure if: (c) it was flowing but isn't flowing as fast due to a geometric expansion (d) it was pushed (i.e. coming from a higher pressure area than ambient) Note that in the case of a fan in a tube, the fluid has lower pressure than ambient behind the fan, and higher pressure than ambient after the fan.