How is flow resistance formed?

　　The flow resistance of liquid in the tube can be divided into two types: frictional resistance and local resistance.

　　1) Frictional resistance: As the liquid runs in the tube, the friction between the liquid layers and between the liquid and the wall forms frictional resistance.

　　2) Local resistance: The resistance caused by the significant deformation of the liquid flow and the collision between the liquid particles due to local obstructions (such as valves, diffusers, etc.) when the liquid flows.