The pressure of the fluid at 1 is equal to the pressure at 2. The pressure of the fluid at 1 is equal to the pressure at 3. In the hydraulic systems the flow variable is the effort variable like the velocity in mechanical systems. The relation between the velocity and the flow is that velocity is flow divided by area. If you look at the areas of the figure, you can see that the area in pipe 1 is smaller than in 2 so the fluid will go faster through 1.
Pressure is the effort variable like the force in mechanical systems.