ok ok i understand but ,it is the energy that the pressure exerts at every point of the fluid in a pipe that's why it is pressure energy per unit volume
for a stream line flow of ideal liquid (non-viscous) imcompressible the sum of pressure energy per unit volume kinetic energy per unit volume , potential energy per unit volume remains constant
mathematically
P+1/2roV2+ROGH=constant
consider a fluid flowing in a pipe of various crossections
we...