Pressure drop

Pressure drop is defined as the difference in total pressure between two points of a fluid carrying network. A pressure drop occurs when frictional forces, caused by the resistance to flow, act on a fluid as it flows through the tube. Pressure drop increases proportionally to the frictional shear forces within the piping network.
There are a number of factors that impact on the degree to which pressure drop occurs in a piping system, including the following:
The nature of the product being pumped, including its density, heat capacity, temperature, viscosity, and the velocity at which it is moving.
Mechanical components in the piping system, including valves, flow meters, adaptors, and couplings. All of these remove energy from the piping system, contributing to pressure drop.
Changes in the elevation of the piping. If the starting elevation of a pipe is lower than its end elevation, the rise in elevation will cause pressure drop as the fluid moves through the pipe. Conversely, if the starting elevation is higher than the end elevation, there will be a pressure gain as the fluid moves through the pipe.

View More On Wikipedia.org