Pressure drop is defined as the difference in
pressure between two points of a fluid carrying network. Pressure drop occurs when
frictional forces, caused by the resistance to flow, act on a
fluid as it flows through the tube. The main determinants of resistance to fluid flow are fluid
velocity through the pipe and fluid
viscosity. Pressure drop increases proportional to the frictional
shear forces within the piping network. A piping network containing a high relative
roughness rating as well as many pipe fittings and joints, tube convergence, divergence, turns, surface roughness and other physical properties will affect the pressure drop. High flow velocities and / or high fluid viscosities result in a larger pressure drop across a section of pipe or a valve or elbow. Low velocity will result in lower or no pressure drop.