The role of pipe bends in a piping system is pressure loss due to flowing velocity head. The equation is as follows:

Delta P = K(V2/2g)

Where:

Delta P = the pressure drop for the flowing velocity

K = Velocity head loss factor

V = Flowing velocity through the pipe bend

g = Gravitational constant

Typical K values:

0.15 for a long radius elbow

0.25 for a short radius elbow.