# Water Pipe Sizing Calculation Example – Part-3 – Determining the Permissible Pressure loss

Refer the part-1 and part-2 of this water pipe sizing design calculation series before following this part of the piping system design calculation. In this part we will see how to calculate the maximum permissible pressure drop in the pipe system.

What is pressure loss?

The fluid, while flowing through the piping network, experience frictional resistance due to the velocity of the fluid and the viscosity of the fluid. This frictional resistance reduces the pressure of the fluid. This reduction of the fluid pressure is known as pressure drop or pressure loss of the fluid.

Calculation of permissible pressure drop in a pipe

Maximum permissible pressure drop in a piping system = Total available head /Effective pipe length……Eq.1

In part-2 of this series, we already calculated the effective pipe length for our example and the value of that is 22 meters.

And, from the problem definition, it is clear that available pressure head for our case is 5 meters.

So, from the Eq.1, maximum permissible pressure drop for the piping system for our example = 5/22=0.22 meter of head per meter of pipe run.

In the next part (part-4), we will see how to calculate the hydraulic diameter of the piping network.