Water Pipe Sizing Calculation Example – Part 1: Overview

This water piping system design calculation example will use the Darcy-Weisbach equation to calculate the pressure loss in a pipe and using that value it will check the appropriateness of the assumed pipe size.

Problem Definition









Fig.1:Water Pipe Sizing Design Calculation Schematic










Refer the above schematics (Fig.1) and observe the following inputs:

Total pipe length=7 meters

Pressure head=5 meters

Number of ball valves=2

Number of Tee bend=1

Also assume that the required flow rate at the pipe end is 0.5 liter/sec.

Find out the appropriate pipe size


Following stepwise procedure needs to be followed for finding out the appropriate pipe size of this water pipe sizing calculation example:

Step-1: Assume the pipe diameter as 20 mm.

Step-2: Determine the Effective Pipe Length

Step-3: Determine the Permissible Pressure Loss

Step-4: Determine Hydraulic Diameter of the pipe

Step-5: Determine the Relative Roughness of the pipe

Step-6: Determine the Reynolds Number

Step-7: Determine the Moody friction factor using Moody diagram

Step-8: Determine the Actual Pressure Drop in the Pipe using Darcy-Weisbach equation and check if it is below the permissible pressure loss as calculated in step-3

In the next part (part-2) of this pipe size calculation series will discuss about calculating effective pipe length.


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