Equivalent Pipe Length Method - Calculating Pressure Loss in Piping Systems

Calculating pressure loss in piping systems with the Equivalent Pipe Length Method

An efficient and simple way to calculate the pressure loss in a piping system is the "Equivalent Pipe Length Method".

1. Make a Diagram of the Piping System

Make a diagram where the system is divided into sections with only one size of pipe and one flow rate in each section. Number the pipe sections.

In the very simply circulating system used in this example, the first pipe section goes from the pump, splits into the two sections - two and four. Section two and four merges back to pipe three that goes back to the pump.

2. Make a calculation table

Make a table where the pressure loss in each sections can be calculated. Add all sections as shown below:

An excel template with the table can be found here:

• Equivalent Pipe Length Method - Excel Template

Note! The flow and pressure units must be adjusted to the data available for your piping system.

3. Add Pipe Size and Pressure Loss to each Sections

Add pipe size in each section. Use tabulated data (or a nomographs). This example is based on PVC pipes schedule 40

• PVC Pipes - Friction Loss and Flow Velocity - Schedule 40 - Water flow in PVC and CPVC pipes Schedule 40 - friction loss and flow velocities at dimensions from 1/2 inch to 16 inches

to determine size. For thermoplastic pipes velocites above 5 ft/sec should be avoided. Add the pressure (head) loss for the actual flow in each pipe section.

The pressure loss may alternatively be calculated with the Hazen-Williams Equation or the Darcy-Weisbach Formula.

• Pressure loss for other types of pipes can be found here.

4. Add Equivalent Length of all Valves, Fittings and Straight Pipes

Add the equivalent length of all valves, fittings and straight pipes in the sections.

• PVC - Equivalent Length Friction Loss in Fittings - Minor loss for PVC and CPVC fittings in equivalent length of straight pipe
• Other data

5. Summarize the Pressure Loss in each Section

Calculate and summarize the pressure loss in each section.

6. Summarize the Pressure Loss in all Paths

Finally, add up the pressure loss in all sections that form unique paths. In the example above there are two unique paths - one is section 1 - 2 - 3, the other is section 1 - 4 - 3.

Extra columns is necessary and should be added in more complicated systems.

The highest pressure loss determines the pump head.

7. Add Balancing Valves

Add valves where it is necessary to balance the system. In the example above a balancing valve is added in section four.

Note! The Equivalent Pipe Length Method can be adapted to most piping systems - even supply systems, gravity systems and similar.

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