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Pipe equivalent length in pneumatic transport

Pipe equivalent length for calculation of pressure drop in conveying pipes

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Section summary
1. Definition
2. Calculation of the pipe equivalent length - shortcut
3. Calculation of the pipe equivalent length - details

1. Definition - What does equivalent length of pipe mean

Several methods to calculate the pressure drop expected in a pneumatic conveying pipe and design it is using the notion of equivalent pipe length. This notion is actually quite convenient to simplify the calculation of pressure drop. It converts the singularities of the pipe layout (vertical sections, bends, valves...etc...) into an equivalent length of straight horizontal pipe which is representing the same pressure drop as the singularity. This page is explaining different ways to calculate the pipe equivalent length.

2. Calculation of pipe equivalent length - simplified method

A very simple way to calculate the equivalent length is to count on the pipe layout the length of horizontal pipe, vertical pipes and the number of bends.

The pipe equivalent length can be estimated in this shortcut method by Le = Lh+2*Lv+5*NB

With :

- Le = equivalent length of the pipe (m)
- Lh = length of horizontal pipe in the whole pipe layout (m)
- Lv = length of vertical pipe in the whole pipe layout (m)
- NB = number of bends

Do not use this method for detail design. But it can be useful for a pre-project or quite troubleshooting on a production line.

The method above assimilates any 90 degrees bends to a pipe length of 5 m. Note that Rhodes in Principles of Powder Technology recommends a value of 7.5 m for the equivalent length of a pipe bend.

3. Equivalent length of pipe fittings - detailed method

To get more precision, it is required to consider pipe singularities according to their type. Some recommendations are given by Agarwal [1] in an article published in 2005. It allows to estimate the pressure loss from fittings.

Valves and fittings Recommended equivalent length
Short radius 90 °bends
12 m
Long radius 90 °bends 6 m
Diverter valve 45 ° 6 m
Diverter valve 30 ° 3 m
Rubber flexible hose 5 times the pipe length
Bends less than 90 ° 12*degree of bends / 90
Special bends like Hammertek or Gamma bends > 12 m
Recommended 12*1.1 to 12*1.2

[1] Theory and design of dilute phase pneumatic conveying systems, Agarwal, Powder Handling and Processing, 2005