FAQ - Airborne Particles

Question
What is the limit on how much tubing can bend (max. radii) vs. the inner diameter of the tubing?

Answer

The ideal bend radii are:

1. cfm = 4" optimum (2" minimum)
2. cfm = 8" optimum (4" minimum)

The minimum values here are used only if a tight obstacle needs to be overcome. Other impacts such as number of bends will also impact the amount of particle loss in transport tubing. Maximum length of tubing to be used in 2 m for a 1 cfm instrument.

The actual values are based upon a rule of thumb for bend radii used in lean phase particle transit, Bend Radius = 4 x ID tubing used. So you can see that even if we use a 1cfm device with 10mm (3/8") tubing our radius should be no less than 40 mm which is still less than the 2" used as absolute minimums. The rules are not directly translatable as we are looking at very, very lean phase as there is no significant mass loading to the air stream, but it does work very well.

For further information read An Analysis of Acceptable Particle Losses in Tubing or Particle Loss in Transport Tubing.