An Analysis Of Acceptable Particle Losses In Tubing

By Mark Hallworth

When a sample is taken for either certification or routine monitoring operations, it is not uncommon for the isokinetic sample probe (ISP) to be in a remote location from the particle counter optics. In this situation, the sample is drawn through tubing to the particle counter. When the sample is to be transported any significant distance in the tube from the point of sampling to the point of measurement, some particle losses will occur in the transport tubing. The losses are dependent on tubing type, flow velocity, tubing diameter and distance. Large particles are lost by a combination of gravitational settling to the bottom of the duct and inertial deposition on the walls of the tubing when directional changes occur.

Transportation of particles in tubing between a sample inlet and the optics of particle counters has at many times been at the forefront of discussion regarding the truth of readings. When the validation implications of losses due to various forces are reviewed, the certainty of the result is always in question. So what are these forces, what are the losses, and what are the acceptable results? This paper addresses these issues to allow for a better understanding of the problem.