Cyclones are amongst the commonest of pollution prevention devices. They work by forcing the effluent flow to take a spiral path and thus make use of the so-called centrifugal force on the particles. Particles with sufficient inertia are thrown outwards and downwards as the gas flow deviates from a straight line. The heavier the particle the greater the tendency to be thrown out of the air stream.

Larger particles are collected on the walls of the cyclone after being thrown outwards into an area close to the walls where the air velocity is essentially zero.