AIR JET MILL - EMCO PSI 8 The Pharmaceutical jet mill utilizes compressed air to grinding system which rapidly expands to generate a high speed rotation of material which runs below sonic speed. This creates near sonic particle-on-particle collision, generating increasingly smaller particles. Centrifugal force holds larger particles in the grinding rotation area until they have achieved the desired fine particle size. Centripetal force drags the desired particles towards the static classifier where they are allowed to exit upon achieving the correct particle size.