Archimedes Pumps

Category: Adhesives and Dispensing
Post Date: July 20, 2004
Author(s): Douglass Dixon, GDM Product Manager, Universal Instruments

Description
With Archimedes pumps, constant air pressure is applied to a syringe that forces material down a material feed tube. The material comes in contact with the screw, which turns for a set length of time or rotates at a specified speed. The rotation of the screw creates a shearing force on the material, causing it to move down the threads of the screw. As the material reaches the needle hub (the area between the end of the screw and the needle shaft), it encounters resistance to flow due to the restriction in area at the needle shaft. The screw continues to turn, creating pressure high enough to force material through the needle. Any area restriction such as the needle at the output of the auger creates backflow. The amount of backflow is proportional to the pressure drop from the needle hub to the syringe. The flow out of the needle is equal to the pump shear flow minus the backflow. If the needle requires a higher pressure to flow than the screw can deliver, then back pressure is created and material will not f low out of the needle.

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