Screw Pumps

A most important class of pump for dealing with highly viscous material is the screw pump.

Designs employing one, two and three screws are in use.

Multiple screw pumps operate as follows:

• The displacement volume is opened at the suction as the counter-rotating screws unmesh.
• Subsequent meshing of the screws produces a displacement volume bounded by the thread roots, the thread flanks, and the pump casing.
• Continued rotation of the screws translate the displacement volume to the pump discharge.
• At the pump discharge the volume is displaced by the meshing of the screw ends.

In single screw pumps, the fluid is sheared in the channel between the screw and the wall. Flow is produced as a result of viscous forces. Pressures achieved with low viscosity materials are negligible.