Chapter 2 Pumping
In this section, we introduce two of the main devices used to pump liquids: centrifugal pumps and gear pumps. The centrifugal pumps are general-purpose devices used to move low-viscosity liquids around in a process; gear pumps are used to pump highly-viscous liquids at a controlled flowrate. In order to form synthetic fibers, a viscous liquid must be pumped through a filter bed and then through tiny spinneret holes, and both units will result in high pressure drops along the flow direction of the viscous liquids. Finally, the flowrate must be maintained within close tolerances in order to produce synthetic fibers of uniform diameter. Gear pumps are used to provide such a closely regulated flow of the highly viscous liquid; although gear pumps could also be used to develop the high pressures required to force the material through the filter and the spinneret, it is more common to use screw extruders for this purpose.