The advantages and disadvantages of screw pumps
Screw pumps are a unique type of rotary positive displacement pump in which the flow through the pumping elements is truly axial. The liquid is carried between the screw threads on one or more rotors. The liquid is then displaced axially as the screws rotate and mesh. In other types of rotary pumps, the liquid is forced to travel circumferentially, however the screw pump has an axial flow pattern and low internal velocities.
It provides a number of advantages in many applications where liquid agitation or churning is objectionable. Screw pumps are classified as two different types: the single rotor and the multiple rotor. The multiple rotor is further divided into timed and untimed categories. Timed rotors rely on outside means for phasing the mesh of the threads and for supporting the forces acting on the rotors. Untimed rotors rely on precision and accuracy of the screw forms for proper mesh and transmission of rotation.
Advantages
1. Wide range of flows and pressures
2. Wide range of liquids and viscosities
3. Built-in variable capacity
4. High speed capability allowing freedom of driver selection
5. Low internal velocities
6. Self-priming with good suction characteristics
7. High tolerance for entrained air and other gases
8. Minimum churning or foaming
9. Low mechanical vibration, pulsation-free flow, and quiet operation
10. Rugged, compact design — easy to install and maintain
11. High tolerance to contamination in comparison with other rotary pumps
Disadvantages
1. Relatively high cost because of close tolerances and running clearances
2. Performance characteristics sensitive to viscosity change
3. High pressure capability requires long pumping elements
