Learn - Dec. 07, 2021
Screw pumps are rotary positive displacement pumps that can have one or more screws to convey high or low viscosity fluids along the shaft. A classic example of screw pumps is the Archimedes progressive cavity pump, which is still used in irrigation and agricultural applications.
Although progressive cavity pumps can be referred to as single screw pumps, typically, screw pumps have two or more intermeshing screws rotating axially clockwise or counterclockwise. Each screw thread is matched to carry a specific volume of fluid. Like a gear pump, screw pumps may include a fixed screw with one or more rotating screws. Fluid is transferred from one thread to the other through continuous contact between the housing and the threads. The geometry can be varied. Screw pumps provide a specific volume in each cycle and are reliable in metering applications.
Screw Pump
The geometry and drive speed of a single or multiple screws will influence the required pumping action. The capacity of a screw pump can be calculated according to the following formula.
Screw surface dimensions
Rotor speed, as each revolution transfers a specific volume
In applications where multiple rotors are used, the load is distributed between multiple rotating screws. When two or more rotors are used, the housing acts as a stator. Depending on the needs of the application, timed or untimed rotors can be selected. Untimed rotors are simpler to design.
The screw pump combines many of the advantages of other pumping solutions: for example, like the centrifugal pump, it has no pressure or suction valves, while like the piston pump, the eccentric screw pump also has an excellent pumping speed. The flow rate is constant and velocity-dependent. Like a gear or screw pump, it handles pumped materials with high viscosity, high particle size, fibers, and inhomogeneous or abrasive materials.
Spraying particularly heavy materials such as gypsum or filler can be a difficult task. The great advantage of screw pumps is that high working speeds and high-quality surface results can be achieved with the minimal physical effort required for machine processing. Conversely, the quality of your work is not reduced and, in addition, you can plaster, fill, coat, or reinforce surfaces much faster. The more time and material savings involved in more surface areas, the more obvious it is.
The combination of factors relating to driving speed, flow rate and the characteristics of the fluid being transferred may affect the flow rate and volume supplied through each chamber. In water and wastewater treatment applications, less viscous solutions require a lower power drive than untreated sewage, residual sludge, or thickened slurry, which may require a higher power motor. The viscosity of the fluid being transferred and the lift force required may affect the speed and power required. Signs of pump failure include reduced flow rates or increased noise. The efficiency of a screw pump requires that each rotor rotates at a rate that allows each chamber to be completely filled to full capacity.
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