What is Screw Pump & How Does it Works?
A Screw Pump is a positive displacement pump that uses one or more screws to carry fluid solids or liquids along the axis of the screw(s). A screw pump can provide high flow rates even for viscous liquids, which makes them ideal for fuel transfer, elevators, and similar industrial uses. Pumps with a single screw, or Archimedean screw pump, are commonly used for simple water conveyance, including sewage inlet pumps, drainage pumps, stormwater pumps, and wastewater pumps for the industrial sector. Screw pumps are the standard solution for most industrial vacuum processes. Food processing industries commonly use oil-free screw pumps to prevent contaminating pump oil with water or debris during drying, packaging, and freeze-drying. Also, screw pumps are used in large coating operations like architectural glass coaters as roughing pumps for high vacuum pumps. Additionally, screw pumps are the best option for regenerating large cryopumps.
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What Is Screw Pump?
A screw pump, also called a water screw, is a positive displacement pump that utilizes one or more screws in order to transfer liquids or fluid solids along the screw(s) axis. The Archimedes' screw pump is a simple pump consisting of a single screw rotating in a cylindrical cavity, moving the material along the spindle. In many low-technology applications such as irrigation systems and agricultural machinery for moving grain and other solids, this ancient construction is still employed.
Working Principle of a Screw Pump
The screw pump is a type of positive displacement pump. As a result, the liquid is consistently displaced from the space it occupies. In order to drive the screw pump, two counter-rotating screws are used. In this case, the rotating screws are set in such a way as to rotate toward each other.
The driver screw is powered by an electric motor as soon as the screw pump starts working. It is connected to a driving shaft.
During the rotation of the driver screw, the driven screw also rotates with it due to the meshing between these screws. At the inlet section, a slight vacuum begins to develop due to the movement of these screws. As a result of this vacuum, fluid is drawn into the pump from the inlet valve. Upon entering the pump, fluid is trapped between the gap of the "screws." As the screw rotates, this trapped fluid moves as well. Screw movement causes the trapped fluid volume to decrease, as well as the fluid pressure to increase.
As the fluid pressure increases to the desired pressure, it is discharged from the outlet valve and transferred to the destination.
When oil or other viscous liquids are pumped through screw pumps, the screw's surface is lubricated, so that little or no space remains between the screws as the liquid pumps.
On the other hand, when gas/water mixtures, water, or other types of light liquids are pumped, the components cannot come into contact with one another. As a consequence, the parts wear out more rapidly. Therefore, a three-screw pump (in which one screw drives the other two without a gear) is not recommended for water supply or multiphase operation.
Components of a Screw Pump
The major components of a screw pump are as follows:
- Driver Screw
- Driven Screw
- Driving Shaft
- Timing Gear
- Inlet and Outlet Ports
- Pressure Relief Valve
Function of a Screw Pump
Screw pumps are capable of generating pressures of 10-3 mbar. These pumps operate at pressures between 103 and 10-2 mbar. Pumping speeds of 60 - 1200 m3/h are available in various sizes. Placing a roots blower on top of the pump increases pumping speed in the vacuum range below 10 - 50 mbar. There are combinations available for pumping up to 9000 m3/h, often in a single housing.
Screw pumps feature the highest flow rate among any type of positive displacement pump, making them an excellent choice for hard-to-move fluids that need to be moved as rapidly as possible, such as fuels, oils, and other high viscosity liquids in oil and gas applications. Two-phase liquid and gas mixtures can also be handled with screw pumps. However, aside from single screw pumps, they are not proper for moving clean liquids at steady rates. In addition, screw pumps are often complex, requiring more maintenance and requiring shorter equipment than simpler pumps.
Usage of Screw Pumps
Screw pumps are perfect for fuel transfer, elevators, and similar industrial uses due to their capacity to provide high flow rates even for viscous liquids. A single screw pump, or Archimedean screw pump, is used for simple water conveyance, such as sewage inlet pumps, storm water pumps, drainage pumps, and industrial waste water pumps.
Common Applications of Screw Pumps
A screw pump is commonly used in the following applications:
- The supply of oil to large machines is handled by screw pumps in numerous lubrication and hydraulic machines.
- They can pump heavy oils more efficiently. Even higher viscosity and higher flow rate liquids can be pumped through them.
- Gas and liquid can be pumped at the same time through these pumps. This is why they can be found in many pumping industries.
- Other industries that use this pump include oil and gas, mining, and manufacturing.
- They are used in the ceramics, chemical, paint, food, and paper industries.
Advantages of Screw Pumps
Screw pumps have the following advantages:
Compared to centrifugal pumps, screw pumps have many advantages. They pump liquids in an axial direction without turbulence. This means no bubbles are created when viscous liquids are pumped.
- The pumps are easy to maintain.
- They require very little maintenance.
- Screw pumps are suitable for all fluids.
- They are capable of running dry.
- They are compact in design.
- There is little pulsation.
- The pump produces a steady flow of fluid without pulsating.
- There is little noise generated.
- They can produce high volumetric efficiency.
- They have high reliability.
- They are self-priming.
- They have high durability.
- They can handle dust and water vapors well.
- They pump fluid at very high speeds.
- Screw pumps do not pump the contamination.
- They rotate without friction.
- They are highly efficient.
- Screw pumps are also capable of pumping highly viscous liquids without sacrificing flow.
Disadvantages of Screw Pumps
Even though screw pumps offer many advantages, there are some drawbacks as well, such as:
- Installation costs are high for small industries.
- To transfer light gases, this pump requires a gas ballast.
- Without a gas ballast, it has a low pumping speed and a lower ultimate pressure for light gases.
FAQ about Screw Pumps
- What Is a Screw Pump?
Screw pumps are famous examples of positive displacement pumps. They are also called water screw pumps. Screw pumps move fluids or water along the screw's axis using one or more screws.
- What Are Screw Pumps Used for?
Most industrial vacuum processes use screw pumps as the standard solution. The food processing industry tends to use oil-free screw pumps in food drying, packaging, and freeze-drying to avoid contaminating pump oil with water or debris from the process. Screw pumps are used as roughing pumps for high vacuum pumps in large coating operations, such as architectural glass coaters. Furthermore, screw pumps are the best choice for regenerating larger cryopumps.