Screw Pump

Screw pumps are rotary, positive displacement pumps that use one or more screws to transfer fluids along an axis.  An example of a screw pump is the Archimedes screw pump that is still used in the irrigation and agricultural industry.  Screw pumps are very good for handeling solids and debris.  The method of pumping is such that it will not tighten the emulsion by shearing it such as a centrifugal pump does.  Fluid is transferred through successive contact between the housing and the screw flights from one thread to the next.

These are lower speed pumps than a centrifugal pump and typically operate between 200 and 1,000 RPM.  There are many variations in the design of the screw pump.  The primary differences consist of the number of screws, pitch of the screws and the general direction of fluid flow.  A progressive cavity pumps is a single screw pumps with a stationary screw and a screw that moves fluid through the pump.

Due to their design wear is typically a problem If the pump is run dry or if the shaft becomes misaligned, pump failure can and will occur.  Unlike centrifugal pumps, a screw pump will continue pumping as long as the motor can spin.  Because of this, it is very important to protect the pump due to low flow or no flow.

Screw Pump Types

Screw pumps are positive displacement pumps that use rotating screws to move fluid along the screw axis.  There are several types of screw pumps, each with its own characteristics and applications.  These pump types offer various advantages, including smooth and pulsation-free flow, self-priming capabilities, and the ability to handle different types of fluids.  The specific type of screw pump chosen depends on the characteristics of the fluid being pumped and the requirements of the application.  Here are three common types:

Single Screw Pump (Progressive Cavity Pump)  -  Consists of a single helical rotor (screw) that rotates eccentrically within a stator.  As the rotor turns, cavities are formed between the rotor and stator, trapping and pushing the fluid along the axis.
Twin Screw Pump  -  Involves two intermeshing screws (rotors) that rotate within a casing.  Fluid is moved axially as the screws rotate, creating cavities between the screws and the casing.
Three Screw Pump  -  Comprises three screws, one driving screw and two idler screws, rotating within a casing.  Fluid is displaced axially by the intermeshing screws, creating sealed chambers that move the fluid along the screw axis.

 

Screw Pump Advantages and Disadvantages
Advantages	Disadvantages
Screw pumps are positive displacement pumps, providing a fixed and predictable flow rate, independent of discharge pressure. Well-suited for handling high viscosity fluids, making them effective in applications involving thick or sticky substances. Many screw pumps are self-priming, capable of evacuating air from the suction line and starting without external priming. Screw pumps generate a smooth and pulsation-free flow, making them suitable for applications where a consistent flow is critical. The pumping action is relatively gentle, making screw pumps suitable for shear sensitive fluids and delicate materials. Can handle a wide range of fluids, including those with suspended solids, abrasive materials, and corrosive chemicals. Generally have a low Net Positive Suction Head (NPSH) requirement, making them suitable for applications with challenging suction conditions. Screw pumps can achieve high efficiency levels, especially in applications with high-viscosity fluids. Can be operated at variable speeds to adjust the flow rate according to the process requirements. The pumping action tends to produce lower noise levels compared to some other types of pumps. Often built with robust materials, making them suitable for handling demanding applications in various industries.	Some screw pumps may be sensitive to abrasive materials, leading to wear and reduced efficiency over time. The design of screw pumps can be complex, and maintenance or repair might require specialized knowledge and skills. Initial purchase and installation costs can be higher compared to some other pump types. Screw pumps may have limitations in handling extremely high or low temperatures, depending on the materials used in their construction. Seals may require regular maintenance, and failure to do so can lead to leaks and reduced pump performance. While screw pumps can handle some solids, their ability to handle large volumes of solids may be limited compared to certain other pump types. Some screw pumps may be sensitive to the presence of vapors, affecting their performance. Depending on the application, screw pumps can be larger and heavier than alternative pump types.

 

Screw Pump Characteristics

Screw pumps exhibit several characteristics that make them suitable for various applications.  Understanding these characteristics is needed for selecting the right type of screw pump for a specific application.  Different designs, such as single screw pumps, twin screw pumps, and three-screw pumps, may exhibit variations in performance and suitability for different fluid types and operating conditions.

Positive Displacement  -  Screw pumps are positive displacement pumps, meaning they displace a fixed volume of fluid with each revolution of the screw(s).  This characteristic makes them suitable for applications requiring a consistent and pulsation-free flow.
Viscosity Handling   -  Screw pumps excel at handling viscous fluids and can effectively pump liquids with a wide range of viscosities.  They are particularly well-suited for applications involving thick or sticky substances.
Self-Priming  -  Screw pumps often have self-priming capabilities, allowing them to evacuate air from the suction line and start pumping without the need for external priming.
Gentle Fluid Handling  -  The pumping action of screw pumps is relatively gentle, making them suitable for handling shear-sensitive fluids or delicate materials.
Continuous Flow  -  Screw pumps provide a continuous and uniform flow, which is advantageous in processes that require a steady fluid supply.
High Efficiency  -  Screw pumps can achieve high efficiency levels, especially in applications with high viscosity fluids, due to their positive displacement design.
Versatility  -  Screw pumps are versatile and can handle a wide range of fluids, including liquids with suspended solids, abrasive materials, and corrosive chemicals.
Low NPSH Requirement  -  They often have a low Net Positive Suction Head (NPSH) requirement, which is beneficial in applications where suction conditions are challenging.
Variable Speed Operation  -  Screw pumps can be operated at variable speeds to adjust the flow rate according to the process requirements.
Low Pulsation  -  Screw pumps generate low pulsation and vibration, contributing to a smoother flow and reduced stress on system components.
Robust Construction  -  Screw pumps are often built with robust materials, making them suitable for handling demanding applications in various industries.
Low Noise Level  -  The pumping action of screw pumps tends to produce lower noise levels compared to some other types of pumps, contributing to a quieter working environment.

Screw Pump Applications

Screw pumps find applications in various industries due to their ability to handle different types of fluids, including viscous and abrasive materials.  The versatility of screw pumps makes them suitable for a wide range of applications where the pumping of viscous, abrasive, or delicate fluids is required.  The choice of a specific type of screw pump depends on factors such as the nature of the fluid, flow rate requirements, and the operating conditions of the application.  Some common applications of screw pumps include:

Oil and Gas Industry  -  Screw pumps are used for the transfer of crude oil, refined products, and various hydrocarbons.  They are employed in drilling mud systems for pumping drilling fluids.
Chemical Industry  -  Screw pumps are suitable for handling a wide range of chemicals, including corrosive and abrasive substances.  They are used for transferring chemicals in the production of pharmaceuticals, petrochemicals, and specialty chemicals.
Wastewater Treatment  -  Progressive cavity screw pumps are used in wastewater treatment plants for handling sludge and other viscous fluids.
Food and Beverage Industry  -  Screw pumps are employed for transferring various food products, such as syrups, sauces, and viscous liquids.  They are used in the production of dairy products, chocolate, and other food items.
Marine Applications  -  Screw pumps are used on ships for various purposes, including lubricating oil transfer, fuel oil transfer, and ballast pumping.
Power Generation  -  Screw pumps are used in power plants for applications such as fuel oil transfer and lubrication systems.
Mining and Mineral Processing  -  Screw pumps can handle abrasive slurries and are used in mining and mineral processing for transporting various materials.
Paper and Pulp Industry  -  Screw pumps are used for transferring pulp, paper stock, and other viscous fluids in paper manufacturing processes.
Construction and Cement Industry  -  Screw pumps are used for pumping cement grout, slurry, and other materials in construction applications.
Automotive Industry  -  Screw pumps can be found in automotive applications, such as lubrication systems in engines and transmissions.
Agriculture  -  Screw pumps are used in agricultural applications for irrigation and transferring fertilizers.
Water Treatment  -  Screw pumps can be used for pumping water in various water treatment processes.