Screw Pumps

A screw pump is a type of positive displacement pump that uses one or more rotating screws (helical rotors) to move fluid or material along the axis of the screw. As the screw rotates within a closely fitting chamber or stator, it creates cavities that trap and then continuously push the fluid from the suction end to the discharge end, providing a steady, pulsation-free flow.

Types of Screw Pumps

Single Screw Pumps (Progressive Cavity Pumps/PCP): Feature a single helical rotor rotating eccentrically within a double helical stator. Most common for viscous, abrasive, or solid-laden fluids.

Twin Screw Pumps: Have two intermeshing screws that rotate in opposite directions, creating cavities that convey the fluid. Used for sensitive, high-viscosity, or multiphase fluids.

Triple Screw Pumps: Three intermeshing screws (one power rotor and two idler rotors), commonly used for lubricating oil in high-pressure applications.

Dry Screw Vacuum Pumps: Specialized screw pumps for creating vacuum in industrial processes, handling gases and vapors without requiring sealing liquids.

Architectural/Archimedes Screw Pumps: Large, open screws typically used for lifting large volumes of water or wastewater at low heads.

Sanitary Screw Pumps: Designed for food, pharmaceutical, and cosmetic industries with high hygiene standards and CIP capability.

Applications in Various Industries

Wastewater Treatment: Pumping raw sewage, sludge, and slurries (especially single screw and Archimedes screw pumps).

Oil & Gas: Transferring crude oil, drilling mud, refined products, and multiphase fluids.

Chemical Industry: Handling viscous chemicals, polymers, paints, and abrasive slurries.

Food & Beverage: Pumping dough, fruit pulp, chocolate, sauces, yogurt, dairy products (sanitary design is crucial).

Pharmaceutical & Cosmetics: Transferring creams, gels, lotions, and pharmaceutical suspensions.

Mining: Pumping abrasive slurries.

Marine: Fuel oil transfer, lubricating oil systems, bilge pumping.

Technology:

Positive Displacement: Delivers a constant volume of fluid per revolution, regardless of discharge pressure (within limits).

Rotor-Stator Geometry: The precise fit and helical design create sealed cavities for fluid transfer. In PCPs, the elastomeric stator deforms to create this seal.

Low Shear Pumping: Gentle handling of sensitive or shear-sensitive fluids (e.g., food products).

Self-Priming: Excellent self-priming capabilities.

Ability to Handle Solids: Especially single screw and Archimedes screw pumps can handle fluids with high solid content.

Dry Running (limited): Some designs can tolerate brief dry running.

Material Selection Considerations

Rotor (Screw):

• Stainless Steel (SUS304, SUS316, Duplex): Common for food, pharmaceutical, and corrosive chemical applications.
• Hardened Tool Steel / Chrome Plated Steel: For abrasive applications to enhance wear resistance.
• Stator (for Progressive Cavity Pumps):
• Elastomers: Natural rubber, Nitrile rubber (NBR), EPDM, Viton, Hypalon, PTFE. Chosen based on chemical compatibility with the pumped fluid, temperature, and abrasive resistance.

Housing/Casing:

• Cast Iron: For general industrial applications, water, and less corrosive fluids.
• Stainless Steel: For food, pharmaceutical, and corrosive chemical applications, or where hygiene is critical.
• Ductile Iron: For higher pressure or more demanding applications than standard cast iron.
• Shaft: High-strength stainless steel or alloy steel.
• Seals: Mechanical seals (common for twin/triple screw pumps) or packed glands (common for PCPs) with materials selected for chemical compatibility, temperature, and pressure.
• Bearings: External bearings, often protected from the pumped fluid, designed for radial and axial loads.