Short Answer:

A screw pump is a type of positive displacement pump that uses one or more screws to move fluids along the screw axis. The fluid enters the pump at one end and is pushed through the spaces between the rotating screws and the casing toward the discharge side. Screw pumps are mainly used to handle viscous fluids smoothly and continuously without pulsation.

They are highly efficient, quiet, and capable of handling both low and high viscosity fluids. These pumps are commonly used in lubrication systems, fuel transfer systems, hydraulic machinery, and chemical industries where a steady and non-pulsating flow is needed.

Detailed Explanation :

Screw Pump

A screw pump is a type of rotary positive displacement pump that moves fluid by using one or several screw-shaped rotors. The screw or screws rotate inside a tightly fitting casing, trapping fluid between the threads and the casing and pushing it steadily along the axis of rotation. This design ensures a smooth and continuous flow without pulsation, which makes screw pumps suitable for transferring viscous or sensitive liquids.

The screw pump operates on the principle of axial flow. As the screws rotate, the fluid is trapped in the cavities formed between the screw threads and the pump casing. The continuous rotation moves these cavities toward the discharge end, forcing the fluid to flow in a smooth, non-pulsating manner. This mechanism is similar to how a screw moves forward when turned into a material, continuously displacing fluid along its path.

Screw pumps can have one, two, or three screws, depending on their design and purpose. Each type has its own working characteristics and is chosen according to the nature of the fluid and the required pressure or flow rate.

Types of Screw Pump

Single Screw Pump (Progressive Cavity Pump):
In this type, a single screw (called the rotor) rotates inside a double-threaded rubber or elastomer stator. As the rotor turns, cavities are formed between the rotor and stator, which move the fluid along the length of the pump. This pump is commonly used for high-viscosity or slurry-type fluids like sludge, food pastes, and oil.
Twin Screw Pump:
This type uses two intermeshing screws that rotate in opposite directions. The fluid is trapped between the screw threads and is carried from the suction to the discharge side. Twin screw pumps are self-priming and handle a wide range of viscosities. They are used in industries such as food processing, oil, and chemicals because they can handle fragile or shear-sensitive liquids gently.
Triple Screw Pump:
This type consists of three screws — one driving screw (main rotor) and two driven screws (idler rotors). The screws mesh precisely, creating sealed chambers that carry the fluid axially. Triple screw pumps are often used for lubricating oils and hydraulic systems because of their smooth and quiet operation.

Construction of Screw Pump

A typical screw pump consists of:

Casing: Houses the screws and provides a tight sealing path for fluid movement.
Screws/Rotors: Helically shaped rotating parts that trap and move the fluid.
Shafts and Bearings: Support the screws and maintain alignment during rotation.
Inlet and Outlet Ports: Allow fluid entry and discharge.

The screws are usually made from strong materials such as steel or stainless steel to handle high pressure and resist wear from viscous or corrosive fluids.

Working of Screw Pump

Suction Phase: The fluid enters the pump through the inlet side as the screw rotates. The rotation creates low pressure that draws the fluid inside.
Trapping Phase: The fluid gets trapped between the screw threads and the casing in small cavities.
Discharge Phase: As the screw continues rotating, these cavities move forward, carrying the fluid toward the outlet. The fluid is then discharged under pressure without pulsation.

Because of this continuous and steady flow, screw pumps are excellent for systems requiring consistent delivery and low vibration.

Advantages of Screw Pump

Provides steady and non-pulsating flow.
Can handle viscous, abrasive, or multiphase fluids easily.
Self-priming and capable of operating at high suction lift.
Quiet and smooth operation, ideal for lubrication and hydraulic systems.
High volumetric efficiency and long service life due to simple design.

Applications of Screw Pump

Fuel and lubrication oil systems in engines and turbines.
Hydraulic power units.
Food and chemical industries for transferring thick or delicate liquids.
Marine and ship applications for fuel and bilge pumping.
Wastewater treatment and sludge handling systems.

Conclusion:

A screw pump is a reliable and efficient type of positive displacement pump that transfers fluid smoothly by using rotating screw elements. Its ability to handle viscous fluids, maintain steady flow, and operate quietly makes it widely useful in industrial, marine, and hydraulic systems. The simple and durable design ensures long service life and low maintenance, making the screw pump an essential component in modern mechanical systems.