Single Screw Pump: A Versatile Solution for Viscous Fluid Transfer
In industries where thick, abrasive, or sensitive fluids need to be transported with precision and reliability, the single screw pump—also known as a progressive cavity pump—proves to be a highly effective solution. This positive displacement pump stands out for its ability to handle challenging materials that other pump types struggle with, all while maintaining a smooth, pulsation-free flow.
This article delves into what a single screw pump is, how it works, where it’s used, and what to consider when selecting one.
What is a Single Screw Pump?
A single screw pump is a type of rotary positive displacement pump that moves fluids through the action of a rotor (screw) turning within a stator. The rotor has a helical shape, and as it rotates inside the stator—a rubber-lined or elastomeric sleeve with a double-helix cavity—it forms sealed chambers that progress from the suction side to the discharge side of the pump.
These progressing cavities allow the pump to deliver a continuous, non-pulsating flow of fluid, even with high-viscosity, abrasive, or shear-sensitive materials.
How Does a Single Screw Pump Work?
The basic working principle of a single screw pump (progressive cavity pump) involves:
- Rotor: A metal helical screw (usually chrome-plated or stainless steel) that rotates.
- Stator: An elastic casing with an internal profile that matches the shape of the rotor, typically made of rubber or other elastomers.
- Cavities: As the rotor turns, cavities form between the rotor and stator. These cavities move the fluid from the inlet to the outlet.
This creates a positive displacement action—meaning the fluid is pushed through at a consistent rate regardless of pressure or viscosity, up to a certain limit.
Key Features and Advantages
✅ Handles High Viscosity Fluids
Single screw pumps excel at pumping thick, sticky, or highly viscous materials such as molasses, slurries, pastes, and oils without the need for external priming or heating.
✅ Low Shear Pumping
Ideal for handling shear-sensitive materials (e.g., food products, emulsions, polymers), these pumps minimize product degradation during transfer.
✅ Self-Priming
They can draw fluids from a low or empty tank due to their strong suction capabilities (typically up to 9 meters of vertical suction lift).
✅ Pulsation-Free Flow
Unlike piston or diaphragm pumps, screw pumps provide a steady, pulse-free output, making them ideal for dosing or metering applications.
✅ Reversible Operation
Most single screw pumps can operate in both directions, which is useful for cleaning or system design flexibility.
✅ Tolerant to Solids and Abrasives
These pumps can handle fluids with suspended solids or abrasive particles (e.g., wastewater, drilling mud) without clogging.
Common Applications of Single Screw Pumps
Because of their versatility, single screw pumps are used in a wide variety of industries:
1. Food and Beverage
- Chocolate, honey, molasses, sauces, yogurt
- CIP (Clean-in-Place) and SIP (Sterilize-in-Place) systems
2. Wastewater Treatment
- Sludge and slurry pumping
- Dewatered cake transfer
- Chemical dosing
3. Oil and Gas
- Crude oil transfer
- Drilling mud
- Tank unloading
4. Chemical Industry
- Acidic or alkaline solutions
- Resins, polymers, solvents
5. Cosmetics and Pharmaceuticals
- Creams, lotions, gels, toothpaste
- High hygiene applications with sanitary designs
6. Agriculture
- Manure, fertilizer, animal feed paste
Design Variations
Single screw pumps come in several design configurations to suit different applications:
- Close-Coupled vs. Bare Shaft
Close-coupled pumps integrate the motor and pump into one unit, saving space. Bare shaft models are more customizable. - Hopper-Type Screw Pumps
Designed with a hopper feed for very thick, non-flowing products like pastes or doughs. - Sanitary/Hygienic Designs
Made with stainless steel, polished surfaces, and tri-clamp connections, ideal for food, pharma, or cosmetic use. - Multistage Screw Pumps
Feature longer rotors for higher pressure applications, typically up to 48 bar or more.
Material Considerations
To ensure compatibility with various fluids, single screw pumps are made from different materials:
| Component | Common Materials | Considerations |
| Rotor | Stainless steel, chrome-plated steel | Wear resistance, corrosion resistance |
| Stator | NBR (nitrile rubber), EPDM, FKM (Viton), silicone | Chemical resistance, temperature |
| Housing | Cast iron, stainless steel, plastic (PP, PVDF) | Based on chemical compatibility and hygiene needs |
Limitations of Single Screw Pumps
While versatile, these pumps do have some limitations:
- Wear Over Time: The stator (rubber component) is prone to wear, especially with abrasive fluids.
- Not Ideal for Thin, Low-Viscosity Fluids: The pump relies on a tight seal between rotor and stator, which can struggle with very thin fluids under high pressure.
- Limited Speed: Excessive speed causes overheating and premature wear, so they typically run at low RPMs (~200–500 RPM).
- Pressure Constraints: While multistage versions can handle higher pressures, single-stage pumps have pressure limitations (~6–12 bar).
Maintenance and Servicing
Maintenance requirements are generally low, but regular checks are essential for optimal performance:
- Monitor Stator Wear: As the rotor rotates against the stator, elastomer wear is inevitable.
- Lubrication: Mechanical seals and bearings must be properly lubricated.
- Avoid Dry Running: Running without fluid can cause immediate damage to the stator due to overheating.
Many modern screw pumps come with dry run protection and temperature sensors to prevent this.
Selection Tips: How to Choose the Right Single Screw Pump
When selecting a single screw pump, consider the following parameters:
- Fluid Characteristics: Viscosity, abrasiveness, temperature, and chemical compatibility
- Flow Rate Requirements: Typically ranges from 0.1 to 100 m³/h or more
- Pressure/Head: Number of stages needed to reach desired pressure
- Solids Content: Particle size and concentration
- Installation Footprint: Horizontal or vertical design; space availability
- Hygiene Requirements: Is the pump used in sanitary or CIP/SIP environments?
Always consult with a pump specialist or supplier when dealing with complex or hazardous fluids.
Conclusion
The single screw pump is a workhorse in industrial fluid handling, offering unique capabilities in transferring viscous, abrasive, and delicate fluids. Whether in food processing, wastewater treatment, or chemical manufacturing, its robust design and gentle pumping action make it indispensable.
While it requires careful selection and periodic maintenance, a well-specified and properly operated screw pump can deliver years of reliable service with minimal downtime.
