What Is a Single Screw Pump?

A single screw pump (also known as a progressive cavity pump or eccentric screw pump) is a positive displacement pump that transfers fluid through the rotation of a single helical rotor within a double-helical elastomeric stator. This design creates sealed cavities that move axially from suction to discharge, delivering steady, pulsation-free flow with minimal shear.

The core working principle involves an eccentric single-headed helical screw (rotor) rotating within a fixed bushing (stator) with a double-headed helical cavity. As the rotor turns via a universal joint drive, it forms continuous sealed chambers that transport medium from inlet to outlet without agitation—making it ideal for shear-sensitive fluids.

Key Technical Specifications

How to Choose Single Screw Pumps: Selection Criteria

Selecting the right single screw pump requires systematic analysis of fluid properties, operating conditions, and economic factors. Improper selection leads to premature wear, clogging, or insufficient performance.

Step 1: Analyze Fluid Characteristics

Fluid properties are the most critical selection factors. Consider these parameters:

• Viscosity: Measure in mPa·s or centipoise. High-viscosity fluids (>10,000 cP) require low-speed operation.
• Abrasiveness: Specify particle type, hardness, shape, and concentration. Abrasive applications need hardened rotors (tool steel, ceramic coating) and wear-resistant stators.
• Corrosiveness: Chemical composition determines material selection—304/316 stainless steel rotors and NBR, EPDM, or Viton stators.
• Temperature: Ranges affect elastomer selection and mechanical seal specifications.

Step 2: Define Operating Parameters

Calculate your process requirements precisely:

• Flow Rate: Define required capacity in m³/h. Remember flow is directly proportional to rotational speed.
• Pressure Requirements: Calculate total discharge pressure (system pressure + static head + friction losses). Each pump stage typically provides 0.6 MPa (87 psi) pressure capability.
• Speed Selection: For viscous or abrasive fluids, reduce operating speed to 100-300 RPM to minimize wear. Clean, low-viscosity fluids allow higher speeds up to 600 RPM.

Step 3: Material Selection Guide

Step 4: Inlet and Drive Configuration

Ensure proper inlet conditions to prevent cavitation: provide positive suction head for high-viscosity fluids, and consider these drive options:

• V-Belt Drive: Cost-effective, allows speed adjustment via pulley changes
• Geared Motor with Coupling: Compact, fixed speed ratio
• VFD (Variable Frequency Drive): Recommended for process control—enables flow adjustment from 10% to 100% capacity

FAQ About Single Screw Pumps

Why Is My Single Screw Pump Not Drawing Liquid?

Follow this troubleshooting sequence from external to internal factors:

1. Check suction line: Inspect connections and flanges for air leaks—even tiny gaps destroy vacuum. Verify inlet valves are fully open and strainers are clean.
2. Verify liquid level: Ensure suction inlet is fully submerged. For high-viscosity fluids, consider pre-heating to improve flowability.
3. Inspect pump components: Confirm correct rotation direction (match arrow indicator). Check stator wear—worn stators lose sealing capability and self-priming ability.
4. Verify operating conditions: Ensure speed is sufficient to generate adequate suction force.

Can Single Screw Pumps Handle Water?

Single screw pumps are NOT cost-effective for water applications. When designed for viscous fluids and run on water:

• Slip increases significantly at slow speeds
• Volumetric efficiency drops below acceptable levels
• Motors sized for viscous products run inefficiently on water
• Absorbed kW on water exceeds liquid power

For water-like fluids, centrifugal pumps offer better efficiency and lower lifecycle costs.

What Maintenance Is Required?

The stator is the primary wear component requiring periodic replacement. Implement this maintenance schedule:

How Do I Specify Pump Requirements?

When requesting quotations, provide these specifications (note: centrifugal pump data sheets do not apply):

• Fluid properties: viscosity, density, temperature, chemical composition, solids content and particle size
• Operating conditions: required flow rate (m³/h), discharge pressure (bar/MPa), suction conditions
• Material preferences for rotor, stator, and casing
• Sealing type: gland packing or mechanical seal
• Drive configuration and VFD requirements

What Causes Excessive Noise or Vibration?

Common causes and remedies:

• Misalignment: Check coupling alignment between motor and pump
• Loose mounting: Verify pump fixings to baseplate
• Air ingress: Inspect pipework connections for wear
• Internal contact: Check bearings, shaft wear, and casing condition—replace components as required
• Relief valve chatter: Verify set pressure and increase if valve is cycling rapidly

Industry Applications

Single screw pumps serve critical functions across diverse industries due to their ability to handle complex fluids:

• Oil & Gas: Crude oil transfer, drilling mud circulation, heavy fuel oil pumping—handling viscosities up to 200,000 cP
• Food & Beverage: Chocolate, yogurt, honey, sauces—maintaining product integrity through gentle handling
• Pharmaceutical: Precise dosing of creams, gels, and syrups with ±1% accuracy
• Wastewater Treatment: Sludge transfer with solids content up to 60%
• Chemical Processing: Corrosive and abrasive chemical transfer with specialized material configurations
• Mining: Tailings and slurry pumping with high abrasion resistance