1. What Is a Three Screw Pump?
A three screw pump (also called a triple screw pump) is a rotary positive displacement pump designed for continuous, pulsation-free transfer of lubricating, non-corrosive liquids. Three intermeshing screws — one driving and two driven — form sealed axial chambers that transport fluid from suction to discharge without turbulence.
Three screw pumps are extensively used in:
- Marine & Shipbuilding
- Metallurgy & Steel
- Petrochemical Industry
- Power Generation
- Mechanical Processing
- Hydraulic Systems
Typical Performance Specifications
| Parameter | Typical Range | Notes |
|---|---|---|
| Flow Rate | 0.5 – 1,200 m³/h | Varies by screw diameter and pitch |
| Discharge Pressure | Up to 25 MPa | Standard units: 1.6 – 4 MPa; high-pressure variants up to 25 MPa |
| Viscosity Range | 1 – 3,000 mm²/s | Best efficiency at 20 – 500 mm²/s |
| Operating Temperature | −20°C to 200°C | Material-dependent; standard seals rated to 120°C |
| Rotational Speed | 960 – 3,600 RPM | Higher speed suits lower viscosity media |
| Volumetric Efficiency | 85 – 98% | Decreases at lower viscosity or higher pressure differential |
2. Three Screw Pump Working Principle
A three screw pump consists of:
- One driving screw (power input shaft)
- Two driven screws (idler rotors, hydraulically balanced)
- Pump casing / liner (precision bored to screw profile)
The three screws are arranged parallel and symmetrically inside the pump casing. When the driving screw rotates, sealed chambers are formed between the screws and the casing wall. The sequence:
- Liquid is drawn into sealed chambers at the suction port.
- Chambers travel axially along the screw axis — no radial pumping action.
- Fluid reaches the discharge side and is expelled at system pressure.
- New sealed chambers continuously form at suction, creating steady flow.
Because fluid moves axially rather than radially, there is no vortex formation, resulting in low pulsation, low noise, and stable flow — key advantages over centrifugal and gear pumps in sensitive systems.
3. Structural Features and Advantages
3.1 Hydraulic Balance Design
The driving screw is hydraulically balanced via opposing pressure areas; the driven screws are kept in position by hydraulic forces rather than mechanical contact. Under rated conditions:
- Screws do not contact each other
- A stable hydrodynamic oil film (typically 5–20 µm thick) forms between screw surfaces
- No metal-to-metal contact occurs — wear is virtually eliminated
3.2 Long Service Life
Three screw pumps regularly achieve 50,000–80,000 hours of continuous operation in marine and industrial lubrication systems when operating within design parameters. Key contributors:
- Oil film lubrication eliminates abrasive wear
- High-precision screw machining (tolerance: ±0.005 mm typical)
- Case-hardened screw surfaces (55–62 HRC typical)
- Proper material pairing (alloy steel driving screw + cast iron or bronze liners)
Note: During startup and shutdown, brief boundary lubrication occurs as the oil film is not yet fully established. Screw surface hardness and material compatibility are critical design considerations for transient load resistance.
4. Applications and Suitable Media
Three screw pumps are optimized for clean, lubricating liquids without abrasive particles. The following table summarizes common media with viscosity references:
| Media | Typical Viscosity (mm²/s @ 40°C) | Suitability |
|---|---|---|
| Mineral Lubricating Oil (ISO VG 32–100) | 28 – 100 | Ideal |
| Synthetic Hydraulic Oil | 15 – 68 | Ideal |
| Light Fuel Oil (Marine DO) | 2 – 6 | Suitable (check NPSH) |
| Heavy Fuel Oil (HFO 380) | 300 – 700 | Suitable with heating; verify model rating |
| Gear Oil / Transmission Fluid | 68 – 460 | Suitable |
| Coal Tar / High-Temperature Asphalt | 500 – 3,000+ | Requires high-viscosity variant; consult engineer |
| Emulsion (Water-Glycol) | 25 – 50 | Suitable; verify material compatibility |
| Fluids with solid particles > 0.1 mm | — | Not recommended — use progressive cavity pump |
5. Three Screw Pump vs. Other Rotary Pump Types
| Criteria | Three Screw Pump | Twin Screw Pump | Gear Pump (External) | Vane Pump |
|---|---|---|---|---|
| Flow Pulsation | Very Low | Low | Low–Medium | Low |
| Noise Level | Very Low (<70 dB typical) | Low | Medium | Low–Medium |
| Multiphase / Mixed Media | No | Yes | No | No |
| Max Pressure | Up to 25 MPa | Up to 4 MPa | Up to 35 MPa | Up to 17 MPa |
| Viscosity Range | 1 – 3,000 mm²/s | 1 – 100,000 mm²/s | 5 – 100,000 mm²/s | 10 – 500 mm²/s |
| Self-Priming | Yes | Yes | Yes | Yes |
| Dry Run Tolerance | No — requires immediate lubrication | Limited | Limited | Limited |
| Typical Service Life | 50,000–80,000 h | 20,000–40,000 h | 15,000–30,000 h | 10,000–20,000 h |
| Maintenance Interval | Low | Medium | Medium | Medium–High |
| Best For | Lube oil, hydraulic, fuel systems | Crude oil, process, multiphase | High-pressure hydraulics | Low-pressure hydraulics |
6. Industry Applications at a Glance
| Industry | Typical Application | Key Requirement |
|---|---|---|
| Marine & Shipbuilding | Main engine lube oil, fuel transfer, cargo heating | Low noise, vibration-resistant, IMO compliant |
| Metallurgy & Steel | Rolling mill lubrication, hydraulic press systems | High pressure, high viscosity capability |
| Petrochemical | Crude pre-heating, tank farm transfer, seal flush | Temperature resistance, chemical compatibility |
| Power Generation | Turbine lubrication, governor oil supply | Ultra-low pulsation, high reliability (24/7) |
| Mechanical Processing | CNC machine tool coolant & lube circuits | Compact size, low noise in workshop environment |
| Hydraulic Systems | Hydraulic power unit (HPU) charge pumps | Stable flow, variable pressure range |
7. Frequently Asked Questions
Q1: How does a three screw pump differ from a twin screw pump?
Three screw pumps use one driving screw and two hydraulically-driven idlers — they excel with clean lubricating oils and can achieve higher operating pressures (up to 25 MPa). Twin screw pumps handle multiphase and mixed media (including gas-entrained or particle-laden fluids) and tolerate dry-run conditions better, making them standard for crude oil and process applications.
Q2: Can three screw pumps handle high-viscosity liquids?
Yes. Three screw pumps operate effectively up to approximately 3,000 mm²/s. For very high-viscosity media (>1,000 mm²/s), heating of the fluid and/or the pump casing is often recommended to maintain stable oil film formation. Consult a pump engineer for media above 1,500 mm²/s.
Q3: Are three screw pumps suitable for marine applications?
Yes — they are among the most widely used pumps in the marine industry for main engine and auxiliary engine lubrication systems, fuel oil transfer, and boiler feed systems. Low noise (<70 dB), minimal vibration, and long service intervals are critical advantages in ship engine rooms.
Q4: What happens if a three screw pump runs dry?
Dry running damages the screw surfaces within seconds, as the oil film responsible for lubrication and clearance maintenance disappears. Always ensure the suction line is primed and fluid is present before startup. Most marine installations include low-pressure alarms to prevent dry-run damage.
Q5: How do I select the right three screw pump model?
Key selection parameters: required flow rate (m³/h), system pressure (MPa), fluid viscosity at operating temperature (mm²/s), fluid temperature (°C), and NPSH available. Contact our engineering team with these parameters for a model recommendation.
References
- Karassik, I. J., Messina, J. P., Cooper, P., & Heald, C. C. (Eds.). (2001). Pump Handbook (3rd ed., Chapter 3: Rotary Pumps). McGraw-Hill.
- Hydraulic Institute. (2019). ANSI/HI 3.1-3.5: Rotary Pump Standards. Parsippany, NJ: Hydraulic Institute. Available at: www.pumps.org
- American Petroleum Institute. (2016). API Standard 676: Positive Displacement Pumps — Rotary (3rd ed.). API Publishing Services, Washington, DC.
- Jiang, Y., Furmanczyk, M., Lowry, S., Zhang, D., & Perng, C.-Y. (2008). A Three-Dimensional Design Tool for Crescent Oil Pumps. SAE Technical Paper 2008-01-0003. SAE International. https://doi.org/10.4271/2008-01-0003
- ISO 2858:1975. End-suction centrifugal pumps (rating 16 bar) — Designation, nominal duty point and dimensions. International Organization for Standardization. [Referenced for dimensional and rating context in comparison with rotary pump standards.]
- China Classification Society (CCS). (2022). Rules for Classification of Sea-going Steel Ships, Part 3: Machinery Installations. Beijing: CCS. [Relevant to marine pump certification requirements.]