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Proper selection of a three-screw pump is crucial to ensure efficient and reliable operation. If the pump is not chosen correctly, it may result in unsatisfactory performance, excessive noise, vibration, and even severe damage to internal components, leading to system failure. Therefore, careful consideration must be given during the selection process. A thorough understanding of the operating conditions is essential, including not only basic parameters like flow rate and pressure but also the properties of the medium being pumped—such as its corrosiveness, gas content, solid content, particle size, temperature, viscosity, specific gravity, and whether it contains abrasive or corrosive materials. Additionally, suction conditions and installation requirements should be clearly defined.
Based on our experience, the following points should be taken into account when selecting a three-screw pump:
1. **Pump Speed Selection**
- The speed should be determined based on the viscosity of the medium and the pump's specifications. For high-viscosity fluids, a lower speed is recommended. Conversely, for low-viscosity media, higher speeds can be used.
- When the viscosity exceeds 20 °E, for large pumps (with a main rod diameter of 60 mm or more), a speed of 970 rpm or 720 rpm is appropriate. If the viscosity is above 80 °E, the speed should be reduced further, ideally between 200–500 rpm.
- For smaller pumps, if the viscosity is over 20 °E, 1450 rpm or 970 rpm is suitable. If the viscosity is higher than 80 °E, reduce the speed to 300–600 rpm.
- Higher speeds can lead to increased friction and wear, especially if the fluid has poor lubrication or contains impurities. In such cases, a lower speed (below 1450 rpm) is recommended to extend the pump’s lifespan.
2. **Structural Selection**
- Choose a built-in bearing structure for pumps handling lubricated oil at temperatures below 80°C.
- Use an external bearing structure when the temperature exceeds 80°C or when the medium has poor lubrication.
- For media with poor flowability, high viscosity, or requiring heating/insulation, select a pump with a double-layer heating structure.
- For high-temperature applications, use a pump made from high-temperature resistant materials. Please contact us for more details.
3. **Performance Relationships**
- At the same speed, the flow and pressure are approximately linearly related. As pressure increases, flow tends to decrease.
- Flow is directly proportional to speed when viscosity and pressure are constant. Similarly, shaft power is proportional to both pressure and speed under the same conditions.
- As viscosity increases, both flow and shaft power increase, but the relationship is complex. It is advisable to consult an expert if needed.
With proper selection and regular maintenance, a three-screw pump can deliver excellent performance and long-term reliability.