# Selection of Twin‑Screw Pumps The selection of twin‑screw pumps should be based on core factors including the properties of the pumped medium, operating parameters, installation environment, as well as equipment reliability and cost‑effectiveness. The key considerations are as follows: ## 1. Clarify the Core Properties of the Pumped Medium ### Viscosity Twin‑screw pumps are suitable for a wide viscosity range (typically 1–1,000,000 cSt), but different viscosities require different pump structures. - Low‑viscosity media (e.g., light oil): pumps with high‑precision clearance design to reduce internal leakage. - High‑viscosity media (e.g., asphalt, polymers): large‑lead screws with variable‑frequency motors to avoid overload. ### Corrosiveness and Abrasiveness - Corrosive media (e.g., acid/alkali solutions, chemical raw materials): screws and casings in corrosion‑resistant materials such as stainless steel (316L) or Hastelloy. - Media containing solid particles (e.g., sandy crude oil, slurry): screws with wear‑resistant coatings (e.g., nitriding treatment). The allowable particle size must be observed to prevent jamming. ### Gas Content and Solid Content - High gas content (e.g., oil‑gas mixture): twin‑screw pumps with gas‑liquid mixing capability, plus gas‑liquid separators or return lines at the inlet. - High solid content: eccentric twin‑screw pumps (stronger particle resistance than standard types) are preferred. ### Temperature - High‑temperature media (e.g., high‑temp heat‑transfer oil, molten resin): high‑temperature alloys with cooling systems for shaft seals and bearings. - Low‑temperature media (e.g., LNG): low‑temperature‑resistant steels (e.g., low‑temp stainless steel) to avoid brittle fracture. ## 2. Match Operating Parameters ### Flow Rate and Head Select the pump model according to the rated flow (m³/h) and head (MPa). - Flow is proportional to speed; head is positively related to viscosity. - A safety margin of **10%–20%** is recommended to accommodate fluctuations. ### Inlet and Outlet Pressure - Inlet pressure: ensure sufficient pressure to prevent cavitation; use boosting devices or lower the installation height if pressure is too low. - Outlet pressure: match the pipeline pressure rating; install safety valves and relief circuits for overpressure protection. ### Speed Control - Low speed: longer screw life, lower noise. - High speed: higher flow, but must not exceed the rated speed to avoid accelerated wear. - Variable‑frequency drives are recommended for media with large viscosity variations. ## 3. Focus on Pump Structure and Seal Selection ### Screw Type - Same‑rotation twin‑screw pumps: for clean, low‑viscosity media; high efficiency. - Counter‑rotation twin‑screw pumps: for particle‑containing, high‑viscosity media; strong impact resistance. ### Sealing Method - **Mechanical seals** (single / double): for general conditions. Double seals are used for toxic, flammable, explosive, or corrosive media, requiring a sealing fluid system. - **Packing seals**: for negative pressure or easily leaking conditions, but require regular replacement. ### Installation Structure - Horizontal: high stability. - Vertical: space‑saving, suitable for tank bottom discharge. - Confirm inlet/outlet connections (flanged / threaded) match the pipeline. ## 4. Consider Installation, Operation and Maintenance ### Installation Requirements - Inlet pipelines should be short and straight to minimize resistance and cavitation. - Allow sufficient space for maintenance and disassembly. - Heat tracing (steam or electric) for easily solidified media to prevent clogging. ### Power Matching - Motor power matched to shaft power to avoid over‑ or under‑capacity. - Explosion‑proof motors with protection grade **not lower than IP55** for hazardous areas (oil, gas, chemical applications). ### Maintenance Cost - Choose brands with common wearing parts (screws, seals) to reduce spare parts costs. - Prefer modular structures for easy on‑site disassembly and repair. ## 5. Compliance and Brand Reliability - For chemical, food, pharmaceutical and other industries, select pumps meeting applicable standards: - Food‑grade: FDA certification - Chemical pumps: GB/T 3215 - Select reputable brands with complete after‑sales service for timely technical support and spare parts supply.
