Chemical pump selection

**Abstract:** In the selection of pumps, it is essential to consider the characteristics of different types of pumps. Pumps can be broadly classified into two main categories based on the principle by which they act on the liquid: **rotodynamic (vane) pumps** and **positive displacement pumps**. Rotodynamic pumps operate using the centrifugal force generated by rotating blades to draw in or discharge the liquid. On the other hand, positive displacement pumps use the reciprocating or rotational movement of a piston or rotor to compress and move the liquid. Rotodynamic pumps are further categorized into centrifugal pumps, axial pumps, and vortex pumps. Positive displacement pumps include piston (plunger) pumps, rotary pumps, and others such as gear pumps and screw pumps. When selecting a centrifugal pump, it is important to consider the liquid’s temperature and viscosity. The operating temperature should not exceed 650 mm²/s; otherwise, pump efficiency may significantly decrease. For viscosities above 650 mm²/s, centrifugal pumps are generally not recommended due to performance degradation. However, in chemical production, centrifugal pumps are still commonly used for liquids with viscosities up to 1000 mm²/s because they provide smooth flow, no pulsation, and simple flow control. For applications requiring large flow rates but relatively low head, a flat flow-head curve centrifugal pump is suitable. If flow changes are minimal and head variations are small, a steep flow-head curve centrifugal pump is preferred. Positive displacement pumps are ideal for high-viscosity fluids, typically above 650 mm²/s, where smaller flow rates and higher heads are needed. Reciprocating pumps are often chosen for such conditions. When accurate measurement is required, plunger metering pumps are suitable. For leak-free operation, diaphragm metering pumps are preferred. Liquids with poor lubrication properties should avoid gear and three-screw pumps, and instead, use reciprocating pumps. For low-temperature, stable-pressure applications, rotor or twin-screw pumps are appropriate. The selection of a pump also depends on the system's required flow and head. Centrifugal pumps are favored for their simple structure, lack of pulsation, and ease of flow adjustment. Unless specific conditions make them unsuitable, they are often the first choice. Once the type is determined, the pump series and materials are selected based on process parameters and the nature of the medium. Finally, pump models are chosen based on manufacturer samples and technical data. For special media, such as gas-containing liquids, pump performance—flow, head, and efficiency—can deteriorate significantly with increasing gas content. Higher gas levels may lead to noise, vibration, corrosion, and even mechanical failure. To ensure reliable operation, measures should be taken to reduce gas content in the liquid. Pump suction systems must be designed carefully. Suction tanks and pipes should be arranged to allow equal liquid intake, and the pump inlet should be submerged to a certain depth to prevent air ingestion. Inlet and return pipes should be positioned away from the pump suction port to avoid drawing in undissolved bubbles. Pipes should not be placed near the center or too close to the tank wall, ideally at least 1.5 times the pipe diameter from the wall to prevent vortices. All connections must be sealed properly to prevent air leaks. When handling liquids with solid particles, the presence of solids reduces pump efficiency and head, as these particles do not transfer energy like the liquid itself. For easily vaporizable liquids, factors such as high inlet pressure, temperature-dependent vapor pressure, and strict sealing requirements must be considered. For non-leakable liquids, hermetically sealed pumps—such as magnetic drive or shielded pumps—are recommended, or mechanical seal pumps equipped with leak detection and alarm systems. Magnetic drive pumps have a thicker isolation sleeve compared to shielded pumps, offering an extra layer of protection against leakage. Keywords: Pump selection, chemical industry, centrifugal pump, positive displacement pump, viscosity, flow, head, gas content, leak-proof design. **Previous:** Solar heat pump technology and its heating applications **Next:** Innovation ability to enhance Zhejiang to "manufacturing province" **Related links:** - Solar heat pump technology and its heating applications - New Germany industrial pump company identifies new high-temperature screw pump - Domestic valve industry urgently needs high-precision science and technology support - Concrete pump fault causes and troubleshooting of tube plugging - Jet pump application in process lubrication system and vacuum test

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