Chemical pump selection
**Abstract:**
When selecting a pump, it is essential to consider the specific characteristics of different types of pumps. Pumps can be broadly classified into two main categories based on how they act on the liquid: **rotodynamic (vane) pumps** and **positive displacement pumps**. Rotodynamic pumps, such as centrifugal, axial, and vortex pumps, operate by using the centrifugal force generated by rotating blades to draw in or expel the liquid. On the other hand, positive displacement pumps, like piston, plunger, and rotary pumps, use the reciprocating or rotational motion of components such as pistons or rotors to compress and move the liquid.
Centrifugal pumps are suitable for liquids with a viscosity below 650 mm²/s, as higher viscosities can significantly reduce efficiency. However, in some cases, such as in chemical production, centrifugal pumps are still used for liquids with viscosities up to 1000 mm²/s due to their smooth flow, simple control, and lack of pulsation. When dealing with liquids containing gas (up to 5% volume), the performance of centrifugal pumps may decrease, leading to noise, vibration, and even mechanical failure if not properly managed.
For high-viscosity fluids (above 650 mm²/s), positive displacement pumps are more appropriate. These include reciprocating pumps, metering pumps, and screw pumps. Metering pumps are ideal for precise dosing, while diaphragm pumps are preferred for leak-free operation. In low-temperature, stable-pressure applications, rotor or twin-screw pumps are often selected.
Pump selection also depends on the required flow rate and head. Centrifugal pumps are generally preferred due to their simple design, ease of flow adjustment, and absence of pulsation. After determining the type, the specific model and materials should be chosen based on process parameters and the nature of the fluid. Manufacturers' technical data and samples are then used to finalize the pump specification.
When handling gas-containing liquids, measures must be taken to minimize gas content to ensure reliable pump operation. This includes proper suction tank design, pipe layout, and avoiding air pockets. For solids-laden liquids, special centrifugal pumps such as slurry pumps are needed. For volatile liquids, factors like inlet pressure, vapor pressure variation with temperature, and seal integrity must be carefully considered.
For non-leakable applications, hermetically sealed pumps such as magnetic drive or shielded pumps are recommended. Magnetic drive pumps offer better protection against leakage but require more maintenance compared to shielded pumps.
Keywords: Pump selection, chemical engineering, centrifugal pump, positive displacement pump, pump performance, fluid dynamics
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