As the core document for characterizing the performance of chemical pumps, the performance curve diagram intuitively reflects the correlation characteristics of the pump's operating parameters under different working conditions, and serves as the fundamental basis for pump type selection, operating condition optimization, and fault diagnosis. This paper systematically analyzes the core connotation and application logic of the performance curve diagram of chemical pumps.

First, we clarify the definition of the performance curve diagram of chemical pumps: it is a set of curves plotted using data obtained from experimental tests under constant rotational speed conditions, which systematically characterizes the dynamic correlations among key technical parameters of chemical pumps, such as flow rate, head, efficiency, shaft power, and cavitation resistance. Compared with ordinary clean water pumps, the special properties of the media conveyed by chemical pumps (e.g., strong corrosiveness, high viscosity, flammability and explosiveness) determine that the accuracy of their performance curves is directly related to the safety and operational economy of the production system. Therefore, these curves are also regarded as the core technical guidelines for the operation and regulation of chemical pumps.

A complete set of performance curve diagrams of chemical pumps mainly consists of four core functional curves, each corresponding to the correlation law of specific performance parameters, with detailed analysis as follows:

1.Flow-Head Curve (Q-H Curve)

It is the core curve for characterizing the performance of chemical pumps. Herein, flow rate (Q) refers to the volume of medium delivered by the pump per unit time, commonly measured in cubic meters per hour (m³/h); head (H) refers to the effective work done by the pump on a unit weight of the medium, or colloquially, the pump’s capacity to lift a unit weight of the medium, measured in meters (m). The typical characteristic of this curve is that the head shows a decreasing trend as the flow rate increases; when the flow rate is zero, the head reaches its maximum value, defined as the shut-off head, which corresponds to the pump’s operating condition with the discharge valve closed. The shape of the Q-H curve varies with different types of chemical pumps:

①Flat curves are suitable for working conditions where the flow rate fluctuates significantly but the pressure requirement of the pipeline system is stable.

②Steeply falling curves are applicable to medium delivery scenarios prone to clogging.

③Hump-shaped curves require avoiding operation under working conditions on the left side of the hump to prevent medium backflow.

2.Flow-Power Curve (Q-N Curve)

It characterizes the quantitative law of the pump’s shaft power varying with the flow rate. Shaft power refers to the mechanical power transmitted from the motor to the pump shaft, serving as the core parameter for determining motor selection specifications and evaluating operational energy consumption. The core rule of this curve is that the shaft power increases monotonically with the rise of flow rate, and drops to the minimum value when the flow rate is zero. Based on this characteristic, chemical pumps should adopt the valve-closed startup mode during the startup phase: cutting off the flow minimizes the startup power, thereby reducing the peak startup current and preventing motor damage due to overload. Meanwhile, this curve is the key basis for motor power selection; the rated power specification of the motor should be determined by reserving a reasonable safety margin based on the shaft power value corresponding to the maximum operating flow rate.

3.Flow-Efficiency Curve (Q-η Curve)

It is the core curve representing the energy conversion efficiency of chemical pumps. Efficiency (η) refers to the ratio of the pump’s output effective power to the input shaft power, reflecting the efficiency of converting electrical energy into mechanical energy for medium delivery. The higher the efficiency, the lower the energy consumption per unit delivery volume, and the better the operational economy. The Q-η curve shows a typical peak-shaped distribution, and the peak of the curve corresponds to the pump’s Best Efficiency Point (BEP). Around the BEP, a high-efficiency operating zone is usually defined (generally covering the range where efficiency is above 92% of the BEP efficiency). When a chemical pump operates within this zone, not only is the energy consumption maintained at an optimal level, but also the wear rate of key components such as impellers and bearings can be effectively reduced, extending the service life of the equipment. Therefore, during the pump type selection process, it is essential to ensure that the actual operating point falls within the high-efficiency zone, avoiding the risks of energy efficiency attenuation and equipment failure caused by deviation from the optimal working conditions.

4.Flow-Net Positive Suction Head Curve (Q-NPSH Curve)

It is the key safety performance curve for ensuring the long-term stable operation of chemical pumps. Cavitation is a typical failure mode during pump operation. Its formation mechanism is as follows: when the pressure at the pump inlet is lower than the saturated vapor pressure of the medium, the medium vaporizes to form bubbles; these bubbles then flow to the high-pressure zone with the medium and collapse rapidly, causing impact erosion on flow-passing components such as impellers and pump casings. This not only leads to the attenuation of pump performance but also shortens the service life of the equipment. Net Positive Suction Head (NPSH) refers to the minimum net positive suction head required to avoid cavitation. The Q-NPSH curve quantitatively characterizes the minimum NPSH required by the pump under different flow conditions. During actual operation, the available NPSH provided by the system must be greater than the required NPSH corresponding to the curve to achieve cavitation protection.

After clarifying the composition system of the performance curve diagram, we further explore the interpretation logic of its practical application value. For chemical production systems, the core application value of the performance curve diagram is reflected in three dimensions:

1.Pump type matching and selection: Determine the pump type that meets the production flow rate and head requirements through curve analysis, ensuring that the operating point falls within the high-efficiency zone to achieve the unity of adaptability and economy.

2.Operating condition optimization: When the production load is adjusted, judge the pump’s operating status based on the curves, and avoid overload and low-efficiency operating conditions by adjusting the valve opening or pump rotational speed.

3.Fault diagnosis: When the actual operating performance of the pump deviates from the theoretical performance indicated by the curves, the fault direction can be accurately located, such as impeller wear, seal failure, or medium scaling. For example, if the actual head is lower than the theoretical head corresponding to the flow rate on the curve, it can be initially determined that the impeller is scaled or worn, and maintenance and cleaning work should be carried out.

It should be emphasized that the test reference conditions for the performance curve diagram of chemical pumps are specific rotational speed and standard medium (usually clean water). However, the media actually conveyed in chemical production mostly have special physical and chemical properties such as corrosiveness and high viscosity, which will cause deviations between the pump’s actual operating performance and the benchmark values on the curves. Therefore, in practical applications, the parameters indicated by the curves need to be corrected according to the physical and chemical parameters of the medium to ensure the accurate and reliable guiding value of the curves.

In summary, the performance curve diagram of chemical pumps is a core technical document for analyzing pump operating characteristics. Although its characterization form is complex, mastering its composition system and interpretation methods systematically can realize scientific pump type selection, precise optimization of operating conditions, and efficient equipment maintenance. This ensures that chemical pumps, as core fluid transfer equipment, operate in a long-term efficient and safe state, providing support for the stable operation of chemical production systems.