The performance curve of a centrifugal pump gives you an idea of how this machine operates and what actual performance it achieves in its daily tasks. That’s why it’s important to know how to interpret how it operates and what each of the readings we periodically take indicates.

We always recommend paying attention to the performance curve of a centrifugal pump . It is a graph that represents the unique relationship between head and flow rate that the pump guarantees at a certain impeller rotational speed, and its reading varies depending on the task the pump is performing.

centrifugal pump performance curve

Why should you take into account the performance curve of your centrifugal pump?

centrifugal pump performance curve

Currently, the market allows customers to acquire a pump model that enables us as manufacturers to select the characteristic curve of a centrifugal pump based on the operating point at which this element will be placed.

It is essential to be clear that there are two types of pump curves, those of centrifugal pumps and the curves of positive displacement pumps.

Thus, centrifugal pumps account for 70% of pumping applications. To read it correctly, the user should be aware that their curves typically have a crescent shape. In other words, the highest point on the left indicates the maximum working pressure but the lowest flow rate, while the right end of the graph represents the highest flow rate the pump can provide but the minimum pressure.

Another aspect to consider is the operating point, which is typically established with the indicated efficiency in percentage.

The importance of reading the performance curve of a centrifugal pump

The performance curve of the centrifugal pump displays various operating points that this component can achieve. You should bear in mind that not understanding this can lead to many installation problems.

It is essential to know that if a pump’s operating point is too far to the left on its curve, its capacity cannot be increased if a pressure calculation error is detected.

On the other hand, if it is too far to the right, there is a risk of cavitation, which in practice could damage the pump casing and lead to liquid boiling.

For added peace of mind, one should make a selection that allows for a 10% safety margin to the left of the operating point, ensuring that the pump can operate under various conditions, as performance can be reduced but never increased.

There are a number of basic parameters that must be taken into account for a correct reading of the performance curve of a centrifugal or positive Displacement Pump:

  • Operating Points: The curve displays the various operating points that the pump can reach. Ignoring or misinterpreting this information can result in serious problems during the installation phase and during the subsequent operation of the equipment. For instance, an operating point too far to the left indicates performance below optimum, making it challenging to increase capacity in case of a pressure calculation error.

  • Cavitation Risk: Conversely, if the operating point is located too far to the right, the pump runs the risk of experiencing a phenomenon known as cavitation. This is a process where vapor bubbles form in the liquid, and when they collapse, they can generate shockwaves capable of seriously damaging the equipment, affecting the pump casing, and causing the liquid to boil.

  • Safety Margin: From an engineering perspective, it is prudent to operate with safety margins. In the case of centrifugal pumps, a 10% margin to the left of the performance curve is recommended. This margin ensures that the pump can adapt to potential changes in operating conditions.

Other references from the performance curve:

  • Standard Reference: Often, the curves are based on tests conducted with fresh water at 20°C and at sea level. However, in industrial applications, it’s rare to work exclusively with water. It is imperative to adjust or reinterpret the curves based on the actual fluid that will be pumped.

  • Viscosity and Specific Gravity: Viscosity and specific gravity are fundamental properties that can significantly affect the performance of a pump. Fluids with viscosities different from water (the usual standard) will require a more thorough analysis. Furthermore, it’s important to note that some fluids have viscosity specifications at different temperatures, which can influence the operation and durability of the pump.

  • Operating Temperature: The temperature at which the pump operates may vary from standard conditions (20°C or 60°C). Temperature differences can affect the viscosity of the fluid and, consequently, the performance of the pump. It’s crucial to adjust performance expectations and calculations based on the actual operating temperature.

centrifugal pump performance curve

For industrial engineers, the performance curve is not just a graph; it is a fundamental tool to ensure the efficiency, safety, and durability of centrifugal pumps. Its proper interpretation is vital to avoid unplanned shutdowns, equipment damage, and additional costs. It is an investment in knowledge that provides tangible returns in the field of engineering

The value of the motor revolutions of your centrifugal pump

The revolutions of the motors in centrifugal pumps vary depending on the motor’s poles. The more poles, the slower it will run.

Increasing them allows the pumps to generate more flow at lower pressures, thereby reducing the required NPSH.

This also serves to use a smaller motor and experience less wear. On the other hand, if the goal is higher pressure, pumps with lower flow rates will operate at higher RPMs in order to achieve the required pressures.

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