Let’s see Together how to Read Pump Curves
The performance of a centrifugal pump is shown by a set of curves.
The performance curves of a centrifugal pump show the following functions:
▸ the Head or the manometric pressure often express in metres of water or bars.
▸ the Power consumption
▸ the Efficiency
▸ the NPSH
All of those elements being a function of the flow.
Head and QH Curve
The QH curve, also known as the pump performance curve, illustrates the relationship between the head generated by the pump and the flow rate. Head, typically measured in meters of liquid column.
In the case of a centrifugal pump, as depicted in the chart, an increase in flow rate leads to a decrease in head. Conversely, a reduction in flow rate results in an increase in head.
This inverse relationship is a key characteristic of centrifugal pumps, which needs to be considered when selecting a pump for specific applications to ensure appropriate performance and efficiency.
Power
It is important to distinguish the 3 level at which the power consumption is measured.
▸ The electrical power of the motor or P1
▸ The mechanical power delivered by the motor to the the pump shaft or P2
▸ The hydraulic power delivered by the pump or PH
Usually pump data sheets cover only the pump part.
This means that the power consumption indicated is the power P2 or the mechanical power delivered at the shaft of the pump.
Efficiency, the η-Curve
Efficiency in pumps, (ηP), is the ratio between the power delivered by the pump to the water and the power input to the pump shaft (P2).
The efficiency curve illustrates that the efficiency varies depending on the pump’s duty point.
Select a pump that matches the flow and pressure requirements and ensures operation within the most efficient flow area.
NPSH-Curve
The NPSH (Net Positive Suction Head) value of a pump represents the minimum absolute pressure required at the suction side to avoid cavitation.
This value is measured in meters and is flow-dependent; as the flow rate increases, the NPSH value correspondingly increases.
Review the Curves
The data sheet provides a complete set of pump curves.
First, determine the flow (Q) and head (H) required by your system to ensure the duty point is within the high-efficiency area of the pump curve.
Next, examine the power consumption to identify the required P2 power and select an appropriate motor that can deliver this power.
Finally, verify that the NPSH available (provided by the system) is sufficient to meet or exceed the NPSH required by the pump, thus preventing the risk of cavitation.
SPS Pumps is at your Disposal
Selecting a pump is a multi-criteria exercise that is not all that simple as one can see from our wiki.
As you discovered from the Life Cycle Costs of a pump, a poor choice can lead to huge costs when viewed on the time span during which the pump is going to operate.
SPS Pumps is the ideal partner for industry. We offer unrivalled technical support and in-depth knowledge of centrifugal pumps, as well as other types of pump.
Our expertise guarantees you reliable and efficient solutions tailored to your needs.
We also have a very wide range of spare parts in stock.
With SPS Pumps, you have a trusted partner committed to optimising your fluid handling systems.
Call us at +32 2 657 23 53 or send us an e-mail at info@sps-pumps.com.
The content of this webpage is inspired by and sourced from the Grundfos Pump Handbook, including the accompanying charts.
