How to Read a Pump Curve

A pump curve shows how a pump will perform at different flow rates. It is one of the most important tools when selecting, checking or troubleshooting a pump.

The main thing to understand is this:

As flow increases, head usually decreases.

In simple terms, the pump can either move less liquid at a higher pressure, or more liquid at a lower pressure.

1. Flow Rate

Flow rate is usually shown along the bottom of the curve.

This may be shown in:

• L/min
• m³/h
• L/s
• GPM

Flow tells you how much liquid the pump is moving.

2. Head

Head is usually shown on the left-hand side of the curve.

Head is the pressure the pump can generate, expressed as a height of liquid. In Australia, this is usually shown in metres.

For example, if a pump is producing 30 metres of head, it does not mean the pipe must be 30 metres high. It means the pump is generating enough pressure to overcome the total resistance in the system.

3. Duty Point

The duty point is where the required flow and required head meet on the pump curve.

This is the point where the pump is expected to operate.

For example:

Flow	Head
20 m³/h	35 m

If the pump curve passes through this point, the pump may be suitable.

If the curve is well above or below the duty point, the pump may be oversized or undersized.

4. Best Efficiency Point

Most pump curves will show a Best Efficiency Point, often called the BEP.

This is where the pump operates most efficiently and usually with the lowest stress.

Running too far away from the BEP can lead to problems such as:

• Higher vibration
• More noise
• Increased wear
• Seal or bearing issues
• Poor energy efficiency

A pump does not always need to run exactly on the BEP, but it should operate reasonably close to it where possible.

5. Power Curve

Some pump curves also show the power required.

This helps confirm that the selected motor is large enough for the pump.

The motor should have enough power for the full operating range, not just one point on the curve.

6. NPSH Curve

The NPSH curve shows how much suction pressure the pump needs to avoid cavitation.

Cavitation can cause:

• Noise
• Vibration
• Loss of performance
• Impeller damage
• Premature pump failure

The system must provide more NPSH than the pump requires.

Final Tip

A pump curve should not be read in isolation. It needs to be compared against the actual system, including pipework, fittings, valves, elevation, liquid properties and required flow.

A pump may look suitable on paper, but if the system conditions are wrong, it may still perform poorly.

The pump curve tells you what the pump can do. The system curve tells you what the system needs. The correct selection is where the two work together.