What is a Pump Curve?
A pump curve shows the relationship between capacity (liters per hour) and head height (meters). The horizontal axis shows how much water the pump moves, the vertical axis shows how much pressure (in meters) the pump delivers. The higher you have to pump water or the more resistance there is, the lower the final capacity becomes.
The curve runs from the top left (maximum pressure, no capacity) to the bottom right (maximum capacity at 0 meters height). Your actual capacity can be found by determining the total resistance in your system and reading this point on the curve.
Get Started Quickly: Reading a Pump Curve
Requirements:
- Pump curve of your pump (found in the product description)
- Calculated resistance of your system (height + hose resistance + filter resistance)
Steps:
- Determine the total head height. Add the height difference (in meters) to the resistance of hoses, couplings, and filters. For calculating hose resistance, see calculating resistance for pond pumps.
- Find this number on the vertical axis. This is the y-axis of the graph, usually displayed on the left in meters (m).
- Draw a horizontal line to the pump curve. The intersection with the curve represents your operating point.
- Read the capacity on the horizontal axis. Draw a vertical line down from the intersection. This number (in L/h or m³/h) is the actual capacity of your pump in your situation.
- Compare with your required capacity. Check if the read capacity meets what your pond needs (minimum 1× pond volume per hour for filter circulation).
Tip: Always round resistance values slightly upwards, so you keep a safety margin and are not at the lower limit of capacity.
Common Mistakes
- Only look at maximum capacity: this number only applies to free flow (0 meters). In practice, you always have resistance and the actual capacity is lower.
- Forgetting height difference: a pond hose has resistance of itself, but the most important resistance comes from the height difference between the water level and the outlet of your hose. Always include this.
- Underestimating filter resistance: a pressure filter or UV-C unit adds significant resistance. Always check the specifications.
- Dimensioning too tightly: Choose a pump that is well above your minimum needs. Capacity decreases as filters become dirty and pumps wear out.
Example: Reading a Pump Curve
Suppose your filter is 1.5 meters higher than your pond, you use 5 meters of hose (example resistance 0.3 m) and a pressure filter (resistance 0.5 m). Total head height = 1.5 + 0.3 + 0.5 = 2.3 meters. Find 2.3 m on the vertical axis, draw a line to the curve and read the capacity. If that is for example 4,000 L/h, then you know that your pump in this situation moves 4,000 liters per hour (not the specified maximum capacity of the pump).
Note: Some graphs show multiple curves (for different pump settings or models). Always check which curve belongs to your pump.
Troubleshooting
- Read capacity too low? Reduce the resistance by using shorter or wider hoses, reducing bends, or choosing a more powerful pump.
- Operating point falls outside the curve? The resistance is too high for this pump. Choose a pump with a higher head height or reduce the resistance in your system.