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How To Select The Right Pond Pump From Manufacturer's Pump Curves

In previous articles we discussed maximum flow and also maximum head and how they could easily confuse and result in the selection of a completely inappropriate pond or waterfall pump. It was also shown that as the height to which any volume of water had to be pumped increased then the flow of water would decrease ... because the need to split the fixed energy supplied by the pump's motor between flow (mass of water) and the head to which it has to be lifted.

This can be compared to your carrying a bucket of water up a ladder. You would need to expend energy but if you wanted to carry 2 buckets of water up the same level you would need to use twice as much energy. Since a pump motor cannot change the energy it must either change the flow or the height to which water can be lifted.

Pump curves show the relationship between how high a pump can deliver and the amount of water delivered at that height. Take a close look at the graphs below ...

Pump curves for two distinct ranges of pond pumps are shown below.

pump curves

The left side of the graphs shows the pump head in metres and the bottom graph axis show the amount of water indicated as "Q" and measured in lph or litres per hour.

Notice how flow drops quickly as head increases

How To Read The Graph To Pick The Right Pump

You simply read from the intersecting point of the pump pumps curves the ideal pump size or model for your system. Try to choose a point that is somewhere in the middle of the pump range. Let me give an example using graph on right hand side ... and always remember if you're not sure go for the next size up.

  • Head or height to which I need to pump = 2 metres

  • Q or volume of water I want to pump at this height = 1500 lph

  • You'll see that only 2 pumps out of the 4 curves can do this .... the uppermost 2 curves and the lower of these only just manages to perform at this duty and this ignores any pressure drop due to pipe length or fittings in the pipe system. I therefore believe the only pump that will effectively do the job required is that shown in the top curve namely the Techno 4000. Theoretically this latter pump will deliver 1500 lph of water at a head of 2.4 metres.

  • Study this example until you're very clear on how to use a pond pump curve to select the ideal pump for your filter or waterfall.

When buying submersible pumps to use in garden goldfish or koi ponds consider these items:

  1. Long 3-core cable on the submersible pumps to prevent unnecessary joining of cables. Do not buy water feature or aquarium pumps for use in a pond. This type of pump generally is in a small box, has a short and often only 2-core cable.

  2. Good instructions and performance details are supplied for the submersible pump box.

  3. Compliance with the country's electrical certification standards for submersible pumps.

  4. Low power consumption (look for details of the wattage or at least amps. Know how to check the running cost and compare pumps from different suppliers

  5. Minimum of 2 years guarantee displayed openly. The longer the guarantee the more you can be assured that the pump you buy is reliable.


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