You may not be familiar with the term “pond pump head.” In essence, it means what pressure is the pump capable of producing. Therefore a pump with a maximum head twice that of another can safely be assumed to be more powerful … but be careful because you need to know much more than a relative impression of power.
In fact, the only usefulness of the term maximum head is to be able to make a quick and approximate comparison between pumps of the same model range. You cannot safely use this information in comparing pumps from different manufacturers.
What is the Pump Head?
Water pump head refers to the pressure that must be generated by a pond pump in order to run a fountain, waterfall, filter, and other pond components. Most garden fish pond pumps are what we call submersible centrifugal designs. In this type of pump, an impellor or rotor spins at a very high speed. This action transfers energy from the pump motor to the water that flows into the rotor cavity and this creates pressure by centrifugal force.
This pressure forces water out of the pump casing and delivers it to whatever height is necessary to run your pond components, including a waterfall if you have one. Pumps of this kind have an impellor rotation speed that is normally constant. This means the energy available for driving water is constant. In practical terms, this amount of constant energy can be divided as follows:
- Utilize the motor energy to pump more water volume (or mass) to a lower head (height)
- Utilize the motor’s energy to pump lower water volume (mass) to a greater height (head or pressure)
It’s a bit like your own body … you can carry 25 lbs much further than you can carry 50 lbs
You’ll always see pump head information on the manufacturer’s product box.
Using and understanding these two important pump options will enable you to quickly determine the water pump specifications needed for your garden fish pond design or project. You can physically demonstrate the impact of the pump head on water volume delivery by doing the following:
How Pump Head Changes Water Flow Rate
To see the effect of the pump head in action do the following…
- Attach a length of garden hose to your fish pond pump (say 10 feet or so)
- Place the pump in your pond or other water reservoir and hold the end of the hose at the water surface level. Note quite a lot of water flows out of the hose.
- Now, lift the end of the hose slowly above the surface of the water. You will see that as the hose rises higher into the air, the flow of the water decreases
- Continue to slowly increase the height of the hose outlet.
- You will notice an ever-decreasing flow out of the hose until you reach a point where the flow stops altogether.
- If the pump you’re testing is fairly small, with a low maximum head, you might reach this no-flow point (maximum head) at 4 feet or less.
- For a stronger pump, you might have to stand on a ladder to reach this point.
Pump head is just another term for pump pressure
Think of your water pump as the height to which the water will be pumped, either to the top of your waterfall, fountain, biofilter, or other component. You always measure this head or height distance FROM THE SURFACE OF YOUR POND (not the bottom where your pump resides) AND THE INLET TO YOUR WATERFALL.
To buy the right pump for your pond system you will have to determine the correct water pump head applicable to your unique circumstances. take into account that the higher the head, the less water volume because energy from the pump motor is constant.
This relationship between the pump head and water flow rate is very important, and you’ll need to know it in order to choose the correct pump for your pond application, especially if you plan on having a waterfall with your pond.
Most good manufacturers provide a table or graph this is reproduced here (below is an extract from the Oase Nautilus fountain catalog)
|Nautilus Pump Model||Pond Surface (Maximum Flow)||1.0m||1.5m||2.0m||3.0m||5.0m||Max Head|
Another important consideration is the other garden pond components your pump will be supplying. When water is pumped through a pipe or tube with any kind of fittings, as in “T” fittings, in-line UV lights, etc. then some of the energy and pressure from the water pump is lost due to the restrictive nature of forcing the water through these fittings.
You need to take this pressure loss into account when determining the total water pump head of your pond system. This head loss is also known as friction loss. In practical terms, if you have a small pond system with short lengths of pipe and relatively few bends and fittings this friction loss can almost be ignored as long as you do the following:
- Use lengths of pipe or hose less than 10 feet (3 meters) long
- Use pipe or hose with a diameter of less than 1 inch (25mm)
Use ribbed pipe. This type of pipe doesn’t restrict pump flow when bent, as is often required in a garden pond application.
There are additional factors you’ll need to take into account when choosing a pump, not the least of which is the pump flow needed for your pond. This pump flow will depend on whether or not you have a waterfall, if you plan on keeping koi or other fish in your pond, if you’ll be running a fountain, etc.
It’s always a good idea to choose a pond pump one size larger than you think you might need. This allows for uncertainties and extra pipe lengths for example.
Most fish ponds have a waterfall and need a biofilter. It is normally the case that the basis upon which a pump is specified in this kind of situation is based on the needs of the waterfall and not the biofilter. Generally, the flow down a waterfall is more than that required by a biofilter. By understanding this it is possible to save money. A biofilter needs water 24 hours per day but a waterfall can be closed down whenever it suits the pond keeper. Hence a small pump can be used 24 hours per day and the larger waterfall pump as many hours as you choose.