When to Use a Submersible Pond Pump
When deciding on a pump for a pond project, you can either choose a submersible pond pump or an external pump. As you may have guessed, a submersible pump is installed and operated beneath the surface of the pond, and an external pump sits outside of the pond in a dry location.
Both systems have certain strengths and weaknesses that'll you'll have to look at before deciding which system is right for your particular project. Whichever system you end up going with, make sure to purchase a good quality, reliable pump that can be trusted to run 24-7, 365 days per year. Since the pump will drive the main filtration system in your pond, a healthy pond ecosystem depends on a pump's continued, reliable operation.
How Pond Pumps Work
Submersible pond pumps run on a fairly basic principle when broken down. An electric motor is used to drive an impeller. As the impeller turns, water is drawn in one side of the pump, and is expelled out the other. The amount of water flow is determined by the power and size of the impeller. The larger the impeller, the more water can be pumped. Of course, as the impeller gets larger, a more powerful electric motor will be required as well; which in turn uses more electricity.
Why Use a Submersible Pond Pump
There are a few advantages that submersible pond pumps have over external varieties. The first is, because submersible pumps are kept submerged in water, no priming is necessary. With external pumps, care must be taken to ensure there is water in the pipes before turning on the pump to prevent the pump from sucking in air and burning out. Another advantage of submersible pumps is they are quite easy to hide in a pond due the pump being stored under the water. In the case of an external pump, it takes a little extra effort to hide the pump somewhere in the landscaping, while keeping the pump accessible for maintenance.
Limitations of Submersible Pond Pumps
Sometimes if a pump needs to be placed in an area of limited size or clearance, it may be difficult to fit an entire submersible pump. In these situations it is much easier to place an intake pipe (which is much smaller than the pump itself), which leads to an external pump. An example of such a situation would be a skimmer. In order to get water flowing through the skimmer to capture floating debris, some kind of pump is needed inside the skimmer to draw water in. If the skimmer is large enough, you can place a submersible pump directly inside the skimmer. If either the pump is too large, or the skimmer is too small, then an external pump may be needed. To learn more, please see our page on external pond pumps.
How Large a Pump is Needed?
Whether you decide to go with a submersible pond pump or not, you will still need to figure out how much water is in your pond so you can purchase an appropriately sized pump. As a minimum your pump should be capable of pumping the entire contents of your pond in two hours. If you plan on putting koi or another type of fish in your pond, then turning over the contents of your pond more often, such as every hour, is a good idea. Also, keep in mind that pump flow rates are measured assuming there is no extra strain on the pump due to gravity or pipe fittings. In the case that you are pumping water up hill (ie. for a waterfall), you will need to take this additional 'head pressure' into consideration. For more information on calculating the head pressure in your pond, please see our page on Calculating Pond Head Pressure.