External Pond Pumps
Selecting the Correct External Pond Pump
Most professionals and consumers alike select a submersible pump for their pond and waterfall installations. This article will address a different type of pond pump used by installers that may have considerable advantages over submersible pumps in many specific applications. The external pond pump is an invaluable tool for our trade and one that is often overlooked as an installation option.
What is an external pond pump? While the types and features of external pond pumps may vary the definition remains constant. An external pond pump is one that sits outside of (or external to) the pond itself. Applications for these pumps include, but are not limited to, waterfalls, pulling from bottom drains, formal fountains, pond circulation, or any situation where a submersible pump is not practical or attractive.
One type of external pond pump is a magnetic coupled asynchronous pump. These pumps may be used both as submersible and as external in-line pumps and feature tubing ready intakes and outlets. These are often used on smaller ponds, tanks and wall fountains. New technologies are improving this type of pump and although they are not the focus of this article they may one day become a more widely recognized choice for certain external applications.
The other type of pump is the more widely recognized centrifugal pump. Traditional motor driven external pumps will range in volume from under 2000 gph to giant 3 HP pumps capable of delivering tens of thousands of GPH flows. These pumps are divided into multiple categories, which have created confusion for some prospective buyers on how to proceed.
External pumps are divided into flooded suction or self-priming. They are also divided into high flow- low head or high flow – high head. Additionally they may be either 115 volt or 230 volt or, as many do, can be operated at either voltage. External pumps can be single speed or multiple speeds. With so many choices available it is little wonder that consumers and installers alike must take great care in choosing the correct pump for each specific application.
Low Head and High Head External Pumps
The selection of either a high head or low head external pump depends upon the height of the water feature it is intended for. If building a 3-4´ high waterfall or running to a pressurized filter it is very likely that a low head external pump will be perfect for the job. If supplying a 20´ tall waterfall or moving through a very long run of pipe you may be looking at the need for a high head external pump. The first step in determining the correct type of pump will be to calculate your total dynamic head. That includes calculating for the height of the water feature, the length of the run, the inside diameter of the pipe used, and the number and type of fittings such as elbows or Y’s that will be used in the plumbing. Several industry charts provide directions for calculating the total dynamic head and this article will not delve into those calculations. (See Dynamic Head Box)
Once you have your total dynamic head pressure (TDH) for your installation you can then determine the GPH flow required at the TDH and consult the flow charts of any of the external pumps on the market. According to Rick Smith of Easy Pro Pond Products, “Each external pump will have a chart with the GPH flow at various head heights. By matching up your requirements to these charts you can select the best external pump for your job.” Rick g