Archive for July, 2010
Submersible Pump
Saturday, July 31st, 2010
How to Choose a Pond Pump
The pond pump is truly the “heart” of your pond. They are needed for a variety of functions – from general circulation to powering water features. The good news is there are a wide variety of pond pumps available from very reputable manufacturers. For just about any use, there will be multiple products available to choose from. The bad news is selecting the right pump for your needs can be a very daunting task. In this article we will provide you with a solid foundation to select the right pump for your pond application.
Uses of Pond Pumps
Pond pumps are used in four main applications:
Pond Circulation: All ponds require water circulation in order to maintain a healthy aquatic environment and to prevent stagnation. Even if your pond does not include a Water Fall, Pond Filter, or pond fountain, a pump is needed to circulate the water. Moving water provides oxygenation, prevents thermal layer turnover, reduces algae growth, and prevents mosquitoes from laying eggs on the water surface.
Pond Filters: A very common pond pump application is for use with pond filters. In this application the pump provides the water flow through the filter, ensuring the optimal amount of toxin removal.
Pond Water Features: If your pond includes a waterfall, pond fountain, or statuary fountain, a pump is required to provide the water flow for the feature. One of the great aspects of water features is that they provide multiple benefits to your pond’s aquatic environment. Water features provide not only circulation and aeration, but some also provide filtration – such as a waterfall weir with an integrated filter.
Pond Aerators: Pond air pumps are a great solution for applications that require oxygenation, but when water flow is undesirable. The most common pond Air Pump application is pond winterization. Used in conjunction with a pond deicer, the air pump provides a constant flow of oxygen and gas exchange to the pond without a flow of water which only makes the pond colder.
Types of Pond Pumps
Submersible Pumps: Submersible Pond Pumps are installed completely underwater, typically in the deepest part of the pond. This class of pump is generally suited for smaller ponds, or for water features requiring less that 4,000 GPH. The main benefit of a submersible pumps is that they are visually unobtrusive and run very quietly. They are also very easy to install, just make sure the cord length is sufficient for your needs. The downsides to a submersible pond pump is that they must be frequently removed from the pond for cleaning and maintenance. They also generally cost more to operate than an external pond pump, although there have been some significant improvements recently in submersible pump energy efficiency.
External Pumps: As their name implies, External Pond Pumps are designed to be installed outside of the pond, or “in-line”. External pond pumps are a better choice for medium to larger ponds. They can handle greater water flows (4,000 to 10,000 GPH) and are less costly to operate. Other benefits of an external pump include ease of maintenance, longer average life, and the ability to replace parts as external pumps are not encased in resin like a submersible pump. On the downside, an external pump takes more time and effort to install, they must be camouflaged from view, and they are generally more expensive than submersible pond pumps.
Direct Drive Pumps: Direct Drive Pond Pumps are more common to external pumps as they have the ability to draw water toward them. Direct drive pumps are appropriate for applications which require a significant amount of head height – such as pumping water upslope for a waterfall. They are generally more costly to operate than a magnetic drive pond pump, but in many cases they are the only choice when a substantial amount of water flow is needed. If you are purchasing a submersible direct drive pump, be sure that it is oil free, as leaking oil can harm Pond Fish and aquatic plants.
Magnetic Drive Pumps: Magnetic Dive Pond Pumps (or Mag Drive Pumps) are usually designed as submersible pumps as most are unable to draw water into the pump. The power is created through an electromagnetic field which turns the impeller. Their main benefit is energy efficiency and a longer useful life. In addition, Mag Drive pond pumps are easy to repair as typically all that is needed is a magnetic shaft and impeller (the only moving parts). The downsides are they cannot provide sufficient water flow for high head applications, and they are slightly more expensive than direct drive pond pumps. In general, if you do not have a high head requirement and are looking for a submersible pump, the magnetic drive pond pump is the best choice.
Air Pumps: Air Pond Pumps do not provide any water flow. They draw air into the pump then diffuse it into small bubbles. Air pumps are most commonly used for pond winterization as they provide oxygenation and gas exchange without providing water flow.
Choosing the Right Size Pond Pump
To choose the right size pond pump, first determine the proper application category: 1) Filtration and Recirculation; or 2) Water Features.
Filtration and Recirculation: The general rule of thumb for filtration and recirculation applications is the pump should turn the pond water over a minimum of once every two hours, and ideally once an hour. For example, if your pond is 3,000 gallons the ideal pump size is 3,000 GPH, but not less than 1,500 GPH. My personal preference is to always err on the high end of the range. A pump’s flow can always be slightly restricted, but never increased. Also, make sure your pump is the right size for your pond filter’s specifications.
Water Features: Choosing the correct pump size for a water feature is a bit more involved. The first step is to determine how much water flow you need at the discharge point of the water feature itself. Let’s use a waterfall as an example as this is the most common water feature. For each inch of waterfall width you need 100 to 150 GPH. So, if you have a 14” wide waterfall weir you will need 1,400 GPH to 2,100 GPH of water flow over the lip of the weir.
The next step is to calculate the head height. Head height refers to the approximation of the vertical and horizontal distance the water must travel from the pump to the top of the waterfall. Horizontal distance is calculated at a 10:1 ratio, while vertical distance is calculated at a 1:1 ratio. For example, if the horizontal distance from the pond pump to the waterfall is 30’, this equates to 3’ of head height. If the vertical distance from the pump to the top of the waterfall is 7’, this equates to 7’ of head height. Therefore, the total head height for this application is 10’.
The last step is to review the manufacturer’s power curve for the type of pump you have selected to determine the appropriate pump size. Let’s use the Cal Pump Mag Drive as an example. The PWM3900 model is rated at 4,100 GPH of water flow at the pump discharge, but is rated at 2,280 GPH of water flow at a 10’ head height. This would be a good choice for this particular example. Remember, it is always better to err on the high end of the GPH range as this will put less strain on the pump.
About the Author
John B. Benjamin is the owner of The WaterGardener which provides a wide selection of pond, Koi Fish and Water Garden supplies at wholesale prices, as well as valuable information on building and maintaining your pond. http://www.thewatergardener.com
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