How to Choose a Submersible Pond Pump
Magnetic Drive Pump :
The magnetic drive pump has been a mainstay in the aquarium and fountain making industry for decades. With advances in manufacturing technologies the true magnetic drive pump was introduced into the pond industry several years back and has enjoyed brisk sales from consumers. Its small size and price make them a good choice for fountain statuary or very small pond systems. A true magnetic drive pump can be identified by the following characteristics:
It contains an actual magnet at the core of its impeller assembly;
It has an impeller with straight or hinged paddles allowing it to spin in either direction;
The electrical motor is encapsulated in resin with the impeller assembly as only moving part;
Pump will consume very little power when operating;
Inexpensive purchase price.
In general you will find magnetic drive pumps from 40 GPH to about 3000 GPH flow. Advancing technologies have allowed for increases in flow but only to a certain point. The size and flow capacity of a magnetic drive pump are limited by the size of the actual magnet assembly. The magnet is made of a combination of rare earth materials. Up until the 1980’s this material was typically Alnico or Ferrite. At that time a new process was developed using Neodymium, which allowed a much stronger magnetic field and advances in manufacturing made the process affordable. The process of magnetizing this material leaves it ceramic- like and very brittle. In magnetic drive fountain and pond pumps you can identify a rare earth magnet by the resin or plastic sheathing placed over it for protection.
There are several pros and cons when using a magnetic drive pump:
The best benefit of magnetic drive pumps is the extremely low power consumption. Small pumps in the 40-200 GPH flow range often will consume only 2-10 watts. Larger magnetic drive pumps in the 1000-1300 GPH range average more towards 80-120 watts. Additionally these pumps are designed for continuous operation and will often last 5-7 years or more especially when run 24/7. Low purchase prices, extremely low operating costs, and the small sizes of these pumps make them a near perfect choice for statuary fountains and smaller water gardens.
Several drawbacks do exist for magnetic drive pumps and these prohibit them from meeting the needs of larger pond projects. With AC electricity (Alter-nating Current) the rotor changes directions each time power is applied to the magnetic drive pump. This changing rotation of the impeller means that it must be designed in a way that allows it to move water in either direction. This design restriction limits the practical size of pumps in the pond industry.
Demi Fortuna, a nationally recognized pond installer, pump expert, and consultant for Atlantic Water Gardens, indicates that the main drawback to more powerful magnetic drive pumps is this issue with directionality of the impeller. He explains that in order to make a larger flow magnetic drive pump one needs to increase the size of both the actual magnet rotor as well as the inefficient impeller. A larger impeller assembly means a hotter operating temperature as well as more strain on the impeller shaft upon starting. A hot magnet draws calcium deposits to it and with enough buildup on the rotor the pump will seize up.
Additionally, Demi states that impeller assemblies have a ceramic shaft on which they spin. The larger the magnet the more torque is placed upon the shaft upon each motor startup. Over time this torque creates stress upon the ceramic shaft until it finally snaps during a startup. A magnetic drive pump that is set in operation and remains running 24/7 will last many times longer than the same pump subjugated to frequent starts and stops.
Magnetic Drive Trends in the Pond Industry
In the last several years most manufacturers have seen the market potential of importing magnetic drive pumps under their company banner. Long time pump manufacturers like Danner Manufacturing have introduced various sized magnetic drive pumps at a lower price point for smaller consumer projects, hydroponic applications, and contractor installations of fountain statuary. Several other companies are moving into the small magnetic pump business including Easy Pro, Aquatop, Atlantic Water Gardens, and Anjon Manufacturing. They join long time established brands like Fountain Pro, Rio, and Alpine.
Pricing, while generally affordable, is increasing at this time. Shortages in the production of raw materials for the creation of the Neodymium based magnets have become an issue over the last two years. According to Steven Chu, in a December 2011 report titled “Critical Material Strategy,” which was prepared for the US Department of Energy, China holds 95% of the earth’s materials for Rare Earth magnets and they complete 76% of the world production of Neodymium magnets.
With increased pricing pressure from China and production shortages on these essential magnets the industry outlook appears to continue trending higher for these pumps. These price increases may be offset in part by the continued energy savings of the consumers who purchase them.
Direct Drive Pumps
Direct drive pumps have been the driving force and the contractors #1 choice for pond installations for many years. These powerful direct drive submersible pumps are capable of high working head heights and have been the workhorse of the pond industry. A direct drive pump can usually be identified by the following characteristics:
The pump impeller is attached to the motor with a drive shaft with only the impeller emerging from the pump motor body;
Pump will typically have a high working dynamic head (although low head direct drive pumps are available);
Pump allows passage of larger solid objects;
Pump impeller has curved vanes allowing for maximum flow and power;
Pricing varies pending quality of pump but is generally higher than the magnetic drive pumps.
Direct dive pumps are available from flow ranges of about 100 GPH to well over 12,000 GPH. Direct drive pumps contain inner seals that keep water from entering through the drive shaft inside the pump motor. The curved blades of the impeller maximize the flow of the water passing through and electrical consumption varies by pump according to size and manufacturer design. Direct drive pond pumps are most often used when a large volume of water is needed or flow is needed at greater heights than a magnetic drive can handle.
High flow capacity and capabilities of reaching higher waterfalls or features make the direct drive pump the continued choice by many professional installers. Better designs have created more energy efficient direct drive pumps although this varies by manufacturer. With typical pumps ranging from 1/5 HP (Horse Power) to 2 HP a wide variety of water features can be covered effectively. The direct drive nature of these pumps coupled with the impeller design allow for many solids to easily pass through without damaging the pump. Some direct drive pumps advertise the ability to pass up to 2? solids while 1 to 1.25? are the norm. Many manufacturers use double mechanical seals as this helps keep the water out and extends the life of the pump. On the higher end of these pumps they will often contain automatic shutoff switches to prevent overheating in the event of a low watersituation.
Mechanical seals are the weak point of direct drive pumps. If the seals leak water enters the electrical motor and the pump will short out and be ruined. Quality varies widely among the many direct drive pumps on the market and due diligence is required on the part of the pond professional in order to determine which will best meet the required application and the budget available. Some direct drive pump models have only single seals to protect the pump motor but most manufacturers have moved to at least double seals. Direct drive pumps are filled with a non-toxic oil that if it leaks into the pond is not a safety concern but is disturbing to consumers. Many so-called “oil free” pumps still contain some amounts of oil.
Electrical consumption on direct drive pumps also varies widely by size and even by manufacturer. Energy consumed can be as low as around 300 watts for a 1/2 HP pump to over 2000 watts for a 2 HP motor. According to Court Winegar and Art Hantla, of Fielding Pump Company, the installer or consumer can best select the most energy efficient direct drive pump by comparing the gallons per hour of flow generated per each Amp of the pump’s electrical rating.
Additionally Art and Court state that lubrication of the mechanical seals in a direct drive pump is the key to long lasting pumps. A seal extender, which splashes oil constantly to the uppermost seal, can greatly increase seal integrity and provide longer pump life. This device is built standard into the Shinmaywa line of pumps, which they represent.
Direct Drive Pump Trends in the Pond Industry
Costs of materials continue to climb for manufacturers resulting in increased wholesale and retail prices. Direct drive pumps are thought by many to have lost market share to the newer Hybrid pumps, which will be discussed next. However the manufacturers interviewed for this article contend that direct drive pump sales remain strong and given the limitations on alternative pumps the market is expected to be stable for many more years. Some manufacturers are reporting a strong year over last sales increase for direct drive pumps. Future advances to the direct drive pumps include the possibility of adding variable speed controls to further increase energy efficiency.
Magnetic Hybrid Pumps:
Seldom has a product emerged in any industry that is known by so many different names. The pumps in question are also known by the names Asynchronous, Magnetic Wet Rotor, Asynchronous Hybrid Magnetic Drive, Hybrid Pumps, Energy Saving Pumps, High Efficiency Pumps, and The New Mag Drive Pumps. All of these labels are in some way correct but have caused a great deal of confusion among new installers, retailers and consumers. These pumps are truly asynchronous, meaning that the impeller spins only in one direction like in a direct drive. This is different than the true magnetic drive pump which changes direction (synchronous) each time the pump is restarted.
The Magnetic Hybrid pump can be identified by the following characteristics:
A large curved vane impeller mounted on a rotor;
Impeller assembly rotor is not a magnet;
Total head is somewhat lower than comparable flow direct drive pumps;
Low energy consumption;
Typically available at a lower price than comparable flow direct drive pumps but higher than Magnetic drive pumps.
Unlike the rare earth magnetic drive pumps, which use an actual magnet, the hybrid only creates a magnetic field when the power is turned on. The impeller assembly is exposed to the water just like in the magnetic drive pump but in these pumps the rotor consists of a large steel or composite alloy (usually stainless steel) to which a curved vane impeller is attached for high pump output. By varying the size of the rotor and impeller the manufacturer can increase the GPH flow of the pump. The technology for these pumps has increased rapidly since their introduction to the pond industry a few short years ago. Flow rates have increased dramatically and you can now find these Hybrid Asynchronous pumps with flows between 800 GPH to an amazing 10,000 GPH.
The hybrid types of magnetic induction pumps are perfect for low and medium total dynamic heads. The impeller is similar to those on direct drive pumps as it will spin in only one direction increasing power and flow. According to Jon Lottes, President of Anjon Manufacturing, slightly larger pump housings have allowed for increased rotor and impeller sizes, which have increased the maximum flows up to 10,000 GPH and maximum heads to over 30 foot. Additionally Jon adds that larger rotor sizes mean a more efficient pump due to less slippage around the rotor.
The asynchronous Magnetic drive pumps are also very economical to operate with pumps in the 1,000 to 5,000 GPH running on between 100-400 watts. The larger pumps in the 6,000 to 10,000 GPH range will operate on average between 500 and 1000 watts.
In order to increase volume of flow and head pressure the manufacturers of these pumps have had to greatly reduce the space between the rotor and the rotor housing. The reduction of the space around the rotor means less slippage and more power but the extremely tight fit allows for very little water circulation or cooling of the rotor. Calcium deposits are attracted to the heated steel rotor and deposits can cause further circulation loss. While these hybrid pumps are generally very long lasting the primary cause of failure is seized rotors. Rotors are made of corrosion resistant stainless steel but Demi Fortuna of Atlantic Water Gardens adds that the Chromium molecules that retard the corrosion are often worn off the surface by heat and friction from small debris becoming trapped or calcium buildup. It is strongly recommended that the hybrid pumps be installed in a screened water environment to protect the pump from debris such as sand or grass clippings.
Head heights have increased steadily for the hybrid pumps but to date they still lag behind direct drive pumps. At this time their use is limited in tall waterfalls and other features with very high dynamic heads.
Hybrid Pump Market Trends
The future of these pumps looks extremely bright. Consumer awareness has made these the pumps of choice among many do it yourselfers. Market share for the magnetic hybrids is increasing steadily and the advancement of the technology is allowing greater flows and increased lifting capacity. Many installers who use a skimmer filter system are now selling and installing these pumps as an energy saving and economical alternative to direct drive pumps.
Costs are increasing for these pumps but new innovations are being devised to provide additional benefits and low cost features to the pumps. Future manufacturing will see energy saving Hi-LOW switches emerge on the market followed by full rheostat devices, which will allow users to lower the flow and the power consumption at will. Manufacturers are continuing to look at ways to better protect the steel rotor without diminishing capacity. Ideas include the possibility of encasing the rotor in plastic as is done with the smaller true magnetic drive pumps.
In conclusion, it should be noted that in general technology continues to advance the pump industry and our abilities to provide attractive and ever more economical water features to our customers. While there are professionals who choose to use only one type of pump for all their applications, many in our industry are enjoying the extreme versatility and features of the many different pumps available to us.