What types of submersible pumps are there, and what's the difference?

by: Demi Fortuna

The first submersible pumps used for water gardens in this country, Direct Drives, were originally developed for sump and sewage duty, and are still a favorite of contractors for their strength and durability. These pumps are called Direct Drives because the impeller is directly connected to the electric motor via a shaft. The impeller has to be in the water, and the motor has to stay dry, so the shaft needs to have seals, usually two or three, that keep the water out of the motor. The seals have to work whether the motor is running or stopped, hot or cold, and the impellers are typically heavy, so the motor has to be strong enough to overcome the resistance of the seals and impeller, and that takes power, which costs money. Still, if you need a pump that can chop through algae, or can pump to very high heads, Direct Drives are the way to go. Atlantic 315 Tidalwave Pump

If you don't need high head capacity, you can save operating costs by lightening the impeller and eliminating the seals, and that's exactly what Magnetic Drive pumps do. Imagine taking a 'doughnut' of copper wire and 'frosting' it with a waterproof icing. If you suspend a magnet inside that doughnut and connect the coil to power, the magnet will spin, by magnetic induction. Attach an impeller to the magnet and presto! You have a Mag Drive. The pros are: there are no seals to deal with; energy consumption can be very modest and the simple impeller is easy to replace. On the other hand, Mag Drives don't have the power to produce a lot of flow or head pressure, so they're mainly useful in smaller ponds, under 500 gallons. One other quirk -- that magnet that spins when the coil is energized? Well, you never know which direction it's going to turn on startup, so the impeller has to be able to work in either direction. If you can get the magnet to spin in only one direction, you can make a more efficient impeller and… enter the Asynchronous Hybrid Magnetic Drives.

Pondmaster Mag Drive Pump - 700 GPH

By figuring out how to make the impeller spin in only one direction (so-called "asynchronous" rotation) you can combine the magnetic induction of the Mag Drives with the efficient, one-way impeller of the Direct Drives. The Asynchronous Hybrid Magnetic Drive pump combines the efficiency of the Mags with higher flows and head pressures of the Direct Drives, and have become the mainstay of the industry. 'Asynchs' excel at providing flows up to 6000 GPH, to heads up to 30 feet, at very low wattages compared to the other types of pumps. The catch this time? The high efficiency requires close tolerances inside these pumps, which makes them susceptible to clogging and scale buildup. They need to have good prefilters to keep debris out, and regular cleaning where lime scale and other water deposits are a problem.

Pondmaster HY-Drive 6000