Magnetically Coupled Pumps vs. Mechanical Seals and Canned Motors
If you work in chemical process industries (CPI), specifically with pumped media that has a moderate to high hazard potential, you’ll likely use one of the following sealing systems:
- Double mechanical seals (liquid-sealed or gas-sealed)
- Canned motors
- Magnetic coupling
Mechanical seals that are liquid-sealed are used fairly frequently, despite disadvantages, including a highly complex sealing system that can result in high maintenance costs. Gas-sealed mechanical seals are good for simple gas, particularly in vertical pumps, and tend to have lower operating/maintenance costs. However, when you consider operation, maintenance, and safety, canned motors and magnetic couplings are really the only efficient choices — here’s why:
Airtight Seals: Hermetically Sealed
A pump system with canned motors or magnetic couplings is airtight. What happens is, a rotating magnetic field transfers torque (rotation) through a thin metallic wall to the pump shaft. Now, in a canned motor pump, the pump and motor are essentially one unit with a rotor and impeller on a single shaft. This means that the canned motor pump doesn’t function independently of the pumping medium, which could be a disadvantage. Another downfall if you’re pumping gas-laden or magnetizable media and solids as you might need to implement additional steps to your process, like external flushing.
Finally, from the perspective of energy efficiency, the canned motor is becoming increasingly obsolete as over 30% of drive energy is lost due to heat generation. This method could also unintentionally heat the media you’re pumping.
The Magnetic Option
On the other hand, a magnetically coupled pump’s motor is not the pumping medium. In most designs, the motor shaft will carry an external magnet rotor, shifting magnetic force through a metallic wall to an internal magnet motor. Rings of permanent magnets (rotor) are arranged on the drive and pump shafts — typically samarium-cobalt or neodymium, which we offer at Apex. The motor turns the shaft and one set of magnetics, which generates a field to turn the second set, thus powering the impeller.
Fortunately, the heat transmission into the pumping medium is significantly lower compared to canned motor pumps, meaning you don’t run the risk of unintentionally heating your media. Also, unlike double-mechanical seals, this option is just as effective in horizontal pumps as in vertical pumps.
Overall, and especially for mild to moderately risky gas and liquids, magnetically coupled pumps are the way to go. They balance the best of what pumps can offer including lower maintenance/operating costs and higher levels of safety.
Ultimately, the type of magnet you use in your magnetically coupled pumps depends on the type of media you’re pumping. It will determine things like whether or not you want to add a specific coating to your magnet. If you want to purchase Apex Magnets for your magnetic coupling, have all this information on hand when you browse our collection or fill out a custom form fill. And remember, if you have questions, we have answers. Contact us anytime at (1-304) 257-1193.