Importance of torque and temperature in mag-drive pumps
We know that magnetic drive pumps are a great solution for applications where leakage is not an option, but they’re also well suited for maintaining a specific torque, or where temperature stability is important.
With these pumps, the impeller and pumped fluid are kept inside a sealed container. Magnets (a drive and driven magnet) are used to transfer the torque and power from the drive assembly to the impeller assembly.
The image below depicts the drive assembly in a rotating shaft magnetic drive pump:
Torque is transferred through the container due to these coupled magnets. The amount of torque depends on the gap between them. A larger gap allows a smaller torque and vice versa.
As these magnets are often made with rare earth alloys, pumps can be smaller and less complicated, with lower mass required to maintain a specific torque. However, it is useful to note that all magnetic couplings are rated with maximum torque capacity, beyond which they decouple and even permanently demagnetize if the pump continues to operate. A power monitor is useful for operating conditions that increase torque demand.
Another advantage of rare earth alloy magnets is greater temperature stability.
Magnetic drive creates heat from eddy currents between the two magnets. If the pump if exposed to temperatures higher than their upper limit, these magnets can lose strength and won’t be able to transfer the torque needed. If the torque required is greater than that which can be transferred, the magnets will decouple. The drive magnet will spin while the driven magnet is stationary, causing both to permanently demagnetize. Rare earth alloys that can handle temperatures up to 50 degrees Fahrenheit above maximum operating temperatures compensate for this issue.
As the inner magnet, pump shaft and bearing are immersed in the pumped fluid, they must be designed to operate efficiently in this environment. When liquids are highly viscous, for example, the pump may suffer from friction losses.
Liquids that are abrasive or corrosive can increase bearing wear. By choosing the right wetted materials – such as silicon carbide, thermoplastics, stainless steel and nickel alloys – magnetic drive pumps can handle hazardous, aggressive or corrosive fluids.
Clearly, magnetic drive centrifugal pumps can offer significant advantages, but they must be used correctly and adapted for process conditions. Issues with temperature and torque can be resolved by using rare-earth alloy magnets and the correct wetted materials.
If you’re considering implementing a centrifugal pump into your process, give us a call on 1-800-367-4180 (toll-free) to discuss the options available to you. We have experts on hand to help you choose, install, maintain, and monitor a variety of equipment. And to answer questions about things you’ve previously tried gone wrong.