Magnetic Drive Pumps for Chemical Processing
The shaft seal is the part of a centrifugal pump most likely to fail. In chemical service, that failure means more than a repair ticket. A leaking acid, caustic, or solvent is a safety issue, a cleanup, and sometimes a reportable event.
Magnetic drive pumps take the shaft seal out of the design. Here’s how that works, where these pumps fit, and what to watch for once one is installed.
Why seals cause trouble
A conventional pump has a rotating shaft passing through a stationary casing, and a mechanical seal sits at that point. Seal faces wear. Chemicals attack the elastomers. Heat and misalignment shorten seal life. Even a well-chosen seal is a part you’ll eventually replace, and it tends to fail at inconvenient times.
Some fluids make it worse. Sodium hydroxide is a good example. We had a customer transferring it with a competitor’s sealed pump, and the seals were failing about once a month. Any fluid that reaches the seal area meets air, and sodium hydroxide crystallizes when it does. Those crystals build up at the seal faces and wear them out. A sealed pump struggles with this fluid because the seal is exactly where the fluid and the atmosphere meet.
We replaced those pumps with sealless mag drives. The fluid stays fully contained, so it never reaches air and never crystallizes. Those pumps have now been running for over 18 months without a seal to replace.
How a mag drive pump works
The motor turns an outer magnet assembly. An inner magnet assembly, attached to the impeller, sits on the other side of a non-magnetic containment shell. The magnets couple through the shell, so the impeller turns without a shaft ever passing through the casing.
That removes the dynamic seal. The shell and casing joints are static, which means far fewer places for process fluid to escape.
Where they fit
- Chemical transfer. Acids, caustics, solvents, and other reactive fluids in batch or continuous processes, especially where leakage can’t be tolerated.
- Water treatment and dosing. Sodium hypochlorite, ferric chloride, sodium hydroxide, sulfuric acid, and similar chemicals in municipal, industrial, and cooling tower programs.
Our mag drive pumps are built in 316 stainless steel, which handles organic solvents, moderate acids and alkalis, and elevated temperatures. We’ve run sealless pumps in services up to 350°F. For anything outside the common chemicals, check your fluid against our corrosion chart first, or send us the details and we’ll look at it with you.
Three things that shorten a mag drive pump’s life
Dry running. The internal bearings are lubricated by the pumped fluid. Lose prime or run without liquid and the bearings can be damaged in a short time. A flow switch, level sensor, or low-level cutoff costs little compared to the pump.
Low flow and heat. In a metallic containment shell, eddy currents generate heat. At very low flow there may not be enough fluid moving through to carry it away, and the fluid temperature can climb. Check that your minimum operating flow is high enough.
Decoupling. Every magnetic coupling has a torque limit. If system resistance goes past it, the magnets slip and the pump stops. That protects the motor, but it also tells you the pump wasn’t sized correctly for the full system curve. If a pump keeps decoupling, look at the system before replacing the pump.
Getting the selection right
Pump size, bearing material, and construction all depend on your fluid, temperature, and system. A short conversation up front is cheaper than a wrong pick. Send us your application details through the application request form or call 1-800-345-7867, and our team will review it and quote the right pump.
