Magnetically coupled pumps

Magnetically coupled pumps or pumps with magnetic drive, vary the style of traditional pumping, that the motor is coupled to the pump by magnetic means rather than by a direct mechanical shaft. The pump operates through a drive magnet, “conduct” of the pump rotor, which is magnetically coupled to the drive shaft driven  they are often used where a leak of the pumped fluid poses a great risk (for example, fluid aggressive. electric shock of chemical or nuclear, industry or – garden fountains). They have no direct link between the engine and the propeller shaft, so the gland is necessary. There is no risk of absconding, unless the enclosure is broken. Since the pump shaft is not supported by external bearings of the pump casing, press inside the pump is ensured by rings. The size of the pump of a magnetic drive pumps can range from a few watts of power from 1 MW to a giant. The construction consists of a metallic material and non-metal executions. MagDrive metal pumps are generally less effective than traditional pumps mechanical seals. The reason is a loss of power in the magnetic trasmission. This loss is called Eddy current and a magnetic drive pump can reach 20% and more of the installed power. This is due to the presence of the metal containment system in the magnetic field of emission. Latest innovation in technology of the pump drive magnetic effectiveness downplayed the absence, between pumps with magnetic drive and seals mechanical pumps. In some cases today there is more difference between this class of two pumps. In fact, the introduction of non-metallic containment shells reduced or eliminated the eddy currents generated in the coupling.

Below a summary of actually present materials on the market of the containment shell.

The comparison is based on a magnetic drive 18.5 kW installed centrifugal pump, turning at 2900 RPM.

Material / Technology Approx. Thickness [mm] Pressure Rating [bar] Temp. Field [°C] Magnetic Losses [kW] Comment
Hastelloy / other metallic alloys 1.2 – 1.7 PN 16 to PN 50 -90°C / +350°C 2.6 Most common, less efficient
Hybrid Containment shell 1.6 PN 50 -0.36 0.78 innovative
PEEK composite 3.5 – 5.5 3.5 – 5.5 -40°C / +120°C 0 High thickness, cost and temp. limits
Zirconium oxide 4-7 PN 16 -190°C / +350°C 0 High thickness, High cost
Borosilicate glass 3-7 PN 10 -40°C / +180°C 0 Weathering, high thickness, Pressure/Temp. limits

The only solution available on the market that can minimize Eddy current losses and keep metal hull in contact with pumped liquid is hybrid containment. This has a minimum of magnetic losses, but at high temperature and pressure resistance, for this reason most adapt at the request of heavy weight.

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