A magnetic drive pump’s main feature is that the pump shaft is driven through a non-contact coupling between internal and external magnets to transport liquids.
Principle of Magnetic Drive Pumps
When the electric motor starts, it drives the outer magnetic rotor to rotate, creating a rotating magnetic field. The rotating field of the external magnets interacts with the internal magnets, forming magnetic coupling and transferring driving force to the internal magnets.
Due to magnetic attraction, the internal magnets rotate synchronously with the external magnets. Since the internal magnets are connected to the impeller, the impeller begins to rotate. The rotating impeller generates centrifugal force, drawing liquid from the inlet into the pump body and discharging it through the pressure chamber to the outlet.
Types of Magnetic Drive Pumps
Based on magnetic drive methods, they can be classified into synchronous or asynchronous magnetic drive pumps.
| Synchronous magnetic drive pumps: Most magnetic pumps use a synchronous design. The motor is connected to the outer magnet cylinder through an external coupling, while the impeller is connected to the inner magnet cylinder. A fully sealed isolation sleeve completely separates the outer and inner magnet cylinders, keeping the inner magnet cylinder in the medium. The motor shaft directly drives the impeller through magnetic pole attraction between the cylinders.
| Asynchronous magnetic drive pumps: Use a cage-structured torque ring instead of an inner magnet cylinder. The torque ring, similar to an asynchronous motor’s rotor, generates induced EMF and a magnetic field in the outer magnet cylinder’s rotating field, rotating at a slightly lower speed. Without permanent magnets in the inner cylinder, it can operate at higher temperatures than synchronous drives.
Magnetic Components in Magnetic Drive Pumps
The main magnetic components are the internal and external magnetic rotors.
| Internal magnetic rotor: Connected to the impeller, made of permanent magnetic materials. It interacts with the outer magnetic rotor through magnetic fields for synchronous rotation.
| External magnetic rotor: It is connected to the motor. When motor-driven, it drives the inner magnetic rotor through magnetic fields.
Types of Magnets Used
Neodymium Magnets
| Performance: Magnetic energy product reaches 35,000-45,000 Gs, with potential for improvement through formula modifications.
| Grade: Grade 38SH neodymium magnets are commonly used in stainless steel magnetic drive pumps.
| Temperature: Generally operates at 80°C, but can reach 200°C with improved formulas and processes.
| Price: More expensive than ferrite magnets but offers superior magnetic properties, making them widely used in magnetic drive pumps.
Ferrite Magnets
| Performance: Magnetic energy product typically reaches 12,000-16,000 Gs after saturation magnetization.
| Temperature: Theoretical temperature resistance of 250°C, with reversible magnetic demagnetization at high temperatures.
| Price: Ferrite magnets are cost-effective compared to other magnetic materials, but limited by energy product, especially unsuitable for high-density media.
Magnet Design
| Quantity
Even numbers of magnet pairs are arranged systematically on inner and outer magnetic rotors to form complete coupling systems.
| Arrangement
When opposite poles face each other (displacement angle Φ=0), the magnetic system energy is low
When like poles face each other (displacement angle Φ=2π/n), the magnetic system energy is high.
Measures to Maintain Magnet Performance in Magnetic Drive Pumps
Preventing demagnetization is key to maintaining the performance of magnets in magnetic drive pumps.
| Isolation Sleeve: During the operation of a magnetic pump, the isolation sleeve is subjected to an alternating magnetic field, which induces eddy currents. These eddy currents reduce transmission efficiency and convert it into heat. Therefore, the design of the isolation sleeve must carefully consider the choice of materials and their geometric dimensions.
For metal isolation sleeves, Hastelloy, titanium alloys, or austenitic stainless steel should be used. The thickness is generally between 1.0 to 1.2 mm.
For low-power magnetic drive pumps operating at lower temperatures, non-metallic materials such as plastic or ceramic can also be considered for the isolation sleeve.
| Operate within Specified Temperature Conditions: It is strictly prohibited to exceed the specified medium temperature. The ambient temperature during pump operation should be below 40°C, and the motor temperature rise should not exceed 75°C. A platinum resistance temperature sensor can be installed on the outer surface of the isolation sleeve to monitor the temperature rise in the clearance area.
| Proper Magnetic Torque Design: When selecting a magnetic pump, the design magnetic torque should not be too low to prevent excessive temperature rise due to overload conditions.
Applications
Magnetic drive pumps are widely used in industries requiring high safety and leak-free operation:
| Chemical industry: For corrosive media like acids, bases, and salts.
| Pharmaceutical industry: For sterile, leak-free transfer of pharmaceutical liquids.
| Food industry: For food-grade media like juices and milk, ensuring contamination-free transfer.
Magnetic Drive Pumps Manufacturer
At Tengye, we’re thrilled to be early participants in your new projects. Our passion for magnets extends from material selection and design optimization to providing magnetic solutions. We hope to bring our knowledge and experience to the forefront by actively engaging in your upcoming projects. Work with our magnet experts to get the right magnet solution.
Image Source: Andersonprocess & Arbo-pumps & Dienerprecisionpumps & Magnetictech & Ruhrpumpen
