What are Magnetic Drive Pumps? Benefits and ...

What is a magnetic drive pump?

Magnetic drive pumps, also known as mag pumps, are a type of centrifugal pump where the motor is coupled to the pump body with magnets instead of a direct mechanical shaft. This removes the need for a traditional sealing mechanism which eliminates leaks and makes mag drive pumps common choices in handling hazardous or corrosive liquids.

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Magnetic drive pumps are a good transfer solution with regards to leak prevention, maintenance requirements and the ability to handle corrosive, toxic, or flammable liquids. But much like standard centrifugal pumps, magnetic drive pumps are incompatible with many fluids. Furthermore, their magnetic mechanism can cause overheating and even alter the fluid&#;s composition. Electric diaphragm pumps address all of these issues while also providing more unique features to enhance the transfer process.

Disadvantages of magnetic drive pumps

While magnetic drive pumps eliminate the problems associated with mechanical seals, they have a number of limitations that make them less than ideal for a range of industrial applications. Graco solves this problem with QUANTM, an electric double diaphragm pump. Compared to a magnetic drive pump, QUANTM provides much more operational flexibility and control while solving many of the common issues associated with mag drive pumps.

• Unsatisfactory solution for abrasives and solids
  Magnetic drive pumps are primarily designed for pumping clean liquids that do not contain solids. Solids in the transfer material can cause quick failure of the close tolerance sleeve bearings and thrust surfaces inside the pump. These issues interfere with the pump&#;s performance and will accumulate, eventually causing complete failures of the pump and motor drive. Although some magnetic drive pumps are capable of moving heavier or more viscous fluids, they are best for applications that need to transport clean, low viscosity fluids. Ideally, they are not used for heavier applications that process solids containing fluids such as sludges, slurries and blends. QUANTM pumps are well suited to applications with varying flow and pressure. It poses no risk for shear-sensitive liquids and can easily handle abrasives and solids.
• Narrow preferred operating range and best efficiency point
  Magnetic drive pumps are just like their cousin, the centrifugal pumps, in that they have a specific impeller diameter, which means they only operate at optimal efficiency at a specific flow. And just like centrifugal pumps, the operating range is narrow. Not only will moving outside the preferred range significantly reduce the pump&#;s efficiency, but eventually, it causes cavitation, vibration, impeller damage, suction and discharge recirculation, or reduced bearing and seal life.
• Deposit because of magnet overheating
  The coupling action of the magnets can generate a lot of heat. Heat given off by surfaces warms the liquid in the pump and is passed into the process.  If the material is not evacuated efficiently, the heat may rise enough to bake constituents of the process liquid into the impeller magnet hub, resulting in build-up of a deposit and eventually catastrophic failure of the pump itself. Furthermore, the magnets in a magnetic drive pump can demagnetize when exposed to temperatures above their upper limit. Dry-running mag-drive pumps exacerbate and speeds up these types of premature failures in the pump system.
• Sensitivity in low flow or near shut-off head conditions
  Magnetic drive pumps are extremely sensitive when in low flow operation or near shut-off head conditions because the impeller is working against a higher head pressure. The magnetic coupling breakaway torque should not be exceeded. If this does occur, the magnetic coupling between the drive and the impeller axis is lost, causing the impeller to stop spinning, and damaging the pump or system.
• Sensitivity to variations in viscosity during operation
  Liquids can vary in viscosity based on temperature or chemical reactions. The viscosity of the pumped fluid affects the required input power and magnetic torque required for transfer. All magnetic couplings are rated for a maximum torque; beyond this point, the magnets operate at reduced speeds (decoupling). Operation in this state can permanently de-magnetize the magnets, making these pumps especially vulnerable to variable operating conditions and resulting in high power demands. The integration of power monitors into the process should be included in the total investment cost for this type of pump.
• Not self-priming
  Most centrifugal pumps are not self-priming. For the pump to work properly, its casing must be filled with liquid before start-up. When the casing fills with vapors or gases, the pump impeller becomes gas-bound and incapable of pumping. To make sure the pump remains primed and does not become gas-bound, centrifugal pumps need to be installed below the fluid level from which the pump takes its suction. Alternatively, the pump can be primed by supplying liquid under pressure through another pump placed in the suction line. QUANTM is self-priming and has excellent suction capabilities. With the added control of integrating an electric motor, every QUANTM pump includes a built-in AutoPrime feature for difficult to prime applications.
• Unable to run dry
  Because the pumped liquid acts as a lubricant and coolant, in the event of running dry, the bearing and some other pump head parts will overheat and eventually become damaged. They will then require service or replacement. Magnetic drive pumps should not be used in services and applications with a risk of running dry. QUANTM pumps can run dry indefinitely without causing any damage to the system, avoiding costly repairs.

Magnetic drive pump applications

• Chemical Industry
  While magnetic drive pumps are a common choice in the chemical industry for their leak-proof and seal-less design, QUANTM electric diaphragm pumps offer additional benefits. With the ability to handle a wider range of viscosities and being able to run dry, this makes them much more reliable for the continuous, demanding operation required in the chemical processing industry.
• Pharmaceutical Industry
  Magnetic drive pumps are frequently used in the pharmaceutical industry for transferring delicate fluids and medications. The sealed design helps to ensure product integrity and prevent contamination. QUANTM takes things a step further with its gentle pumping action to maintain the integrity of sensitive fluids without shear, which is important in the production of medications.
• Food and Beverage Industry
  Magnetic drive pumps are widely used for food and beverage processing applications. They provide a gentle handling of liquids, such as dairy products, beverages, and sauces. QUANTM pumps are designed to transfer shear-sensitive materials like dairy and sauces without altering their consistency or quality, going beyond the capabilities of mag drive pumps. They can also run dry without damaging the pump, which is a big advantage during food processing. The easy cleaning of QUANTM pumps also helps ensure the high hygienic needs of the food industry are met while still offering efficiency and reliability.

Summary of mag drive pumps vs electric diaphragm pumps

These are the QUANTM electric double diaphragm (EODD) pump benefits at a glance:

I want to address some common magnetic drive pump problems and concerns. Mag-drive pumps are very different from typical sealed pumps. Therefore, it is natural for people to have concerns. I narrowed the list to 8 questions that are commonly asked with regard to mag-drive pumps.

1. Won&#;t Dry Running Cause Catastrophic Damage to Mag Drive Pumps?

When a magnetic drive pump experiences an upset condition, specifically when it is starved of product, it does not necessarily mean that the pump is completely devoid of liquid. Most of the time, liquid remains in the pump to aid bearing lubrication during brief upset episodes and to prevent the bearings from breaking during brief dry-run periods. Taking it a step further, upgrading standard silicon carbide (SiC) bearings to enhanced SiC bearings with diamond-like coatings vastly increases bearing strength and decreases the coefficient of friction to 1/4 of that of standard SiC bearings.

2. Will Temperature Spikes Impact the Magnets of the Pump?

It is important to select proper magnet material relative to operating temperature considerations. Upset conditions can result in temperature excursions that impact the strength of the magnets, but a power monitoring device can minimize or eliminate this concern. When a mag-drive pump runs dry or against a closed discharge valve, the lower power drawn by the pump trips the monitor, shutting off the pump.

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3. What Happens When a Mag-Drive Pump Decouples?

If a mag-drive pump operates for a long time in a decoupled state, the magnets will be permanently demagnetized. However, the same power monitoring device that monitors the pump for temperature excursions also monitors for this condition as well. The design of mag-drive pumps do not make them particularly vulnerable to abnormal operating conditions. The power monitor addresses the concerns about increased capacity, specific gravity, and viscosity. Proper use of a power monitor eliminates many concerns.

4. Is Radial Loading Common with Mag Drive Pumps?

A major advantage of some mag-drive pumps is reduced radial loading compared with standard, seal-type overhung models. The straddle-mounted design with bearings on either side of the inner magnet provides excellent stability, reduces radial loading, and enables the pump to be more tolerant of off peak-operation.

5. What Does the Maintenance Schedule Look Like with a Mag-Drive Pump?

Mag-drive pump designs commonly offer an 8 to 10 year time table, sometimes more, without maintenance. One user discovered his mag-drive pump had operated 16 years without an outage. It did not fail at that point either &#; he took it down for preventative maintenance. Few sealed pumps in process applications operate so well.

6. Are Mag-Drive Pump Repairs more Expensive Than Sealed Pump Repairs?

The Sealed versus Sealless discussion has been one of great debate for a long time. But In failures of major proportions, this has some potential to be true. However, I submit that the frequent repairs, including replacement of often expensive seals over the life of a traditional sealed pump, would be more than the total cost of a major mag-drive repair. It should be added that major mag-drive failures are not particularly commonplace if some of the noted precautions (upgraded SiC bearings, proper magnet material, power monitors, etc) are implemented. Mag-drive pumps are good, cost-effective options for providing years of trouble-free operation in many pump applications, potentially saving pump users tens of thousands of dollars over the life of the equipment.

7. Can Mag-Drive Pumps Handle Toxic or Dangerous Process Fluids?

Mag-drive pumps can be very reliable in certain applications involving toxic and other dangerous process fluids including those that are corrosive, noxious, and high purity liquids. A mag-drive pump can definitely be solution to handling expensive fluids too; one sealed pump user reported that he was losing over $100,000 per year due to issues including leakage when handing a high-cost thermic oil used for heat transfer.

Less &#;dangerous&#; fluids can also be added to the list&#; including liquids that, when leaked onto the floor, could cause an employee to slip. A risk management department might find mag-drive pumps very attractive. Similarly, using mag-drive pumps to move process fluids with an objectionable odor can provide a much more pleasant working environment. 

8. Will Caustics Damage Internal Rotating Components in a Mag Drive Pump?

Mag-drive pumps can be configured to withstand cleaning from caustic agents. This is a powerful advantage in applications that use process food grade oils due to the need to subject the pump to regular cleaning. If your application requires regular cleaning, be sure to mention it to your pump manufacturer to ensure proper outfitting for this need.

Obviously, magnetic drive pump problems can easily be avoided. employing the preventative steps I discussed will almost certainly help keep your mag-drive pump running without issue. Although magnetic drive pumps are not the answer to every application, they can be an ideal solution across a broad range of applications when eliminating mechanical seals is desired. Magnetic drive pumps, when properly applied and operated, are the obvious choice for many applications.