Pumps are often divided into two types:
traditional sealed pumps and sealless pumps. Pumps that require a sealed system, usually in the form of a mechanical seal, fall into the first category. The second category comprises all types and models of seal-less pumps, which do not need to be sealed. Magnetic-driven pumps are one of the most common types of sealless pumps.
They’re employed in situations where leaks aren’t acceptable or liquids are tough to seal. Magnetic drive pumps, also known as magnetically coupled pumps, differ from ordinary pumps in that the electric motor (the driver) is magnetically attached to the pump rather than via a direct mechanical shaft.
The pump is powered by a driving magnet, which eliminates the need for shaft sealing. This is a significant benefit. Magnetic drive pumps, on the other hand, are not suitable for all applications and have power rating limitations. The characteristics, advantages, and disadvantages of magnetic drive pumps in processing facilities are discussed in this article.
Magnetic drive pumps
When aggressive or dangerous liquids, exotic materials, acids, alkalis, corrosives, pollutants, and toxins are pumped, magnetic drive pumps are frequently used. They’re also utilized for ultra-pure liquids and liquids that are difficult to seal. To prevent hazardous/challenging liquids from escaping to the atmosphere, sealed pumps used in these types of services may leak over time or require complicated, expensive double seals, which can result in safety issues, downtime, and higher maintenance costs.
Difficult liquids are another major application for magnetic drive pumps; for example, some liquids can crystallize on seal faces, resulting in seal failures. A permanent flush system should be run to the seal to avoid this. However, this can raise maintenance costs, seal flushing liquids, and energy use. A magnetic drive pump is a better choice for these tough services.
Because there is no direct connection between the electric motor shaft and the impeller in magnetic drive pumps, no seal is required. Unless the pump casing is cracked, there is little chance of leakage. Pump excursions and unplanned shutdowns are known to be caused by seals. Obviously, the removal of seals improves the performance, reliability, and availability of pumps significantly. Liquids can be pumped without spilling because the risk of leakage is fully avoided. Eliminating the seals also eliminates the friction loss, wear, expenses, and noise that come with them. This allows for total separation of the liquid from the pump drive and improved motor power transfer to the pump.
Magnetic drive pumps are available in a wide range of materials and metallurgies, both metallic and nonmetallic. Pumps with polymer linings are also employed because they are more corrosion resistant. Polytetrafluoroethylene (PTFE), perfluoroalkoxy alkanes (PFA), and polyvinylidene fluoride are some of the polymer coating alternatives (PVDF). These lined or non-metallic choices are typically used for normal temperatures, which are generally less than 90°C. For even higher temperatures, metallic magnetic drive pumps have been employed.
Bearings for magnetic drive pumps
Because a magnetic drive pump is an enclosed piece of machinery, bearings cannot be lubricated with oil or grease. As a result, pumped liquid is utilised to lubricate bearings as well as to cool them. A portion of the pumped liquid is frequently withdrawn from the pump’s discharge; this flow is known as recirculation flow and is used to cool the magnetic system, lubricate radial and thrust bearings, and other similar applications that require lubricant or cooling fluid.
Magnet drive pumps are frequently equipped with “sleeve bearings,” which lubricate themselves using the pushed liquid. A sleeve bearing is the most basic type of bearing, with only bearing surfaces and no rolling parts. As a result, the sleeve or journal glides across the bearing surface, which is lubricated with pumping liquid. In comparison to many rolling-element bearings, these bearings are compact and lightweight, have a high load-carrying capability, and have a longer life. The materials used in its construction, as well as the needed clearances between the sliding surfaces, may limit the liquids and services that this type of pump can handle.
Disadvantages and limitations
There are some restrictions with magnetic drive pumps since they employ magnets to deliver torque and power from the drive assembly to the impeller assembly. Magnet materials, for example, can lose their magnetic when exposed to temperatures above their threshold. As a result, the temperature characteristics of each service are crucial. The magnetic connection loses some energy. The reason for this is due to certain magnetic resistance. A typical magnetic drive pump is typically less efficient than standard centrifugal pumps as a result of this and other factors.
Because an extremely big or powerful magnetic connection is not possible nor cost-effective, there are some constraints in power rating. Limitations in power and torque should always be taken into account while choosing these pumps.
The risk of running dry is one of the biggest drawbacks of magnetic drive pumps. In the event of a dry run, the bearing and some other elements may overheat and eventually become damaged since the pumped liquid will act as lubrication and coolant. Magnetic drive pumps should not be used in services or applications where there is a risk of dry running.