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Industrial Pumps - Technical Articles
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TYPES OF MAGNETIC DRIVE PUMPS
Magnetic drive pumps belong to the category of hermetic pumps, such as those with jacketed motors, and have in common with these the operating principle. Both exploit a field magnetic to transmit motion to the impeller in the absence of contact with the outside of the pump and without the use of a mechanical seal (once stuffing box).
Their invention dates back to the 1960s, and is due to a German manufacturer which was the first to launch magnetically driven pumps onto the market they immediately had some success, since they were able to transmit powers of up to 30kW, which seemed enormous for the time.
The fact that these devices were very bulky and cumbersome, and that required a special centrifugal coupling joint to avoid breakages of polarity at start-up, reduced its success as the pumps were very expensive as well as cumbersome. Although the interest commercial and technical that these pumps had aroused had been large, the idea was quickly abandoned.
Modern technology, thanks to the introduction of new magnetic materials, has resolved the drawbacks that had impaired its development and in field of small-medium power magnetic drive pumps they can now compete on an equal footing with the more traditional sealed pumps mechanics, being able to boast, compared to the latter, the evident advantage of be perfectly airtight. This last factor proves to be crucial when choosing a pump intended to process toxic or dangerous liquids.
Let's try to better understand what magnetic drive is.
It is a transmission of power, without physical contact, between the driving machine and operating machine. It is a completely watertight system (i.e without mechanical seal) and the motion is transmitted via two magnetic rings coaxials mounted one on the motor shaft and the other on the impeller shaft. In a state of rest the 2 magnetic fields are in perfect balance with each other. However, as soon as a torque is applied to the "driving" nucleus, there is a disturbance this balance and the system, attempting to restore the magnetic balance, will respond by rotating the driven ring to which it is connected the operator tree.
A containment element is placed between the two magnetic elements
(called GLASS), which seals the pumping unit. The liquid is like this
confined inside the pump, without the possibility of emissions.
We will also call the motor ring the EXTERNAL MAGNET and the driven ring the INTERNAL MAGNET.
Modern magnetic couplings are of the synchronous type, i.e. characterized by the same rotation speed for both the driving shaft and the
duct; while the asynchronous type joints are composed of an aluminium-nickel cobalt magnetic core and a squirrel cage type rotor.
The latter are now technologically outdated, and modern magnetic couplings now use rare earth magnets.
The application of this technology has now established itself in various sectors industrial and can also be applied on plastic pumps. Among the various products found on the market are also accompanied by pumps for which There are real reference regulations. In the case of pumps intended for the chemical industry, the European reference standard is DIN-24256 substantially corresponding to the ISO-2858; the American one is ANSI-B73.1. Rubberplast supplies magnetic drive pumps compliant with DIN-24256, ISO-2858, ANSI-B73.1. These regulations establish dimensional and structural constraints. In the case of pumps for the refinery and petrochemical sector, the reference standard is API-685 which does not impose dimensional constraints but structural and functional. Rubberplast supplies magnetic drive pumps compliant with API-685.