Magnetic coupling pump

from Wikipedia, the free encyclopedia

A magnetic drive pump is the combination of conventional pump hydraulics with a mostly permanent magnetic drive system. This system uses the forces of attraction and repulsion between permanent magnets in both coupling halves for contactless and slip-free torque transmission. The containment can is located between the two coupling halves equipped with magnets, which separates the product area and the surrounding area.

Magnetic drive pumps are used in particular for poisonous, odorous or otherwise dangerous pumping media, as the containment shell keeps the medium hermetically sealed from the environment. Since the motor can still be freely selected, magnetic coupling pumps are usually cheaper than canned motor pumps , which also ensure the separation of the medium and the environment.

Constructive structure

The most important technical details of the magnetic drive pump are shown in the picture Structure of a magnetic drive pump (see below): The pump output is transferred from the drive shaft via the magnet driver (2) to the pump-side magnet carrier (3) without contact and slip. The magnet carrier is driving on the pump shaft (4) , the impeller (5) to. The pump shaft is mounted in a slide bearing (6) lubricated by the material to be conveyed . The containment shell (1) is located between the magnet driver and the magnet carrier ; it separates the conveyed material from the environment and is leak-free. The slide bearing and the magnetic coupling are lubricated or cooled by the delivery fluid of the pump, whereby the partial flow required for this is taken from a point of high pressure behind the impeller (7) or at the pressure port or is supplied by a separate supply, which runs through the elements to be cooled and exits again through holes in the impeller, inlet (on the suction side) or the separate feed.

Cross section of magnetic drive pump.jpg

Advantages of the magnetic coupling

In contrast to pumps with conventional mechanical seals, a magnetically coupled pump has the advantage of not requiring dynamic seals; only static seals are used. In contrast to the mechanical seals, these are mechanically less stressed and therefore much more wear-resistant and therefore generally completely maintenance-free. In addition, the inevitable leakage of small quantities of the pumped medium with mechanical seals can be avoided.

The complete encapsulation of the conveying medium from the environment is the main motivation to drive the immense construction and calculation and thus also cost expenditure, since this design represents in many cases the only possible technical solution.

disadvantage

If metallic containment shells are used (due to their chemical resistance they are often made of Hastelloy ), the rotating magnetic field induces eddy currents in these eddy currents, which convert the mechanical drive power into heat output of several kilowatts and thereby reduce the efficiency of the pump on the one hand and via the containment can on the other also heat the pumped medium. In the case of media with a steep vapor pressure curve - such as liquefied gases such as propane - frictional heat in the bearings as well as through the flowing medium itself can lead to evaporation of the same and thus cause bearing or other cavitation damage. Since the actual flow, pressure and thus temperature conditions in the containment shell cannot usually be measured, these are calculated or simulated using CFD , although there are high uncertainties due to the often insufficiently known surface roughness, flow channel dimensions and manufacturing tolerances, as well as numerical imponderables CFD modeling must be accepted. In order to reduce the risk of evaporation and thus the risk of pump damage, media with a steep vapor pressure curve u. a. Special containment shell designs have been designed that allow a less sensitive barrier medium to be fed into the containment shell or provide cooling.

The construction and design of the pump, its containment can and the magnetic coupling therefore require considerably more care and expertise than conventional pump types.

The induction of eddy currents can be greatly reduced or completely avoided by making the containment shell from a non-conductive material such as ceramic - e.g. zirconium dioxide - or plastic, but these materials are often expensive and are suitable for certain media, operating pressures or operating conditions (especially pressure surges ) Not.

Furthermore, the small gap dimensions in combination with the high flow mechanical effects in the containment shell prevent the conveyance of particle-laden media that could clog the narrow flow channels. For the same reason, often no non-Newtonian (rheological) fluids may be conveyed. In both cases, the use of a barrier medium can provide a remedy, provided that it is tolerable that the barrier medium is also partially conveyed, i.e. H. is mixed with the actual pumped medium.

Despite the disadvantages, the magnetic drive pump is in many cases the only solution for pumping particularly toxic, odor-intensive or expensive media without the need for a special motor ( canned motor ), which is why the high costs of this type of pump due to the enormous construction effort are justified and accepted.

Areas of application

The magnetic drive pump has advantages particularly when it comes to handling valuable or dangerous substances, as it reliably separates the product area from the environment, so that the risk of product leakage with any negative consequences associated therewith can be excluded. For these reasons, this type of pump is used in particular in the chemical and petrochemical industries.

Individual evidence

  1. ↑ Dr. Thomas Herbers, technical manager, Klaus Union: Magnetic coupling overload protection for gear pumps of the VPC and VPX series ( Memento of the original from October 15, 2013 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 234 kB), December 3, 1999. Accessed July 30, 2010. @1@ 2Template: Webachiv / IABot / www.variopumps.de

swell

Web links