Magnetic pump with mechanical seal

Abstract

Magnetic pump with pump chamber and drive area with containment shell, characterized in that at least one mechanical seal (GLRD, 3) is arranged between the pump chamber (2) and the magnetic drive / bearing (10, 13).

Description

[0001] The invention relates to magnetic pumps. Conventional pumps (non-magnetic pumps) are generally sealed by mechanical seals. Mechanical seals are usually not completely leak-proof, so that pumped fluids, even if only in small quantities, can escape into the environment. To prevent this, mechanical seals have been largely eliminated from pumps and replaced by a magnetic drive design. Thus, pumps with a magnetic drive (so-called magnetic pumps) have been increasingly used.

[0002] In magnetic pumps, the pumped medium is hermetically sealed from the environment, preventing any leakage. Magnetic pumps are therefore used wherever the following media must not be released into the environment: - Toxic media - Odor-intensive media - Dangerous media - Expensive media - Media that react with the surrounding air.

[0003] Various magnetic pump designs exist in the prior art, but they all essentially share the following design features: 1. All functional areas (pump chamber, storage chamber, and inner magnet carrier chamber) are interconnected, so that the pumped medium, which is only intended to be pumped, also lubricates the plain bearings and cools the magnet carrier. In most cases, however, the pumped media have no or only insufficient lubricating properties that would be necessary for the reliable operation of the plain bearings and to achieve a long service life. 2. The pump impeller is connected to the rotating, driven magnet carrier via a shaft. The shaft is guided in plain bearings, both radially and axially. Ceramic roller bearings are used in very rare cases. 3. From a point of high pressure inside the pump, bores and gaps lead through which the medium flows to the sliding bearings and the gap between the inner magnet carrier and the containment shell to lubricate and cool these areas. 4. The drive magnet carrier is located outside the media housing. The torque is transmitted through the housing wall of the containment shell by the magnetic forces and thus drives the pump via the driven magnet carrier. 5. The drive magnet carrier is guided in external rolling bearings (with coupling in pump versions) or, in block design, directly connected to the shaft of the drive motor.

[0004] If metallic containment shells (often made of Hastelloy due to its chemical resistance) are used, the rotating magnetic field induces eddy currents within them. These currents convert the mechanical drive power into heat, often several kilowatts, thereby reducing the pump's efficiency and heating the pumped medium via the containment shell. Frictional heat in the bearings, as well as heat from the flowing medium itself, can, in the case of media with a steep vapor pressure curve—such as liquefied gases like propane—lead to vaporization if the design is not carefully considered, potentially causing bearing damage or other cavitation-related problems.Since the actual flow, pressure, and thus temperature conditions within the containment vessel cannot usually be measured, they are calculated or simulated using CFD. However, this involves significant uncertainties due to the often insufficiently detailed knowledge of surface roughness, flow channel dimensions, and manufacturing tolerances, as well as numerical imponderables inherent in CFD modeling. To reduce the risk of evaporation and thus pump damage, special containment vessel designs are developed for media with steep vapor pressure curves. These designs allow for the introduction of a less sensitive barrier medium into the containment vessel or incorporate cooling.

[0005] The design and construction of the pump, its containment shell, and the magnetic coupling therefore require significantly more care and expertise than conventional pump types. The induction of eddy currents can be greatly reduced or completely avoided by manufacturing the containment shell from a non-conductive material such as ceramic – for example, zirconium dioxide – or plastic; however, these materials are often expensive and unsuitable for some pumped media, operating pressures, or operating conditions (especially pressure surges).

[0006] Furthermore, the small gap dimensions, in combination with the high fluid dynamics within the cavity, prevent the pumping of particle-laden media that could clog the narrow flow channels. For the same reason, non-Newtonian (rheological) fluids are often also prohibited from being pumped. In both cases, the use of a barrier fluid can remedy this, provided it is acceptable that the barrier fluid is partially pumped along with the actual pumped medium.

[0007] Despite its disadvantages, the magnetic coupling pump is in many cases the only solution for pumping particularly toxic, odorous or expensive media without needing a special motor (split tube motor), which is why the high costs of this type of pump, resulting from the enormous design effort, are justified and accepted.

[0008] Based on this prior art, the invention aims to significantly improve a magnetic pump of the type mentioned above and to design it in such a way as to avoid all the disadvantages of conventional magnetic pumps. The invention achieves this problem through the characterizing features of claim 1.

[0009] By using the arrangement according to the invention of at least one mechanical seal between the pump chamber and the magnetic drive / bearing, all the aforementioned disadvantages of conventional magnetic pumps can be avoided altogether.

[0010] The pumped medium is held in the pump chamber 2 by the product-side, first mechanical seal (GLRD 3) and thus separated from the bearings 11, 8 and the magnetic drive 10. Solid-containing or highly viscous media therefore do not enter the shaft bearings or the gaps 19 of the containment shell with magnetic drive 10. Clogging by particle-laden media is prevented because the medium cannot enter the narrow flow channels of the magnetic drive or the bearings.

[0011] Between the first and second GLRD 6 is the barrier fluid chamber 4, which provides an additional barrier to the pumped medium. The product-compatible, clean barrier fluid circulates in circuit A, B through an integrated pump unit 4 and a barrier fluid reservoir, where the barrier fluid can be individually cooled or heated. Furthermore, the barrier fluid chamber can be pressurized to ensure optimal operating conditions at GLRD 3, 6. Pressureless operation of the GLRD is also possible. The barrier fluid chamber can also be monitored and controlled for pressure, temperature, and leaks. The second GLRD 6 separates the barrier fluid chamber A, B from the storage and magnetic drive chambers D, E.

[0012] By placing a double GLRD 3, 6 at this point according to the invention, the drive shaft can be guided without play in conventional precision bearings, free from the pump medium. The rolling bearings 11, 8 can thus be operated with a low-viscosity oil as intended. This oil also flows in a circuit via an integrated pump device 13 through the inner magnetic drive 10 and containment shell 12 to an oil cooler and from there back to the pump bearing chamber.

[0013] When using a non-metallic containment shell, a cooling device for the oil circuit is unnecessary due to the absence of heating from eddy current losses in the magnetic drive. For low-temperature fluids, grease-lubricated precision bearings can be used instead of oil lubrication. The oil-filled bearing / magnet carrier chamber can also be monitored for pressure or temperature.

[0014] Because the pumped medium is separated from the magnetic or bearing chamber by the mechanical seal, vaporization cannot occur with media that have a steep vapor pressure curve, thus preventing bearing or other cavitation damage. Therefore, no special containment shell designs are necessary. Due to the design of the magnetic pump according to the invention, media containing solid particles, e.g., 2 mm in size and 30% by volume, can be pumped. With a suitable pump design, even larger particles can be pumped.

[0015] The delivery pressure of the new magnetic pump is no longer determined by the design or material of the containment shell (generally max. 10 bar) but by the design of the mechanical seal (25 bar in the standard version). With the use of special mechanical seals, media with significantly higher pressures can also be pumped.

[0016] Pressure surges from the conveying chamber never reach the containment vessel, thus preventing deformation (in the case of metallic containment vessels) or breakage (in the case of ceramic containment vessels). Slide bearing failure is also impossible, as there are no slide bearings.

[0017] No external flushing or internal solids filters are required. No unwanted heat is transferred to the pumped medium via the magnetic coupling, especially with metallic containment shells. Furthermore, there is no shearing effect or other fluid dynamic influence on the medium from the sliding bearing and containment shell, because the medium does not enter this area.

[0018] The pump according to the invention can also pump non-Newtonian (rheological) fluids.

[0019] The pump will not run dry, as the barrier fluid chamber between the two mechanical seals and the oil-filled bearing chamber are self-venting. This means the pump will not run dry even if there is little or no fluid in it. The pump can also be operated in partial load mode (e.g., at a significantly reduced speed in bypass mode) without time limits and without overheating. This makes repairs to the system flexible and safe.

[0020] The invention can be used in the following machines: centrifugal pumps, gear pumps, rotary piston pumps, screw spindle pumps, agitators, canned motor pumps, aeration or deaeration machines / fans, bead mills, and in all machines where a rotating shaft needs to be sealed to the housing, e.g., compressors and vacuum pumps.

[0021] The following double sealing arrangements can be used: - Concentric mechanical seals - Tandem mechanical seal - Back to Back mechanical seals - Face to face mechanical seals - Instead of a double mechanical seal, a single mechanical seal can also be used, depending on the required safety level and control requirements.

[0022] Instead of a double mechanical seal, multiple mechanical seals, also known as special mechanical seals, can be used, depending on the safety level and control requirements. These involve connecting three, four, or more mechanical seals in series to dissipate any pressure leaks that may occur. The number of mechanical seals depends on the amount of media pressure to be dissipated and the safety requirements.

[0023] Fears that the use of a single or double GLRD according to the invention at this point will revive the well-known problems of conventional pumps are completely unfounded.

[0024] In contrast to conventional pumps, in the pump according to the invention, the first product-side GLRD 3 is positioned directly behind the pump impeller 2 in an open product chamber. Any solids present in the medium are conveyed away from the GLRD 3 and into the pump chamber by the centrifugal forces of the rotating impeller 2. This allows the shaft bearing 8, 11 to be positioned very close to the impeller, directly behind the GLRD 6, even in a double GLRD configuration. The very short distance between the impeller 2 and the bearing 8, 11 prevents excessive shaft deflection across the impeller 2 due to the hydraulic back pressure building up on the pump's pressure side. This largely prevents undesirable radial movement between the GLRDs and thus extends their service life.

[0025] Furthermore, in conventional pumps, the sealing rings always seal the pumped medium (in the case of a single sealing ring) or the pumped medium and the barrier fluid against the atmosphere. Most premature sealing ring failures are caused by latent or absolute dry running of the atmospheric sealing ring (especially in the case of double sealing rings), e.g., due to barrier fluid loss, insufficient cooling of the sealing ring, or vaporization of the barrier fluid (which is practically equivalent to dry running).

[0026] This cannot happen with the GLRD (sealing barrier fluid) used according to the invention. All GLRDs are wet-running, meaning there are practically no GLRDs exposed to the atmosphere. In the product-side GLRD 3, the medium is on one side and the barrier fluid on the other. In the second GLRD 6, the barrier fluid is on one side and the oil on the other. Dry running is therefore virtually impossible. In this arrangement, appropriately designed GLRDs run longer than the rolling bearings. Thus, the GLRDs are no longer the problem, as they are in conventional pump applications.

[0027] The significantly longer service life and the increased operational reliability through individual control of the individual functional areas compensate for the higher costs through significantly greater efficiency.

[0028] The measures and embodiments according to the invention are not limited to the embodiment shown in the drawing. The respective design is left to the discretion of the person skilled in the art to adapt to specific uses. Reference symbol list A Cooling barrier fluid chamber IN B Cooling barrier fluid compartment OUT D Cooling Magnetic coupling / lubrication Storage space IN E Cooling Magnetic coupling / lubrication Storage area OUT 1 spiral casing 2 impeller with pump shaft 3 GLRD product space sealing 4 Cooling recirculation system 5 GLRD housings 6 GLRD storage room sealing 7 Housing storage 8 bearings 9 magnets on the outside with drive shaft 10 internal magnets, driven magnet carrier 11 warehouses 12 Split pot 13 Circulation device Cooling bearing / magnetic drive 14 Bearing seal 15 warehouses 16 Cooling circulation system 17 warehouses 18 Bearing seal 19 Oil room

Claims

[1] Magnetic pump with pump chamber and drive area with containment shell, characterized by , that at least one mechanical seal (GLRD, 3) is arranged between the pump chamber (2) and the magnetic drive / bearing (10, 13). [2] Magnetic pump according to claim 1, characterized by , that the functional areas pump and magnetic drive are separated by at least two GLRDs (3, 6) and thus enable the intended operation / control of the different functional areas, resulting in three different, separate functional spaces: a) Pump chamber with impeller (2) in the spiral casing (1) b) Barrier fluid space (4) between the GLRDs (3, 6) c) Storage or magnet carrier space (10, 13). [3] Magnetic pump according to claim 1 or 2, characterized by , that the following double sealing arrangements are used: • Concentric mechanical seals • Tandem mechanical seal • Back to back mechanical seals • Face to face mechanical seals. [4] Magnetic pump according to claim 1, 2 or 3, characterized by , that at very high media pressures multiple GLRDs are used connected in series.

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