General
Magnetic coupled DICKOW-Pumps of series NMB/NML are of sealless design.
The containment shell forms a closed system with hermetically sealed liquid end.
Applications
Magnetic driven NM-pumps are designed to improve plant and personnel safety, especially when handling toxic, explosive or other dangerous liquids which react on contact with the atmosphere. For all these services the containment shell replaces double acting mechanical seals with external fluid reservoirs and the necessary control equipment. NM-pumps therefore offer exceptional benefits to the chemical, petrochemical and allied industries and fulfill all environment protection regulations.
Maximum operating temperature 240°C (465°F) for the standard NMB/NML-type. The NMW-design with no internal circulation and dead-ended magnet end allows temperatures up to 350°C (660°F). The maximum allowable working pressure is 25 bar (364 psi).
Costruction
NMB/NML-pumps are single stage volute casing pumps with closed impellers, back-pull-out design, with end suction and top centerline discharge flange. Rigid support foot mounting is supplied as standard. Centerline mounted design is available on request. Capacity and flange to flange dimensions comply with EN 22858 (ISO 2858).
Design Features
Containment shell, Disassembly
The containment shell is designed as a pressure vessel to separate the pumpage from the atmosphere only. The containment shell is not used as an additional bearing holder.
No dynamic stress occurs. The containment shell is bolted to the bearing housing in a manner that allows removal of the bearing bracket (resp. of the drive motor at NMB-design) including outer magnets and ball bearings without exposing the pumped liquid to the atmosphere.
Magnetic coupling
The single elements of the multipolar magnetic coupling are manufactured of a permanent magnet material "Cobalt-Samarium - Rare Earth" with unlimited lifetime. The magnets in the internal rotor are completely encapsulated, no contact with liquid occurs.
Energy is transmitted to the hermetically sealed liquid end by a bank of external magnets passing motive force through the containment shell to a bank of internal magnets. Inner and outer magnet rings are locked together by magnetic power and are working as a synchronous coupling. The inner magnet ring transmits the required torque direct to the impeller.
Overload of the magnetic coupling and slipping will not effect demagnetization, if temperature is monitored by sufficient devices.
The magnetic drives are designed for electric motors, direct on line starting. Should a subsequent increase of motor power be required, i.e. when installing a larger impeller, the nominal power of coupling can be increased accordingly by an additional series of magnets.
The maximum drive power is 11,5 kW at 2900 min-1 (18,5 HP at 3500 min-1).
Internal clearances
The internal clearance between inner rotating magnets and containment shell depends on the wall thickness of the shell. However, a minimum clearance of 1 mm (0.040") will be provided in any case. This, together with wear resistant sleeve bearings, allows handling of fluid with solids.
Casing drain
Complete drainage of casing and magnet end is possible through casing drain. No additional drain required.
Outer ball bearings
The drive shaft of the NML-type is carried in generously dimensioned antifriction bearings, grease filled for life and protected by radial seal ring against environment.
At NMB-type, the drive magnet holder is keyed to the motor shaft, no additional ball bearings are available.
Containment shell protection
The different clearances between the rotating outer magnets and stationary containment shell, and the rotating magnet holder and bearing bracket respectively adapter, prevent rubbing of magnets on the containment shell in case of ball bearing failure.
Double sleeve bearings
The double internal bearings are of the sleeve type, positioned in the pumpage. The stationary bearings are located central in the common bearing housing that grants proper alignment for true running. Standard material is diamond coated pure Silicon Carbide, highly resistant against corrosion and wear and providing also dry running capability.
NPSH-Conditions
Due to the internal circulation from discharge to discharge, no elevated temperature will re-enter the impeller eye. Handling of boiling liquids is possible without an increase of NPSH-required.
Balanced thrust loads
The trust loads of the impellers are hydraulically balanced by impeller injection holes respectively the back vanes.
Monitoring
Connection for temperature detection element for containment shell surface temperature is available as standard. Dry running protection and monitoring of ball bearings and containment shell temperature with the patented "MAG-SAFE" System is highly recommended.
Internal circulation, pressurized magnet end
When pump is in operation it generates eddy currents which heat up the containment shell and the pumpage in the magnet area. This heat is dissipated by internal circulation. The internal circulation flows from discharge, direct behind the impeller, through the magnet area and the pump shaft back to the impeller respectively discharge side. Injection holes respectively back vanes in the rear impeller wall create forced circulation. The effect of pressurizing the magnet end with the sleeve bearings gives an additional safety marge against flashing when handling boiling liquids.
