Magnet Coupling/containment Shell
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.
Outer and inner magnet, locked together by the magnetic field lines, are working as a synchronous coupling and transmit the required power to the pump shaft
The rated power of the magnetic coupling is determined such that no overload will occur through the whole performance range. Nominal coupling power and moments of inertia of the rotating components including driver are designed for direct-on-line start.
For reducing the eddy currents and improving the efficiency, a containment shell of "Sandwich design" is available
The inner pressurized shell consists of several centered rings. These rings are insulated from each other by confined gaskets and prevent occurring eddy currents.
This "low-loss" containment shell is recommended especially for driving power > 75 kW at speeds of 2900 and 3500 rpm.
The pump shaft is held in sleeve bearings. Bearing material is pure alpha grade Silicon Carbide. Pure SiC is suitable for general purposes, respectively for all kinds of liquids.
An additional diamond layer also tolerates short term dry running. The SiC-parts are shrink-fitted or elastically beared and thus, protected against strike and thermal stress. Design temperature is 250 ºC (482 ºF).
Internal Cooling Flow
When the pump is in operation, eddy currents are developed inside the metallic containment shells and converted into heat in the magnet area.
In order to avoid inadmissible temperature rise of the pumped fluid, this heat is dissipated through an internal cooling flow.
Suction and Discharge Casing
Suction and discharge casings are provided with sturdy cast feet for mounting on baseplates. HZMR-pumps have end suction and top discharge flanges.
When operating hermetically sealed pumps, cavitation must be avoided by all means. This applies especially for handling hydrocarbons, condensates and other low boiling liquids.
For lowest NPSH-values, the impeller of the first stage is designed as a suction impeller with enlarged impeller eye.
Balanced Thrust Loads
The thrust loads of the closed impellers are balanced by throttle gap and relief holes. The balancing of residual loads is effected by the balancing disk on pressure side.
The front side of the balancing disk is pressurized by the pump pressure p1. The rear disk side is connected with the pressure side of the first pump stage via an external auxiliary pipe. According to the rotor position and the adjusting gap S, a counter force is created by the differential pressure between front and rear side of the balancing disk. This counter force acts against the residual load towards the containment shell such that no thrust loads occur. No thrust bearings are required. The start-up rings keep the pump shaft in position during start-up and shut-off.
The drive shaft is carried in generously dimensioned oil-lubricated antifriction bearings. The bearings are rated for 25000 operating hours. The oil bath is protected against the atmosphere by a contactless labyrinth seal.
Oil level is controlled by constant level oiler. The oil chamber is sealed from the magnet chamber also by labyrinth seal.
The clearances between outer magnets and bearing bracket respectively containment shell are rated such that containment shell rupture in case of ball bearing failure is prevented.
Additional monitoring devices can be provided.
If desired, a mechanical stand-by seal can be supplied in lieu of the inboard labyrinth seal. This mechanical seal separates the magnet area from the oil bath respectively from the atmosphere and forms, together with the closed bearing bracket lantern, a secondary containment behind the containment shell.