The SCM-pumps are single or multistage, horizontal side-channel pumps in heavy duty design with end suction and vertical discharge flange. The pump shaft is driven via a permanent magnetic coupling. The static containment shell forms a closed system with hermetically sealed liquid end.
Suction- and pressure disks
The suction and pressure disks are sealed to the atmosphere by confined 0-rings, metal-to-metal fit, to prevent blowouts. In the shaft area, floating graphite impregnated PTFE-inserts are located for prevention of shaft deflection and seizing. The differential head is generated in the side-channel of the pressure disk.
The large diameter shaft is carried in slide bearings and has no deflection and only minimum torsional load. Thus, wear-free running of the impellers is ensured.
Since these pumps can handle relatively large amounts of gas, they are inherently self-priming as long as sufficient liquid remains in the pump. Therefore, the diffuser is also designed as a retaining stage. That means that the pump will still be filled with liquid after switch off and can be restarted without problem also in self-priming service.
The NPSH-conditions displayed on the next page are based on water at 20°C. When handling boiling liquids or hydrocarbons, the liquid level on suction side can be reduced to 50% of the published NPSH value.
Flameproof area features
Unlike "Canned motor" designs, the magnetic driven pump does not have electric windings adjacent to the fluid in the shroud and the magnet flux power transfer is non-sparking. Standard certified electric motors completely external from the pump housing are used, hence the possibility of flammable liquids contacting electrical windings is negligible.
The single elements of the multipolar magnetic coupling are manufactured of "Cobalt-Samarium Rare Earth", a permanent magnet material with unlimited life. The internal magnets are completely encapsulated; no contact with the liquid. 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 work as a synchronous coupling. The inner magnet ring transmits the required torque directly to the impeller. Overload of the magnetic coupling and slipping will not affect demagnetization. The magnetic drives are designed for electric motors, direct on line starting. Should a subsequent increase of motor power be required, the nominal power of the magnetic coupling can be increased accordingly by an additional series of magnets. The maximum transmissible power for SCM-couplings is 45 kW at 1450 rpm (60 HP at 1750 rpm).
When pump is in operation it generates eddy currents which heat up the conatinment shell and the product in the magnet area. This heat is dissipated by internal circulation. The circulation flow is led from discharge through the magnet area and the pump shaft to the suction disk of the last stage. Pressurizing of the containment shell prevents flashing of the liquid in the magnet end.
The major heat source of magnetic driven pumps is in the containment shell area which is cooled at normal running by the handled liquid. Nearly all malfunctions can be detected by monitoring the liquid temperature in the containment shell area. Installation of a temperature sensor therefore provides an optimum inexpensive form of continuous process protection. All pumps are provided with the required connections for RTD-elements.