SCM Details

General

Type SCM is a magnetic driven multistage, self priming horizontal side-channel pump. The side-channel pump with its high differential head has the advantage of operating more economically than normal centrifugal pumps for low capacity and high head applications. Side-channel pumps are suitable for solving many pumping problems in the chemical and petrochemical process industries. The SCM-pump is a heavy-duty sealless magnetic driven unit for handling clean liquids free from solids and is designed to improve plant and personnel safety, especially when handling toxic, explosive or other dangerous liquids which react on contact with the atmosphere. The static shroud (containment shell) replaces the requirement for double mechanical seals with external fluid reservoirs or barrier fluid circulating systems. Due to the fact that 90% of pump failures and repair requirements are caused by leaking mechanical seals, the sealless design saves considerable maintenance and spare parts costs. The maximum allowable working pressure is 600 PSI and maximum temperature is 240 degrees C.

Construction

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 shroud 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 O-rings, metal to metal fit, to prevent blowouts. In the shaft area, floating graphite impregnated PTFE-inserts are located for prevention of shaft deflection. The differential head is generated in the side-channel of the pressure disk.

Side-channel impellers

The star-shaped side-channel impellers are rotating between the suction and pressure disks in a floating position on the pump shaft. No hydraulic thrust loads exist. Torque transmission between shaft and impeller is by keys.

Pump shaft

The large diameter shaft does not deflect in operation and carries only minimum torsional load. Thus, wear-free running of the impellers is ensured.

Outer ball bearings

The drive shaft is carried in generously dimensioned anti-friction bearings protected by a radial seal ring. These bearings rarely need unscheduled replacement. with L-10 rating in excess of 3 years. Oil bath bearing housing is an option for pumps with 50 and 65-mm (2 and 3") discharge flange.

Internal slide bearings 

The internal bearings are of the sleeve type, positioned in the pumped liquid. Standard material for shaft sleeves and thrust bearings is pure Silicon Carbide, highly resistant against corrosion and wear. Standard material for the stationary bearings is carbon but Silicon Carbide is also available on request.

Suction impeller

To achieve low NPSH-conditions, a centrifugal impeller with enlarged eye area is located on the suction side.

Diffuser

Since these pumps can handle relatively large amounts of gas, they are inherently self priming as long as sufficient liquid remains in the pump. The diffuser is designed as a retaining stage which enables the pump to self-prime when re-started.

NPSH conditions

When handling boiling liquids or hydrocarbons, the required liquid level on the suction side (NPSHR) can be reduced to 50% of the NPSH-value for water.

Hazardous area features

Unlike Canned-motor designs, magnetic driven pumps do not have electric windings adjacent to the fluid in the shroud and the power transfer by magnet flux is inherently safe.

Magnetic coupling 

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 and no contact with the liquid occurs.

Energy is transmitted to the hermetically sealed liquid end by a bank of external magnets passing motive force through the sealing shroud to a bank of internal magnets. Inner and outer magnet rings are locked together by magnetic forces and work as a synchronous coupling. The inner magnet ring transmits the required torque direct to the impeller. The magnetic drives are designed for electric motors with direct on line starting. Should a subsequent increase of motor power be required, the nominal power of the coupling can be increased by adding further rows of magnets. The maximum transmissible power for SCM couplings is 53 HP at 1750 rpm.

Internal circulation

When the pump is in operation it generates eddy currents which heat up the shroud and the product in the magnet area. This heat is dissipated by internal circulation. The circulation flow is led from the discharge through the magnet area and the pump shaft to the suction disk of the last stage. Pressurizing of the shroud prevents flashing of the liquid in the magnet end.

Temperature control

The major heat source of magnetic driven pumps is in the shroud area, which is cooled during normal running by the pumped liquid. Nearly all malfunctions can be detected by monitoring the liquid temperature in the shroud 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.

Shroud protection

In the event of a ball bearing failure, the generous clearances between outer rotating magnets and the stationary shroud prevent rubbing of the magnets on the shroud surface. In such cases, the cover will contact the bearing housing first due to the smaller clearance between these parts.

Dry running protection

Due to the small clearance between the side channel impellers and the stage disks, this type of pump will not tolerate dry running. For protection, a level control in the suction line is recommended. At self-priming conditions with a suction liquid level below the pump centerline, an Optoelectronic level detector can be fitted in the diffuser to monitor the liquid level in the pump.

Materials

Depending on the requirements, the following materials are provided for SCM-pumps. Special designs on request.

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