General

Magnetic driven DICKOW - pumps of the series NM are sealless pumps. The static containment shell forms a closed system with hermetically sealed liquid end.

Applications

Magnetic driven NM-pumps are design 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.

Maximum capacity appr. 320 m³/h (1408 US-gpm), differential head 146 mLC (480 ft). Max. temperature for NMW-type 400°C (752°F) without external cooling. The maximum allowable working pressure is 40 bar (580 psi).

Construction

NML-pumps are single stage volute casing pumps with closed impellers, back-pull-out design, with end suction and top discharge flange. Sturdy legs are provided as standard for foot mounting on the base plate. Centerline mounted design is available on request. Capacity and outer dimensions comply with EN 22858 (ISO 2858).

If DICKOW-pumps of series NCL with mechanical seals are already in operation, a modification to magnetic drive is possible without removing the volute casing from the piping.

Design Features

Containment shell

The containment shell is designed as a pressurized vessel to separate the pumpage from the atmosphere. The containment shell is not used as an additional bearing holder. No dynamic stresses occur. The containment shell is bolted to the bearing housing in a manner that allows removal of the bearing bracket including outer magnets and ball bearings without exposing the pumpage 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.

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 forces and work 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 affect demagnetization. The magnetic drivers 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 appr. 165 kW at 2900 rpm (265 HP at 3500 rpm).

Internal clearances

The internal clearance between inner magnets and containment shell depends on the thickness of the containment shell. For 1 mm (0.039") thickness, a clearance of 1,8 mm (0.071") will be provided. This allows - together with wear resistant sleeve bearings - handling of solid containing fluids.

Containment shell protection

The clearances between the bearing bracket and the outer magnet coupling and between the outer magnet coupling and the containment shell are arranged to prevent the outer magnet coupling rubbing on the containment shell even in case of ball bearing failure.

Internal circulation

Pumps in operation generate eddy currents in the metallic containment shell which heat up the product in the gap between rotor and containment shell. This heat is dissipated through an internal circulation. The internal circulation flows from discharge, directly behind the impeller, through the pump shaft to the rear impeller. The pressure increase trough the rear impeller allows a circulation back to the discharge side.

This pressurization of the magnet end and the sleeve bearing prevents also vaporization of the pumpage in this area.

Casing drain

Complete drainage of casing and magnet end is possible through casing drain. No additional drain in the containment shell area is required.(Except for type NMW)

Outer ball bearings

The drive shaft is supported by generously dimensioned antifriction bearings, grease filled for life time and protected against environment by a radial seal ring. An oil mist or oil bath API-bearing housing can be provided as an option.

(refer to type NMR)

Double sleeve bearings

The double internal bearings are positioned in the pumped liquid. The stationary bearings are located centrally in the bearing housing, which grants proper alignment for true running. Standard material is pure Silicon Carbide with diamond layer providing limited dry-run capability. SIC is highly resistant to corrosion and wear.

The Silicon Carbid parts are shrink fitted and therefore, protected against shock and thermal stress.

NPSH-Conditions

Due to internal circulation from discharge to discharge, there is no temperature elevation in the impeller eye. Handling of boiling liquids is therefore possible and an increase of NPSH-required is not given.

Balanced thrust loads

The thrust loads of the closed impellers are hydraulically balanced by wear rings, injection holes and by impeller back vanes.

During operation the pressure P4 in the rear rotor area is lower than the pressur P5 on the front. This pressure difference, depending on the variable gap S, generates counter forces which balance the floating internal rotor until all forces are reduced to zero.

Temperature control

Connections for temperature monitoring of the internal circulation flow and the containment shell surface are available as standard.

Monitoring devices for outer ball bearing available on request.

For critical applications, the MAG-SAFE protection system is recommended.