NMWR Hot Oil Circulation Pump
Featured Product from Dickow Pump Company, Inc.
NMW/NMWR/PRMW-pumps are single stage volute casing pumps with closed impellers, back-pull-out design, with end suction and top centerline discharge flange. Foot mounted casings are provided as standard. Centerline mounted design is available as an option. Performance data and flange-to-flange dimensions comply with EN 22858 (ISO 2858).
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 the outer drive magnets, passing motive force through the containment shell to the internal drive magnets. Inner and outer magnets are locked together by the magnetic field lines and are working synchronously without any slip.The inner magnet ring transmits the required torque directly to the impeller. Overload of the magnetic coupling and slipping will not effect demagnetization if a reliable monitoring device prevents overheating of the magnets. During operation, the rotating field lines pass through the metallic containment shell and generate magnetic losses. The magnetic couplings are sized for direct- on-line starting of the electric motors. The transmissible power of a coupling depends on the axial magnet length. The couplings are sized for the maximum power consumption of the rated impeller at the end of performance curve. The rated coupling power can be increased by mounting an additional series of magnets, required e.g. when installing a larger impeller and respectively, motor.
The internal clearance between inner magnets and containment shell depends on the wall thickness of the containment shell. However, a minimum clearance of 1 to 2 mm (0.039 - 0.078") is provided in any case. This, together with wear resistant sleeve bearings, allows handling of fluid with solids.
Temperature monitoring, power monitoring, dry running protection devices, leakage detection systems are available. Ask DICKOW engineers for further details.
To avoid cavitation, the impellers of the NMW/NMWR/PRMW-pumps are designed to achieve low NPSH-values. For pumps with discharge above 50 mm (2"), optional inducers are available for further improvement of NPSH-required conditions. The inducers are designed such that NPSH- improvement is given from minimum flow up to BEP. Retrofit of inducers on site is possible by remachining the volute casing, without changing the suction pipe.
Volute casing and magnet end have separate drain connections.
During start-up and filling of the system with open suction valve, the pumped liquid enters the magnet end through holes in the sleeve bearings and the gap between pump shaft and bearing housing. Remaining air in the containment shell will be vented by the two valve venting system according to the manual instructions.
Balanced thrust loads
The thrust loads of the closed impellers are balanced by wear rings, balance holes in the impeller hub, and back vanes. Residual forces on the impeller are acting in the suction flange direction. These forces will be balanced by the rotor design. The difference between the constant pressure at the rear rotor area and the variable pressure at the front side creates a counter force acting in direction to the containment shell. The value of this reaction force depends on the variable gap S. This meansthat the internal rotor floats until the forces at impeller and rotor are balanced. The thrust bearings work as start-up rings only.
Magnetic coupled DICKOW-pumps of the series NMW/PRMW are of sealless design. The containment shell forms a closed system with hermetically sealed liquid end.
The magnetic driven NMW/PRMW-pumps are designed for hot oil applications, to improve plant and personnel safety in industrial heating plants. Mechanical seals are eliminated. No utility cooling needed. In these cases, double mechanical seals are required in conventional pumps.
Why Use Dickow Magnet Drive Pumps?
Since the 1970s concern for the environment has become increasingly important in the design of industrial plants. Today this issue is a vital concern in any discussion involving new plants and updating of facilities. Equipment designers, engineers, and suppliers must offer solutions which will eliminate any adverse environmental impact, or at a minimum reduce it to sustainable or regulated levels.
The weakest link with respect to centrifugal pumps is the shaft seal, when considering release of fluids to the environment. This is because there is always some inherent emissions from mechanical seals. The average emission rate of a mechanical seal is 0.13 GPM to 0.35 GPM, and although this appears to be quite small, the actual atmospheric penetration is quite large when one considers that large chemical plants have thousands of pumps in operation. In 1989 the Environmental Protection Agency (EPA) published its first report on environmental pollution. The report documents that American chemical and petrochemical industries, in 1987, emitted 390 tons of toxic materials into the atmosphere, in part attributable to pump leakage.
Potential problems occur by the formation of dangerous explosive mixtures, which become worse when toxic or malodorous gasses and vapors endanger plant personnel. In order to prevent the vaporization of liquids between seal faces additional cooling is required when the media has vapor pressure greater than atmospheric pressure at operating temperatures. Additionally, when handling fluids that crystallize in the atmosphere, an appropriate quench connection or barrier fluid must be provided.
Various attempts have been made to improve the performance of mechanical seals in order to meet regulations pertaining to emissions. Examples include double acting mechanical seals of "tandem design", "back-to-back design", and various gas seal types. All of these require auxiliary equipment, systems, and controls. For many applications the costs of this equipment is not justifiable in light of the gains attained.
It would appear that the outer limits have been reached for improvements in mechanical seals with regard to reliability and emissions control. The only realistic solution is a sealless pump with zero leakage, i.e. without the connection of the media to the environment due to the absence of a seal. Many of our earliest customers installed Dickow sealless magnet drive pumps for their zero leakage feature, but quickly realized that their mean times between failures was greatly improved as down time due to seal replacement was eliminated completely.
Dickow Pump Company has produced pumps for over 100 years. Our pumps are working steadily and dependably in all corners of the globe.
As the technical world leader in magnetic drive pumps, Dickow holds many patents, is ISO 9001 certified, and is a supplier-partner of major chemical companies.
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