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Magnetically coupled pumps

Magnetically coupled pumps or pumps with magnetic drive, vary the style of traditional pumping, that the motor is coupled to the pump by magnetic means rather than by a direct mechanical shaft. The pump operates through a drive magnet, “conduct” of the pump rotor, which is magnetically coupled to the drive shaft driven  they are often used where a leak of the pumped fluid poses a great risk (for example, fluid aggressive. electric shock of chemical or nuclear, industry or – garden fountains). They have no direct link between the engine and the propeller shaft, so the gland is necessary. There is no risk of absconding, unless the enclosure is broken. Since the pump shaft is not supported by external bearings of the pump casing, press inside the pump is ensured by rings. The size of the pump of a magnetic drive pumps can range from a few watts of power from 1 MW to a giant. The construction consists of a metallic material and non-metal executions. MagDrive metal pumps are generally less effective than traditional pumps mechanical seals. The reason is a loss of power in the magnetic trasmission. This loss is called Eddy current and a magnetic drive pump can reach 20% and more of the installed power. This is due to the presence of the metal containment system in the magnetic field of emission. Latest innovation in technology of the pump drive magnetic effectiveness downplayed the absence, between pumps with magnetic drive and seals mechanical pumps. In some cases today there is more difference between this class of two pumps. In fact, the introduction of non-metallic containment shells reduced or eliminated the eddy currents generated in the coupling.

Below a summary of actually present materials on the market of the containment shell.

The comparison is based on a magnetic drive 18.5 kW installed centrifugal pump, turning at 2900 RPM.

Material / Technology Approx. Thickness [mm] Pressure Rating [bar] Temp. Field [°C] Magnetic Losses [kW] Comment
Hastelloy / other metallic alloys 1.2 – 1.7 PN 16 to PN 50 -90°C / +350°C 2.6 Most common, less efficient
Hybrid Containment shell 1.6 PN 50 -0.36 0.78 innovative
PEEK composite 3.5 – 5.5 3.5 – 5.5 -40°C / +120°C 0 High thickness, cost and temp. limits
Zirconium oxide 4-7 PN 16 -190°C / +350°C 0 High thickness, High cost
Borosilicate glass 3-7 PN 10 -40°C / +180°C 0 Weathering, high thickness, Pressure/Temp. limits

The only solution available on the market that can minimize Eddy current losses and keep metal hull in contact with pumped liquid is hybrid containment. This has a minimum of magnetic losses, but at high temperature and pressure resistance, for this reason most adapt at the request of heavy weight.

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Problems of centrifugal pumps

These are a few difficulties in centrifugal pumps:

- Cavitation – the suction head positive net (NPSH) of the system is too low for the chosen pump

- The wheel wear – can be exacerbated by suspended solids

- Corrosion inside the pump caused by the properties of fluids

- Overheating Due to low flow

- Leakage along rotating shaft lack of boot centrifugal pumps must be completed (with the pumped fluid

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- Surge

A fields solids control system oil require lots of centrifugal pumps to sit on or in slurry tanks. Types of centrifugal pumps used are sand, submersible slurry pumps, shear, and the pumps of load. They are defined by their different functions, but their principle of operation is the same.

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Vertical centrifugal pumps and Multistage centrifugal pumps

Centrifugal vertical pumps are also called cantilever pumps. They use a unique tree and configuring bearing support which allows the casing to hang in the pit while the bearings are outside the sump. This style of pump use gland to seal the shaft but uses a “bottleneck socket”. A common application for this style of pump is in a parts washer.

A centrifugal pump containing two or more wheels is called a multistage centrifugal pump. The wheels can be mounted on the same shaft or on different trees. For pressures higher output, the wheels can be connected in series. For the output of higher throughput, the wheels can be connected in parallel.

A common application of the multistage centrifugal pump is the boiler feed water pump. For example, a 350 MW unit, should be two feedpumps in parallel. Each supply is a multicellular pump produce 150 l / s at 21 MPa. All of the energy transferred to the fluid is derived from the mechanical energy of the rotor drive. This can be measured to isentropic compression, resulting in a slight increase in temperature (in addition to the increase in pressure).

In the mining industry, or in the extraction of oil sands, the foam is generated to separate bitumen from sand and clays and minerals. Foam contains air that tends to block the conventional pumps and cause a loss of prime. Historically, the industry has developed ways to cope with this problem. In the industry of pulp and paper holes are drilled in the wheel. Air escapes on the back of the wheel and a special expeller evacuates the air to the suction tank. The wheel can also featured small special fins between the primary blades called blades cracked or secondary blades. Some pumps may have a large eye, inducer or recirculation of foam under pressure of the pump back to the aspiration to break bubbles.

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How centrifugal pumps works

Fraction angular velocity of rotation of the movement and the angular velocity of rotation of the wheel appeal Rotary transfer fω factor = 1 for the impeller blades right fω < 1, it variable from 0 to 1 depend on the discharge of the pump impeller blades curved backwards.

General explanation: as most of the pumps, centrifugal pump converts the rotational energy, often from an engine , the energy in a moving fluid. Part of the kinetic energy into continuous energy of the fluid. The fluid enters the eye through the axial of the envelope, is caught in the propeller and is swirled tangentially and radially outwards until it left through all hoop of the impeller in the part of diffuser of the housing. The fluid gains to both the speed and the pressure through the wheel. The diffuser fritter, or scrolling, the section of the envelope-shaped slowed the flow and increases the pressure.

Compare the two the old way and the new description how the energy of power of the turbine for the object passes through it, we see: new way shows how centrifugal force appears and it is effective on an object through the wheel. While that the old way that mentioned about the interaction of the force of inertia between the van of the turbine and the object, which means that the main conservation of momentum can never describe the centrifugal force whose energy relationship with her, because she is diametrically force it cannot make the couple on the rotating shaft.

Application of the theory of classical mechanics, assuming that the viscosity of the liquid equal to 0 and no loss of energy for the work of energy transfer from the wheel to power lines which means that all the distinct flows will be uniform (this approximation of physical reality to get the simpler than the State solid mechanism of hydraulic mechanism)

Observe a mass going along a straight wheel (the wheel the more old and simple), it is these forces impact on him:

1 – thrust wheel on it a CF force, it reflects a force anti F ‘ on pallet

2 – centrifugal force Fc pull fly (follow the centrifugal direction)

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History of centrifugal pumps

Centrifugal pumps are a subclass of the turbomachinery by dynamic absorbing work revolution. the centrifugal pumps are used to transport fluids through the conversion of the kinetic energy of rotation to the hydrodynamic energy of the fluid flow. The rotational energy usually comes of an engine or an electric motor. The fluid enters the wheel pump along or near the axis of rotation and is accelerated by the impeller, flowing radially outward in a room diffuser or volute (casing), Jāzeps it.

Common uses include air, water, sewage, oil and petrochemical pumping. The inverse function of the centrifugal pump is a turbine water by converting the potential energy of water into mechanical energy of rotation pressure.

According to Reti, the first machine that could be characterized as a centrifugal pump is a machine of the lifting mud that appeared as early as 1475 in a treatise by the Italian Renaissance engineer Francesco di Giorgio Martini. pumps centrifugal real were not developed until the end of the 17th century, when Denis Papin built one using straight blades. Curved Dawn was introduced by the British inventor John Appold in 1851.

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