Special Reports
Shini Self-developed Magnetic Drive Pump
At present, mechanical shaft seal is frequently used for chemical pumps. In spite of improvements on structure and material, leakage of mechanical shaft seal still exists. Because of short service life of bearings, operating life of the common centrifugal pump is also reduced which makes it difficult to prevent leakage. However, the new magnetic drive pump greatly reduces or even eliminates this problem.
Structure of Magnetic Drive Pump
The magnetic drive pump consists of pump head, magnetic driving device and other components. Pump head is composed of impeller, pump body, silicon carbide bearings, shaft sleeve, pump cover and ceramic rod and so on; magnetic driving device is composed of internal and external magnetic connectors, magnetic cover etc; other componentsare bracket, pedestal, motor, central bearing body and coupling and so on.
Magnetic drive pump converts dynamic seal into static seal which achieves hermetic transmission. Compared with mechanical pumps, magnetic drive pump with this structure has peerless advantage that no leakage occurs in any states.
Working Principle
Working principle of magnetic drive pump is: the external magnetic connector rotates as the motor drives it, and the internal magnetic connector rotates synchronously because of the action of magnetic field. Coaxial impeller and internal magnetic connector spins altogether to convey liquid.
As a critical device of magnetic drive pump, the magnetic actuator consists of external and internal magnetic connector as well as magnetic cover. When the motor drives and rotates the external magnetic connector, the internal magnetic connector that connects with the impeller will spin synchronously due to magnetic field. Power is transmitted without contact, so dynamic seal is converted into static seal. The conventional problem of leakage will not happen because the ceramic rod and the internal magnetic connector are fully closed by pump body and the magnetic cover.
Advantages
Magnetic pump introduces magnetic transmission by which the torque is transferred without contact. Static seal thoroughly avoids the long-standing leakage problem occurs during liquid conveying in industry. With compact structure, easy operation, convenient maintenance and stable operation, it reduces labor intensity of maintenance and also the costs.
A closed cavity is formed between the internal magnetic connector and the magnetic cover which lies between the internal and external magnetic connectors. Partial liquid flows into the closed cavity because of pressure difference. It refrigerates the internal and external magnetic connectors and then flows into the impeller inlet without shaft seal problem occurring to common pumps. Magnetic pump prevents liquid leakage and is suitable for conveying corrosive and hot liquid in chemical industry.
Compared with turbine pump utilizing mechanical seal or packing seal, magnetic pump possesses the following advantages:
• Ceramic rod utilizes static seal instead of dynamic seal, medium leakage is prevented.
• Separated lubricant and chilled water is not essential and power consumption is reduced.
• Coupling transmission is replaced by synchronous drag without contact and friction. With low power consumption, high efficiency and especially damping system, the pump is less affected by motor vibration and cavitation shock.
• The internal and external magnetic connectors slip relatively under overload which gives protection to motor and pump.
Important Notices
• Keep off pellets
Iron impurities and granules are not permitted to enter the internal magnetic device in case they rub against bearings.
Flush the pump after conveying medium that easy to crystallize or precipitate (pour water in the pump and discharge it after running for 1 minute) to guarantee the service life of sliding bearings.
Filter the medium containing solid pellets at the inlet of the flow pipe.
• To avert demagnetization
Operate the pump according to the required temperature (below 300℃).
• To prevent dry friction
Idle running is forbidden.
Medium evacuation should be avoided.
The running time of pump should be less than 2 minutes when outlet valve is closed for fear that magnetic failure because of overheat.
Applications
At present in Shini, magnetic drive pumps are mainly used for STM-HT(300℃), they can also be utilized for applications with similar requirements.
Economic Analysis
Price difference between magnetic drive pump and mechanically sealed pump is A=2,400 RMB
Costs of mechanical seal is @B=350 RMB
Labor cost of replacing mechanical seal is @C=100 RMB
Replacement frequency of mechanical seal every year is D=1
Losses of suspending production caused by mechanical seal replacement is @E=3,000 RMB
Break-even point Y (year)
Since A=[(@B+@C+@E) ×D]×Y
Then Y=A÷[(@B+@C+@E) ×D]=2,400÷[(350+100+3,000) ×1]=0.69
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- About Shini USA
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If you want to read other articles, back to2010 Quarter 3 Issue 4.