The structure and principle of the shield pump are the same as that of the ordinary centrifugal pump. The difference lies in the driving motor. The motor of the shield pump is completely enclosed in the second layer of isolation sleeve or shield sleeve, and the leakage prevention mainly depends on the internal anti-corrosion shield sleeve.
Definition of canned motor pump: it is driven by canned motor with stator winding and rotor winding respectively placed in sealed metal cylinder, and the pump casing and the drive motor casing are sealed with flange, thus eliminating the pump with shaft dynamic sealing structure. Suitable for transporting precious liquid or liquid with radioactivity. Applied discipline: electric power (first level discipline); nuclear power (second level discipline)
The driving of ordinary centrifugal pump is to connect the impeller shaft with the electric shaft through the coupling, so that the impeller and the motor can rotate together and work, while the shield pump is a kind of unsealed pump. Both the pump and the driving motor are sealed in a pressure vessel filled with pumped medium. This pressure vessel only has static seal, and a wire group provides the rotating magnetic field and drives the rotor. This structure cancels the rotary shaft sealing device of the traditional centrifugal pump, so it can be completely leak free.
The shield pump connects the pump and the motor. The rotor of the motor and the impeller of the pump are fixed on the same shaft. The shield sleeve is used to separate the rotor and the stator of the motor. The rotor operates in the medium being transported, and its power is transmitted to the rotor through the stator magnetic field.
In addition, the manufacture of canned motor pump is not complicated, and its hydraulic end can be designed and manufactured according to the commonly used structure and relevant standards and specifications of centrifugal pump.
Shielding pump structural style：
1. The motor and the water pump have an integrated structure, and the water pump and the motor are coaxial connected;
2. The inner side of the motor stator and the outer side of the rotor are provided with a shielding sleeve, and the inner side of the shielding sleeve is communicated with the pump;
3. There are two installation methods: horizontal and vertical
4. The cooling fan is removed from the motor, and the motor is cooled by circulating medium between the stator and the rotor. At the same time, the surface of the motor base is used for cooling.
Shielding pump product characteristics:
1. The integrated structure of motor and pump adopts static seal to make the electric pump completely leak free;
2. Fully closed and leak free structure can transport toxic and harmful liquid substances;
3. The shield type water-cooled motor and cooling fan are used to make the pump operate in low noise and mute mode, which is suitable for the occasion with high requirement of environmental noise;
4. In recent years, the material of the bearing has SiC, super hard and so on, and its service life is better than that of the graphite bearing.
5. The vertical structure can be installed on the pipeline like a valve, which is convenient and quick to install. During maintenance, only the motor and impeller can be pulled out without removing the pipeline.
6. It can be installed and operated with shock absorber or shock pad to reduce the noise of electric pump during operation.
Shielding pump concrete form：
1. Basic type of conveying common materials;
2. The reverse circulation type and the reverse pressure type for conveying the materials easy to vaporize;
3. High temperature separation type for conveying high temperature materials, usually the temperature is below 350 ℃;
4. Mud type for conveying granular materials;
5. High melting point type for conveying high melting point materials;
6. The liquid level of the conveying material is lower than the self-priming type at the suction port of the pump, and the self-priming height shall be lower than 5m.
Shielding pump application:
1. Ground source heat pump air conditioning circulating water system;
2. LiBr air conditioning unit air conditioning pump, transformer oil pump, locomotive pump, etc;
3. Heating and circulating water system;
4. Fire water pressurization system;
5. Tap water pressurization system.
II. Industry and military aerospace
1. Transportation of toxic and harmful liquid for chemical and pharmaceutical industries;
2. Fueling before launch of space rocket;
3. Nuclear grade shielded electric pump for nuclear power plant.
Shielding pump components:
The main components of canned motor pump are impeller and volute of centrifugal pump. However, because the main body and driver of the pump are enclosed in a pressure vessel filled with pumped medium, the pressure vessel has static seal, but there is no traditional dynamic seal of rotary pump. And static seal is easier to achieve complete seal than dynamic seal. Therefore, canned motor pump can achieve complete leak free
Shield pump is mainly used to transport flammable, explosive, highly toxic and other petrochemical liquids in order to improve the safety and reliability of petrochemical plant operation
The shield pump uses the same shaft to fix the rotor of the motor and the impeller of the pump together, and then uses the shield sleeve to shield this group of rotors. The stator of the motor surrounds the shield sleeve. The shield sleeve is made of metal, so the power can be transmitted to the rotor through the magnetic field. The whole rotor is running in the pumped liquid. The end of the shield depends on the flange or welded structure The shield is actually a pressure vessel
In addition to the shielding sleeve, there is also a circulating pipe. The use of pumped liquid plays a very important role in bearing lubrication and cooling, and sometimes motor cooling
The inner surface of the stator and the outer surface of the rotor are equipped with the stator shield sleeve and the rotor shield sleeve made of corrosion-resistant metal sheet. Each end face is welded with them with corrosion-resistant metal sheet. They are separated from the transported liquid, so that the stator winding core and the rotor core are not corroded
Generally, a small part of delivered liquid (about 1% – 3% of total flow) is introduced into the circulation pipe from the pump discharge. After filtering, it passes through the circulation pipe, first lubricating and cooling, then bearing, then cooling through the clearance between the stator shield and the rotor shield, then lubricating and cooling the front bearing, and finally returning to the impeller inlet hole through the impeller balance hole
The shield sleeve of the shield pump, that is, the stator shield sleeve and the rotor shield sleeve, is used to prevent the transmission medium from being immersed in the stator winding and the rotor core. However, due to the existence of the shield sleeve, the gap between the motor stator and the rotor increases, resulting in eddy current in the shield sleeve, resulting in the decrease of the motor performance and the increase of the power loss
In order to reduce the power loss, the inner diameter of the stator of the shield motor is usually small, the wall thickness of the shield sleeve is as thin as possible, and the shield sleeve material is non-magnetic material. Therefore, the shield motor is usually a slender structure. Most of the shield sleeve materials are 304, 304L and 316316L stainless steel. Although the eddy current loss of Hastelloy C and titanium materials is small, but the cost is high, so they are rarely used. The thickness of the shield sleeve is generally 0.2-1mm.
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