Regarding the principle of shielded pumps

A canned pump is a type of centrifugal pump; what sets it apart from ordinary centrifugal pumps is that its motor and impeller are located within the same casing. The fluid inside the casing serves both as the working medium and as a lubricant. Therefore, it is necessary to remove air from the casing before starting the pump – otherwise, the pump will be damaged. Its advantage lies in the fact that there are no moving parts outside the casing, which eliminates the risk of leakage from mechanical seals; hence it can be used for transporting toxic or valuable substances.

Please see the performance features and selection criteria for shielded pumps at http://bbs.hcbbs.com/viewthread.php?tid=67728

http://bbs.hcbbs.com/viewthread.php?tid=101080 Working principle and characteristics of shielded pumps

The shielding pump referred to in general terms is the centrifugal shielding pump. Its working principle is the same as that of a centrifugal pump: the rotation of the impeller generates centrifugal force, which causes the liquid inside the impeller to be forced away from it, converting kinetic energy into pressure energy, thereby enabling the transport of the medium. The key to the operation of a shielded pump lies in making use of the interaction between the motor stator and rotor; the rotor and impeller are connected by a single shaft, and a very thin shielding sleeve is used to separate the coils of the stator and rotor from the fluid being transported, thereby converting dynamic sealing into static sealing. Due to the pressure difference, the medium flowing between the stator and rotor forms a circulation, which cools the motor and bearings and lubricates them; therefore, a shielded pump does not require external lubrication.

Shielded pumps are primarily used for transporting toxic, flammable and explosive, highly corrosive, radioactive, and valuable liquids; therefore, a large number of such pumps are employed in the organic chemical industry. Cage pumps are expensive, and their maintenance is an important task.

The main structural feature of a shielded pump is the absence of a shaft seal; the sealing of the pump is achieved by integrating the pump and the motor into a single unit. The specific features are as follows: 1. No leakage of the liquid being processed at all. Suitable for handling highly corrosive liquids, liquids with high volatility and a risk of explosion or fire, as well as toxic and harmful liquids. 2. It does not draw in air or other substances from the outside. It has good airtightness and can be used in vacuum systems. 3. No lubricant or sealant is required. Since shielded pumps do not require lubricating oil (grease) or sealing fluid for the shaft seal, the liquid being processed is not contaminated, making them suitable for processes that demand high purity. 4. Simple structure with few components. Compared to conventional process pumps, shielded pumps lack components such as couplings and shaft seals, thus **reducing the number of parts**. 5. Compact structure with small footprint. Since the pump and motor of a canned pump are integrated, its structure is very compact, requiring little installation space. Additionally, small canned pumps can be installed directly on pipes without the need for a foundation. 6. Easy to maintain. The maintenance of shielded pumps mainly involves replacing the bearings and shaft sleeves; since there is no coupling, alignment is not required during disassembly and assembly, making it easy to take them apart for inspection. 7. Low noise level. It has a cooling system, eliminating the need for a motor cooling fan, thus resulting in low noise

1. The presence of the shielding sleeve increases the gap between the stator and the rotor, reducing the motor’s efficiency. 2. When selecting the material for the shielding sleeve, in addition to considering corrosion resistance, its non-magnetism and high resistivity must also be taken into account, in order to reduce the additional power losses incurred by the motor due to the presence of the shielding sleeve. 3. As the medium flows within the motor, the rotation of the rotor will encounter frictional resistance from the medium

1. Based on the arrangement of the pump and motor, there are two types: vertical shielded pumps and horizontal shielded pumps. 2. Classified by the flow pattern of the circulating coolant, the circulating liquid in a shielded pump serves three purposes: one is to cool the motor and bearings ； Second, it lubricates the bearings and carries away wear products. Classified by the flow pattern of the circulating coolant: internal circulation canned pumps, external circulation canned pumps, and mixed circulation canned pumps. 3. Classified by the dry/wet condition of the motor stator: 1) Dry-stator type shielded pump. The stator of the motor is protected by a shield made of specialized non-magnetic material, and the stator protection chamber is filled with air or an inert gas to prevent the stator coils from being affected by the working fluid. 2) Wet-stator type shielded pump. There are two types of this format: (1) It is similar to the dry stator structure, with only oil such as transformer oil filled in the stator cavity. This type, together with the dry-stator type, is collectively referred to as the shielded motor type. (2) There is no stator shield, and the coolant is introduced directly into the stator cavity.

A shielded pump works in this way: when the pump is started, the stator generates a magnetic field; the magnetic field lines pass through the shielding sleeve, driving the rotor to rotate. An impeller is attached to one end of the rotor, and as the rotor rotates, the impeller also rotates, thereby pumping the liquid out.

A shielded pump is a special type of centrifugal pump, and its working principle is the same as that of ordinary centrifugal pumps. Structurally, a shielded pump consists of a shielded motor and a pump casing; the stator and rotor are separated from the material by non-magnetic, corrosion-resistant thin-walled sleeves. The rotor is supported by bearings at the front and back and is immersed in the conveying medium; therefore, no type of dynamic seal is required to prevent leakage of the material, and leak-free operation of the pump is ensured entirely by static seals. Even under negative pressure inside the pump, external air cannot enter it.