What is the difference between shielded pumps and magnetic drive pumps?

This post was last edited by 654262293 on 2010-12-20 14:17. A magnetic pump is a type of special pump. It is a leak-free fluid transfer mechanism that does not rely on dynamic seals; it is designed primarily for centrifugal pumps used in vane pumps, and typically consists of a pump body, a separation sleeve, and connecting components to form a pressure-resistant shielded sealing chamber. Outside the sealed chamber, there is a rotating permanent magnet field; through the effect of this magnetic field, the magnetic rotor components inside the sealed chamber are driven to rotate synchronously in a contactless manner. The rotor components inside the sealed chamber then drive the impeller to perform work on the fluid. Since the shielded sealing chamber composed of stator components lacks dynamic seals, and the rotating shaft that drives the impeller to perform work does not extend out of this shielded sealing chamber, this ensures zero leakage and no contamination in the magnetic pump. 1. Principle and structural features of shielded pumps: In ordinary centrifugal pumps, the drive mechanism involves connecting the impeller shaft of the pump to the motor shaft through a coupling, thereby causing the impeller to rotate together with the motor. A shielded pump, on the other hand, is a seal-less pump; both the pump and the drive motor are enclosed within a pressure vessel filled with the medium to be pumped. This pressure vessel has only static seals, and an electrical winding set is used to generate a rotating magnetic field that drives the rotor. This design eliminates the rotating shaft sealing mechanism found in conventional centrifugal pumps, thereby achieving complete leaklessness. A shielded pump combines the pump and the motor together; the rotor of the motor and the impeller of the pump are mounted on the same shaft. A shielding sleeve is used to separate the rotor from the stator of the motor. The rotor rotates within the medium being transported, with power being transmitted to it through the magnetic field of the stator. Furthermore, the manufacturing of shielded pumps is not complex; their hydraulic section can be designed and manufactured according to the structural types commonly used in centrifugal pumps as well as relevant standard specifications. 2. Advantages and disadvantages of canned pumps 2.1 Advantages of canned pumps (1) Fully enclosed. There are no dynamic seals in the structure; only static seals are present at the pump’s casing, which enables complete leak-free operation. It is particularly suitable for transporting flammable, explosive, valuable liquids, as well as toxic, corrosive, and radioactive liquids. (2) High safety. Both the rotor and the stator are equipped with shielding sleeves to prevent them from coming into contact with the material; even if these shielding sleeves are damaged, there is no risk of external leakage. (3) Compact structure with low land occupation. The pump and motor are integrated; no centering is required for disassembly or assembly. It has low requirements for the base and foundation, requires little routine maintenance, and results in low maintenance costs. (4) It operates smoothly, produces low noise, and requires no lubricating oil. Due to the absence of rolling bearings and motor fans, no lubricant is required, and it produces low noise. (5) Wide range of applications. It can meet the requirements for various operating conditions such as high temperature, high pressure, low temperature, and high melting point. (6) Compared to pumps with seals, it eliminates the hassle of maintaining and replacing seals, as well as the need for couplings; it has a smaller number of components (about 30% of those in mechanically sealed pumps), resulting in higher reliability. Fans without rolling bearings and motors do not require lubricant, and they operate smoothly with low noise. A configurable bearing wear monitor can be used to detect the wear of bearings. (7) It has a compact structure, occupies little space, has low requirements for the base and foundation, eliminates the alignment issues associated with couplings, and is easy to install at low cost. There is less daily maintenance work, resulting in lower maintenance costs. (8) It can operate properly without leakage in a vacuum system or under conditions of alternating operation between \"vacuum\" and \"positive pressure\". It is possible to transfer materials directly from the vacuum tank to other containers under high vacuum conditions. It has a wide range of applications and can meet the requirements in various operating conditions such as high temperature, high pressure, extremely low temperatures, and high melting points. 2.2 Disadvantages of shielded pumps (1) Since shielded pumps use sliding bearings and are lubricated by the medium being transported, media with poor lubricity are not suitable for transportation using shielded pumps. Generally, the viscosity suitable for shielded pump media is 0.1 to 20 mPa·s. (2) The efficiency of shielded pumps is usually lower than that of centrifugal pumps with single-end mechanical seals, but it is roughly comparable to that of centrifugal pumps with double-end mechanical seals. (3) Operating for long periods at low flow rates results in lower efficiency of the shielded pump, which leads to heating and liquid evaporation, causing the pump to run dry and thus damaging the sliding bearings. (4) Since sliding bearings are used and the conveyed medium is utilized for lubrication, shielded pumps are not suitable for transporting media with poor lubricity. The medium viscosity range generally suitable for shielded pumps is 0.1–20 cP. (5) The efficiency of shielded pumps is usually lower than that of sealed centrifugal pumps. However, at medium and low power levels, the overall efficiency difference is not significant compared to double-end face seal pumps, as the latter have increased power consumption due to their cooling and flushing systems. (6) When the centrifugal pump is in operation, the flow rate must be higher than the minimum continuous flow rate. This is particularly important for shielded pumps, as at low flow rates the pump’s efficiency is low, which leads to heating; this in turn causes the fluid to evaporate, resulting in the pump running dry and damaging the sliding bearings. 3. Types and application ranges of canned pumps Based on factors such as the temperature, pressure, viscosity of the liquid being transported, and the presence of particles, canned pumps can be classified into the following types: (1) Basic type: The temperature of the medium being transported does not exceed 120°C, and the head is not more than 150 m. All other types of shielded pumps can be obtained by modifying and improving the basic model. (2) Reverse circulation type: In this type of shielded pump, the flow direction of the liquid used for bearing lubrication, cooling, and motor cooling is exactly the opposite of that in the basic type. Its main feature is that it is less prone to cavitation, making it particularly suitable for transporting liquids that are easy to vaporize, such as liquefied petroleum gas and chloromethane. (3) High-temperature type: The maximum temperature of the medium being transported is generally 350°C, the maximum flow rate is 300 m3/h, and the maximum head is 115 m. It is suitable for high-temperature liquids such as hot oil and hot water. (4) High-melting-point type: The pump and motor are equipped with jackets, which significantly improves the heat resistance of the motor. Suitable for high-melting-point liquids, with a maximum temperature of up to 250°C. Steam or a liquid at a certain temperature can be introduced into the jacket to prevent crystallization of liquids with high melting points. (5) High-pressure type: The casing of a high-pressure type shielded pump is a high-pressure vessel, enabling the pump to withstand very high system pressures. To support the shield casing under internal high pressure, the stator coils can be used to bear the pressure. (6) Self-priming type: When the suction pipe is not filled with liquid, the pump expels liquid through automatic vacuum creation, making it suitable for extracting liquid from underground containers. (7) Multi-stage type: Equipped with multiple impellers, suitable for high-head fluid transfer, with a maximum head of up to 400 m. (8) Slurry type: Suitable for transporting liquids mixed with a large amount of slurry. 4. Precautions for selecting shielded pumps: Generally, shielded pumps use some of the liquid being transported to cool the motor, and since the gap between the components is very small, the liquid to be transported must be clean. When transporting mixtures of various liquids that may produce precipitates, coking, or gels, the use of a shielded pump (non-slurry type) in such cases can lead to blockage of the shielding gap, affecting the pump’s cooling and lubrication and ultimately causing damage to the graphite bearings and motor. Shielded pumps generally come equipped with circulation cooling tubes; when the ambient temperature is below the freezing point of the liquid being pumped, anti-freezing measures such as insulation sleeves should be employed to ensure easy pump startup. Additionally, when starting a shielded pump, it is essential to strictly follow the correct sequence for opening the outlet valve and the inlet valve. When shutting down the pump, first reduce the opening of the outlet valve; once the pump has stopped running, close the inlet valve first and then the outlet valve. In short, the use of shielded pumps ensures complete leaklessness, effectively preventing environmental pollution and material loss. As long as the right model is selected and the operating conditions remain stable, there is almost no need for maintenance during normal operation. Shielded pumps are ideal for transporting flammable, explosive, corrosive, and valuable liquids.

Projects: Ordinary centrifugal pumps, shielded pumps (a type of centrifugal pump). Consequences of damage to the isolation sleeve (or shield): The medium leaks into the atmosphere. There is a second leak prevention layer (the motor casing) that can prevent the medium from leaking out, but this can easily damage the motor stator. Efficiency: 10.9. Requirements for manufacturing technology and equipment: Lower requirements / Higher requirements. Drive unit standard: Dedicated motors for use with these pumps. Noise level: Slightly higher / Slightly lower (the motor does not have a fan). Axial length: Longer / Shorter. Coupling: Present / Absent. Bearing wear detector: Present. Price: Higher than that of ordinary centrifugal pumps. Ease of routine maintenance and repair: Difficult; the motor can be damaged due to idling. Transport capacity: Lower than that of ordinary centrifugal pumps. Application range: Power (kW)/Temperature (°C): Similar/similar. Suitable for media at normal temperature and pressure that are clean and do not easily vaporize: Good/good. Suitable for media that are easy to vaporize at normal temperature and pressure: Moderate; not suitable in all cases. There are dedicated models available. Media containing solid particles: Generally not suitable; there are models designed for use with media containing solid particles (external cleaning fluid is required). Media with high melting points and tendency to crystallize: Generally not suitable; there are dedicated models available. Highly corrosive media: Good; not suitable (due to limitations related to the thickness of the shield). Flammable, explosive, or toxic media: Generally, better leak prevention performance