Is a shielded pump a type of pump, or a type of shaft seal?

A shielded pump is a centrifugal pump without a shaft seal, which ensures no leakage. 1 Principles and structural features of shielded pumps: Ordinary centrifugal pumps are driven by connecting the impeller shaft of the pump to the electric motor shaft through a coupling, allowing the impeller to rotate together with the motor. In contrast, shielded pumps are seal-less pumps; 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 traditional 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 sections can be designed and manufactured according to the structural formats 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 that 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 floor area. 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 lubricant. 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. 2.2 Disadvantages of canned pumps (1) Since canned pumps use sliding bearings and are lubricated by the medium being transported, media with poor lubricity are not suitable for transportation using canned 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 vaporization of the liquid, causing the pump to run dry and thus damaging the sliding bearings. 3 Types and application ranges of canned pumps Depending 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 does not exceed 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 heat transfer oils 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 fluid 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 transport, with a maximum head of up to 400 m. (8) Slurry type: Suitable for transporting liquids mixed with a large amount of slurry. 4 Points to consider when selecting a canned pump: Ordinary canned pumps use some of the liquid being transported to cool the motor, and the gap between the components is very small; therefore, the liquid to be transported must be clean. When transporting mixtures of various liquids that produce precipitates, coking, or gels, using a shielded pump (non-slurry type) in such cases may cause blockage of the shielding gap, affecting the pump’s cooling and lubrication and leading to the damage of the graphite bearings and motor. Shielded pumps generally come equipped with circulation cooling pipes; 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 necessary to strictly follow the sequence for opening the outlet valve and the inlet valve; when shutting down the pump, first reduce the opening of the outlet valve, and after the pump has stopped running, close the inlet valve first before closing the outlet valve. In summary, 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.

A shielded pump is a type of pump that primarily solves the problem of shaft seal leakage; it operates with low noise. Another type of pump is the magnetic drive pump, which is similar to the shielded pump, and each has its own advantages and disadvantages

Shielded pumps have low efficiency, at 60% that of centrifugal pumps; they can only be used for liquids at moderate temperatures that are mostly clean and not volatile. It has high viscosity, causing significant wear to bearings.

It is a type of pump, such as a magnetic pump, used for transporting acids and alkalis. Although its efficiency is low, it represents a good solution for transporting highly corrosive substances.

The maximum idle running time allowed for a canned motor pump is 5 seconds; it will stop operating after 5 minutes of any abnormal condition. The main reason for shutdown is damage to the shielding cover. Canned motor pumps are quite delicate, so during inspections it is important to pay close attention to the TRG pointer of the bearing detector – if it is not in the green area, the pump must be stopped immediately!

The working principle of both shielded pumps and unshielded pumps is the same. They generally belong to the category of centrifugal pumps. Their working principle involves: an impeller rotating at high speed, which imparts energy on the liquid due to inertial centrifugal force, thereby increasing its pressure. Before the water pump starts operating, the pump body and the inlet pipe must be filled with water to prevent cavitation. When the impeller rotates rapidly, the blades cause the water to spin quickly; the spinning water is forced out of the impeller due to centrifugal force. Once the water inside the pump is expelled, a vacuum area forms in the center of the impeller. The water from Suwon is pushed into the inlet pipe through the pipeline network under the action of atmospheric pressure (or water pressure). By repeating this cycle, continuous water pumping can be achieved. The characteristics of shielded pumps are: a fully enclosed design, and a unique structure without shaft seals (only static seals rather than dynamic seals), which ensures that there is no leakage from the unit ； The closed self-circulating structure can transport any medium while ensuring no pollution to the environment ； A brand-new low-speed shielded motor and medium circulation system are employed to ensure low vibration, low noise, and low temperature rise of the unit ； The pump body features a tubular design, with identical inlet and outlet diameters that are aligned on the same line; it can be installed at any position in the pipeline just like a valve, offering convenience, speed, and stability ； No shaft seal, no rolling bearings, maintenance-free, reliable operation ； The use of vibration isolation devices such as vibration pads, isolators, and metal bellows results in less vibration and lower noise ； The unique installation structure **reduces the pump’s footprint, enabling savings of over 40% in infrastructure costs.**