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1. Sealing packing. This packing seal has a simple structure and requires an appropriate level of tightness; as a result, there is some leakage. It is generally used in environments with non-polluting media. Moreover, the axial compressive force is uneven, which leads to rapid wear of the packing at the gland area. Therefore, it is rarely used in chemical centrifugal pumps these days. 2. Mechanical seal. Mechanical seals achieve sealing by means of a pair or several pairs of end surfaces that slide relative to each other perpendicular to the shaft; the elasticity (or magnetism) of hydraulic and compensating mechanisms is used to keep these surfaces in contact. Sealing between the rotating ring and the stationary ring is achieved through an appropriate compressive force (specific pressure) generated by elastic elements (springs, bellows, etc.) and the pressure of the sealing fluid. This force creates a proper compression on the contact surfaces (end faces) of the rotating and stationary rings; the flat end faces are in close contact with each other, with a very thin layer of liquid existing between them, thereby enabling sealing. This membrane exerts both hydrodynamic and hydrostatic effects, serving to balance pressures and lubricate the end surfaces. The end face must be highly flat in order to ensure perfect fit between the end faces, thereby achieving uniform specific pressure, that is, relative rotary sealing. 3. Seal with dry air. Generally, a typical dry gas seal structure includes components such as a static ring, a dynamic ring assembly (rotating ring), secondary sealing O-rings, a static seal, and a spring seat (cavity). In the stainless steel spring seat, the static ring and O-ring provide secondary sealing. When sealed, the spring brings the stationary ring into alignment with the moving ring assembly fixed to the rotor. Key points for using dry gas seals: It is essential to ensure a gas supply between the two sealing surfaces; a loss of this gas supply during rotation will inevitably lead to seal damage. 4. Floating ring seal. High-pressure seal oil is used to create an oil film between the floating ring and the shaft sleeve, thereby throttling and reducing pressure and preventing flow from the high-pressure side to the low-pressure side, and thus stopping gas flow toward the low-pressure side. Due to the main function of the oil film, it is also known as oil film sealing. The forces acting on the floating ring during operation are similar to those in bearings; the difference is that in bearings it is the shaft that is lifted. In the case of floating ring seals, since the weight of the floating ring is very small, when the shaft rotates and an oil film buoyancy is generated in the gap between the floating ring and the shaft, an oil film buoyancy also arises in that gap. According to the principle of the supporting oil film, if the floating ring is perfectly coaxial, no buoyancy from the oil film will be generated. However, if the floating ring is eccentric with respect to the shaft, an oil film buoyancy will be created during rotation, which causes the floating ring to rise and reduces the eccentricity. When the eccentricity is reduced to a certain level, such that the resulting buoyant force is exactly equal to the weight of the floating ring, dynamic equilibrium is achieved. Because the floating ring is very light, the eccentricity in this dynamic balance is extremely small; in other words, the floating ring can essentially remain basically concentric with the shaft. The seal of a centrifugal pump is not a perfect seal (which is a necessary condition for magnetic drive pumps). According to API standards, there is a slight leakage per hour. This leakage occurs because, under actual operating conditions, the liquid enters the friction surfaces; as it carries away heat, it also pulls some liquid with it from the rotating and stationary rings, and this liquid then leaks out.