Four sealing modes of centrifugal pump:

To put it simply, the seal of a centrifugal pump is a moving ring that moves along with the axis, and a static ring that is static relative to the shell, which is pressed together by a spring force. As for the structure, other manufacturers have already mapped it. It will not be repeated, just like two hands gluing them together and putting them in the water. The palm of the hand can still do the work. The moving ring rotates with the shaft and is close to the static ring wall. Therefore, the liquid is closed from one side to the other. As for the working principle, it is with the centrifugal pump front and rear seal bushing (the factory is basically mouth ring), with the gap between the shell seal bushing and the impeller seal bushing to control a small amount of leakage, but the mechanical seal is better.

1. Packing seal
The packing seal has a simple structure and appropriate tightness, so there will be a certain leakage, which is generally used under the condition of non-polluting medium, and the axial compression force is uneven, the packing wear is fast at the gland, and the chemical centrifugal pump is rarely used at present.

2. Mechanical seal
The mechanical seal keeps fit through one or more pairs of relative sliding end faces perpendicular to the shaft under the action of the elasticity (or magnetic force) of the hydraulic and compensation mechanism to assist the seal. The seal between the moving ring and the static ring: it depends on the appropriate compression force (specific pressure) produced by the elastic element (spring, bellows, etc.) and the sealing fluid pressure, a suitable compression force is produced on the contact surface (end face) of a relatively moving moving ring and static ring, a flat end face is closely fitted, and a very thin liquid film is maintained between the end faces, thus realizing the seal. The film has the functions of hydrodynamic pressure and static pressure, which can balance the pressure and lubricate the end face. The end face must be highly flat, so that the end face has perfect fit, so that the specific pressure is uniform, that is, the relative rotary seal.

3. Dry air seal
Generally speaking, the typical dry gas seal structure includes static ring, moving ring assembly (rotary ring), secondary seal O-ring, static seal, spring seat (cavity) and other parts. In the stainless steel spring seat, the static ring and O-ring are sealed with secondary seals. When sealed, the spring matches the static ring with the moving ring assembly fixed on the rotor.
Key points for the use of dry gas seal: the gas source between the two secret covers must be ensured, and the loss of gas source during rotation will inevitably cause seal damage.

4. Floating ring seal
The high-pressure sealing oil is used to form an oil film between the floating ring and the shaft sleeve to throttle and reduce the pressure to prevent the high-pressure side from flowing to the low-pressure side, thus preventing the gas from flowing to the low-pressure side. Because of the main role of oil film, it is also called oil film seal. The force acting on the floating ring is similar to that of the bearing, except that the bearing floats the shaft. For the floating ring seal, because the weight of the floating ring is very small, when the shaft rotates and produces oil film buoyancy in the gap between the floating ring and the shaft, oil film buoyancy will be produced in the floating ring and shaft gap. According to the principle of supporting oil film, if the floating ring is completely coaxial, it will not produce oil film buoyancy. For example, if the floating ring is eccentric with the shaft, it will produce oil film buoyancy when rotating the shaft, which makes the floating ring float and reduce the eccentricity. When the eccentricity is reduced to a certain extent, that is, the corresponding buoyancy is exactly equal to the weight of the floating ring, the dynamic balance is achieved. Because the floating ring is very light, the eccentricity in this dynamic balance is very small, that is, the floating ring can basically remain concentric with the axis.

The centrifugal pump seal is not completely sealed (this is a necessary condition for the existence of the magnetic pump), according to the API standard, there will be a small amount of leakage every hour, this kind of leakage, because in the actual working conditions, the liquid enters the friction surface and takes away the heat, at the same time, some liquid is taken out by the moving ring, and these liquids will leak out.