How does the pump cavitation occur, and how does a centrifugal pump cavitation occur

The installation of centrifugal pump depends on the height of the centrifugal pump cavitation has occurred, and the occurrence of cavitation of centrifugal pump is closely connected with the vaporization of the liquid is transferred, so it should be a special case of &mdash when the vaporization of the liquid; — boiling and boiling liquid. When the surface pressure of — — saturated vapor pressure. Health level self-priming pump

How does a centrifugal pump cavitation occur: in daily life, when the water is heated to 100'C, the water boils and turns into vapour into the atmosphere. As the altitude rises, the boiling temperature of the water will decrease. This is due to the gradual thinning of the air with the elevation of altitude, the decrease of the concentration of air molecules on the water surface, and the decrease of the atmospheric pressure. The pressure formed by the water molecules escaping from the water is closer to the atmospheric pressure. When the pressure of water vapor is equal to that of air pressure, the water will boil. So when the liquid is boiling at a certain temperature, the pressure above the liquid level is called the saturated vapor pressure of the liquid at this temperature.

It should be clear that for all kinds of liquids, their gasification rate, boiling temperature and pressure are also different due to their different properties, so their saturated vapor pressure is also different.

In Figure 239, the centrifugal pump the liquid from the tank can suck it up, because of the pressure tank is Pi on the surface of the atmospheric pressure Po and centrifugal pump at the presence of population pressure difference (Po-P.). Normally, atmospheric pressure. For one constant, if the upper sucking height is on the day. The higher, the larger the flow, the suction pipe. The greater the resistance, the smaller the pressure of the pump population, but the drop of sound is limited. When the pressure of the impellers is at the population, the saturated vapor pressure of the conveyed liquid at working temperature is p. When the partial vaporization of liquid will generate bubbles with the liquid from the pump entrance into the impeller into the impeller, under the action of centrifugal force, with the pressure increasing, the sharp contraction, bubble condensation, make the surrounding liquid at high speed toward the original bubble space, impeller cavitation by figure 2-40 damage

High intensity shock waves, impellers and pump shells, produce noise, and cause vibration.

The impact force produced by the collapse of the bubble for a long time as well as in the liquid

The chemical corrosion effect of dissolved oxygen on metals, and the local surface of the impeller.

Cracks, even spongy damage, are called cavitation.

Figure 240 is shown as an impeller damaged by cavitation.

If the centrifugal pump continues to operate when cavitation occurs, the existence of bubbles will cause the flow rate of the centrifugal pump to drop. Meanwhile, the pump's lift and rescue rate will also decrease rapidly, which will destroy normal operation. Figure 2— the solid line of 41 is the performance curve of the pump when it works normally. The part of the dotted line is cavitation.

After the performance curve.

    To avoid the occurrence of centrifugal pump cavitation, the absolute pressure of impeller population must be higher than the saturated vapor pressure of liquid under working temperature, and the absolute pressure of pump population should be higher. The centrifugal pump usually needs to pass the experiment before going out to determine the conditions of cavitation erosion at a certain flow rate and a certain atmospheric pressure, and stipulate a characteristic parameter &mdash, &mdash, which allows the pump to resist cavitation, and allow the allowance of cavitation.

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