What is the difference between cavitation and vapor locking in centrifugal pumps?

1. Cavitation: In fluid flow and hydraulic machinery, cavitation often occurs; it can happen in everything from blood flow to turbines and ship propellers. Basic process: When the liquid flow pressure in a certain area of the flow channel drops to a certain limit value (currently, the vaporization pressure is commonly used as this value), bubbles form in the liquid flow. These bubbles filled with gas or steam expand rapidly, and as they move with the liquid flow to areas with higher pressure, they condense and collapse quickly. The entire process that is accompanied by noise, vibration, and even erosion of the flow channel material is known as cavitation. 2. Vapor locking: The “vapor locking” phenomenon in centrifugal pumps occurs when gas is present inside the pump, preventing it from drawing in liquid.

1. Cavitation: At a certain temperature, when the pressure of a liquid is reduced to its vaporization pressure at that temperature, bubbles form in the liquid. This phenomenon of bubble formation is called cavitation. Causes and hazards of cavitation: During pump operation, if the absolute pressure of the liquid being pumped in a certain local area of its flow path (usually somewhere slightly downstream of the inlet to the impeller blades) drops to the vaporization pressure of the liquid at that temperature for some reason, the liquid begins to vaporize there, generating large amounts of steam and forming bubbles. When this liquid containing many bubbles moves forward through the high-pressure areas inside the impeller, the high-pressure liquid surrounding the bubbles causes them to shrink rapidly and eventually burst. As the bubbles coalesce and burst, liquid particles fill the voids at high speeds; this creates a very strong water hammer effect. The impact stress on the metal surface can reach several hundred to several thousand atmospheres, with an impact frequency of tens of thousands of times per second. In severe cases, this can cause the wall thickness to be breached. 2. Air locking: This occurs when the pump is not filled with the liquid to be transported before it is started, or when air gets into the pump during operation. Since the density of gas is lower than that of liquid, the centrifugal force generated is insufficient to expel the air. As a result, the vacuum created at the center of the impeller is not enough to draw liquid into the pump. Even though the impeller keeps rotating, the centrifugal pump loses its self-priming ability and is thus unable to transport liquid; this phenomenon is known as air locking. ——I hope this can help you solve the problem. This post was last edited by ccww2006 on 2009-3-9 at 19:11.]

“The \"cavitation\" phenomenon is an abnormal condition that occurs due to inadequate design of centrifugal pumps or operating conditions that deviate from those designed for them. When the pressure at the inlet of the impeller is equal to the saturated vapor pressure of the medium being transported, the liquid medium will vaporize; its volume expands suddenly, which disrupts the flow of liquid at the impeller inlet. As the liquid carries the bubbles into the impeller, they are compressed; the high pressure causes the bubbles to collapse suddenly. The surrounding liquid then rushes in at high speed to fill the space left by those bubbles, resulting in high local pressures. These pressures continuously strike the surface of the impeller, leading to its rapid damage. “When \"cavitation\" occurs, the pump body vibrates, noise levels increase, and the pump’s flow rate and pressure drop significantly. The solution is 1: select an adequate net positive suction head. 2. Promptly adjust abnormal operating conditions, such as the cooling medium or the inlet pressure. :Lol, the \"air locking\" phenomenon occurs when there is gas inside the pump at the time of startup. Since the density of gas is much lower than that of liquid, the centrifugal force generated by the rotating impeller is very small, and the negative pressure created at the center of the impeller is insufficient to draw liquid into that area; as a result, the medium cannot be transported. Solution: Use a pumping method to force the gas out :)

The methods to avoid cavitation generally involve increasing the flow rate of the water pump, raising the inlet pressure of the water pump, and lowering the inlet temperature of the water pump； methods such as

It might be cavitation – is your water temperature prone to vaporization at this pressure? The feeling of being restrained by gas is incredible!

Gas entrapment refers to the situation where flow rate is reduced due to the presence of gas in the medium; centrifugal pumps generally need to have their gas removed before starting； Cavitation refers to the phenomenon of vaporization that occurs at the inlet of a pump when the pressure there is too low or the temperature is too high, resulting in a pressure lower than the saturated vapor pressure under those conditions. Cavitation poses significant hazards, and it is accompanied by noises and pressure fluctuations.

Cavitation phenomenon: When liquid containing bubbles enters the impeller, the bubbles coalesce due to the increase in pressure. The disappearance of the bubble creates a local vacuum, causing the surrounding liquid to rush toward the center of the bubble at high speed, resulting in shock waves and vibrations. Especially when the accumulation of bubbles occurs near the surface of the blade, numerous liquid particles strike the blade; furthermore, the bubbles may contain some oxygen that causes chemical corrosion of the metal material. Operating in such conditions for an extended period will lead to premature damage of the blade. When a pump operates under cavitation conditions, it vibrates and produces noise; its flow rate, head, and efficiency all decrease significantly, and in severe cases it may even fail to draw in liquid. To avoid cavitation, the pump should not be installed too high, so as to ensure that the pressure throughout the impeller is higher than the vapor pressure of the liquid. Air entrapment phenomenon: When the pump is in operation, negative pressure often exists in the suction pipeline and at the axis of the pump. If the sealing of the pipeline and shaft seal is poor, air will leak in, causing the average density of the fluid inside the pump to decrease. If this decrease in average density is severe, the pump will be unable to draw in liquid.

If there is cavitation, the pressure will drop. It doesn’t seem like cavitation based on what you’ve described; you should check the flow rate. If there’s no problem with that, then it’s a mechanical issue

It’s probably not a mechanical issue; the noise disappears when I turn on the pump’s drain valve a little. So, vapor entrapment only occurs when the pump is running, while cavitation appears during the operation of the pump? Can it be understood that way?

If the pump is evacuated, air locking can also occur

As a supplementary note, cavitation can cause damage to pump equipment, whereas vaporization itself does not cause any damage to the equipment. Equipment managers must absolutely prevent cavitation from occurring.

Are you aware of the pump vibration? It should be cavitation. Try lowering the temperature.

Level 8? ? 8 impellers? The pressure isn’t that high

Cavitation: 1. Reduce the pump’s installation height; 2. Consider using parallel pumps to increase flow rate; 3. Adjust the pump’s pressure and temperature. Gas entrapment: Fill the pump to prevent it from running dry

I believe it is not cavitation, because whatever causes cavitation, both the flow rate and outlet pressure will decrease. Measures to eliminate cavitation: 1. In terms of pump design, the allowable cavitation head should be reduced as much as possible, thereby allowing for an increase in height. 2. In terms of the design of the suction pipe, minimize the losses in the suction pipeline as much as possible ； Reduce the actual installation height. 3. From the operational perspective: reduce the temperature of the conveying medium ； Reduce the head loss in the suction pipeline (close the pump’s discharge valve to decrease the system flow rate) ； Increase the pressure at the liquid level of the inhalant. It’s just my personal opinion; I’m not sure if it will be helpful to you.