centrifugal pump flow rate , the more susceptible cavitation is.

Cavitation. Because when the liquid pressure near the inlet of the impeller blade is less than or equal to the saturated vapor pressure at the liquid conveying temperature, the liquid vaporizes, and there may be gas dissolved in the liquid at the same time, forming a large number of bubbles, and the bubbles flow with the liquid to the higher pressure in the blade channel and instantaneously condense and collapse. At the moment when the bubble condenses and collapses, the liquid around the bubble quickly rushes into the cavity formed by the bubble condensation, forming a strong local high-frequency and high-pressure water hammer, and the metal surface is eroded due to fatigue.

At the same time, electrochemical corrosion occurs on the metal surface due to the presence of reactive gases such as oxygen and the local high temperatures generated when the bubbles condense. This process is called cavitation.

Factors influencing cavitation.

Factors that affect both liquid pressure and saturated vapor pressure affect the occurrence of cavitation.

influencing factors.

Structural parameters of pump inlet: including the shape of the impeller suction inlet, the width of the blade inlet edge, the position of the blade inlet edge and the shape of the front cover plate.

Pump operating conditions: it includes the flow, head and speed of the pump.

Installation location of the pump: It includes the hydraulic loss of the suction line of the pump and the installation height.

Environmental factors: It includes the atmospheric pressure at the place where the pump is installed.

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The straight phenomenon is the cause of the abnormal sound of the current swing, that is, the flow rate of the inlet is low, and the avoidance measure is to ensure sufficient flow.

When the static pressure of the liquid near the inlet of the blade is equal to or lower than the saturated vapor pressure of the liquid at the output temperature, the liquid will vaporize in that section, creating bubbles. When the liquid containing bubbles enters the high-pressure area of the impeller, the bubbles will condense or burst sharply. Due to the disappearance of the bubble, a local vacuum is generated, and the surrounding liquid and high velocity flow to the space occupied by the original bubble, resulting in a great local impact pressure.

The repeated action of this huge impact force causes the pump casing and impeller to be destroyed, a phenomenon called cavitation.

Proper determination of the installation height of the pump prevents cavitation.

When the flow velocity of the liquid at the inlet of the impeller increases, and the pressure is lower than the saturation pressure corresponding to the operating water temperature, a part of the liquid will evaporate (i.e., vaporize). When the evaporated bubbles enter the area with high pressure, they suddenly condense under pressure, and the surrounding liquid is replenished there, causing a hydraulic shock. This phenomenon is called cavitation.

Due to the continuous local impact, the surface of the material will gradually fatigue and damage, causing the erosion of the metal surface, and then the appearance of large and small honeycomb holes, in addition to the impact caused by the damage to metal parts, it will also produce chemical corrosion, oxidation equipment. The cavitation process is unstable, which will cause the pump to vibrate and produce noise, and at the same time, the bubbles will also block the impeller channel, resulting in a decrease in head, flow rate and efficiency.

Centrifugal pump cavitation hazards.

Cavitation is a phenomenon unique to hydraulic machinery, and it has many serious consequences.

Cavitation causes the overflow parts to be destroyed by erosion;

Cavitation degrades the performance of the pump, and cavitation causes the pump to produce noise and vibration.

Measures to improve the anti-cavitation performance of centrifugal pumps.

1) Improve the anti-cavitation performance of the centrifugal pump itself.

Improving the structure of the pump from the suction inlet to the inlet of the impeller blades The front induction wheel is adopted, and the double-suction impeller is adopted.

The design sink adopts a slightly larger angle of attack.

Cavitation-resistant materials are used.

2}Measures to increase the NPSH of the liquid feed device.

Increase the pressure on the liquid level in the reservoir before the centrifugal pump.

Reduce the installation height of the suction device in front of the pump.

l Change the suction device to the can pouring device.

Reduces flow loss on the front line of the pump.

Cavitation of centrifugal pumps:

When there is air in the centrifugal pump casing, the centrifugal force is less because the density of the air is much less than that of the liquid. Therefore, the pressure difference between the liquid level of the tank and the suction inlet of the pump is not enough to press the liquid in the tank into the pump, that is, the centrifugal pump has no self-priming ability, so that the centrifugal pump cannot transport the liquid, this phenomenon is called "cavitation phenomenon".

To avoid cavitation, the main measures that should be taken:

1. When installing, the distance between the suction port of the pump and the liquid level should be as low as possible to reduce the suction pressure loss.

2. Increase the diameter of the pump suction pipe to reduce the resistance loss of the suction pipeline.

3. In satisfaction.

Under the premise of head and flow requirements, the lower the number of revolutions, the better, to reduce the vacuum of the pump suction inlet.

4. Adopt double-suction pump or add front.

Centrifugal pump of the induction wheel to improve suction conditions.

5. Under the condition that the process conditions allow, avoid the temperature increase of the conveyed liquid and prevent the vaporization of the liquid.

1. When installing, the distance between the suction port of the pump and the liquid level should be as low as possible to reduce the suction pressure loss.

2. Increase the diameter of the pump suction pipe to reduce the resistance loss of the suction pipeline.

3) Under the premise of meeting the head and flow requirements, the lower the number of revolutions, the better, so as to reduce the vacuum of the pump suction inlet;

4) Adopt a double-suction pump or a centrifugal pump with a front-mounted induction wheel to improve the suction conditions;

5. Under the condition that the process conditions allow, avoid the temperature increase of the conveyed liquid and prevent the vaporization of the liquid.

Centrifugal pump cavitation: due to the suction height of the pump is too high or the temperature of the pump inlet medium is too high, so that the pressure in the pump is equal to or lower than the saturated vapor pressure at the temperature of the conveyed liquid, the liquid vaporization, bubble formation, rupture and other processes caused by the erosion phenomenon, called "cavitation" phenomenon, "cavitation" occurs when the liquid due to impact and noise, vibration, so that the flow rate is reduced, and even no liquid is discharged.

The root cause of cavitation in centrifugal pumps is liquid vaporization.

When a liquid is at a certain temperature and the pressure is reduced to the vaporization pressure at that temperature, the liquid produces bubbles. This phenomenon of creating bubbles is called cavitation.

The causes of cavitation in centrifugal pumps are:

The centrifugal pump is installed too much above the suction level.

The atmospheric pressure at the centrifugal pump installation site is too low.

The liquid conveyed by centrifugal pumps is hot.

Cavitation in centrifugal pumps may be due to ().

a.The actual loading height of the centrifugal pump exceeds the maximum allowable installation height.

b.The liquid conveyed may contain empty sand particles.

c.The centrifugal pump did not drain the gas from the pump.

d.There is a leak in the centrifugal pump.

Correct Answer: The actual installation height of the centrifugal pump exceeds the maximum allowable installation height.

The greater the NPSH of a centrifugal pump, the more blind it is ()aCavitation is less likely to occur.

b.The more likely it is to have hollow cavitation.

c.Whether cavitation is susceptible or not is independent of the value of the critical NPSH.

d.It's not boring to say.

Correct answer: The more prone it is to cavitation.

The relationship between the necessary NPSH and the flow rate of the lead heart pump is ()aIt does not matter.

b.The higher the liquid flow, the smaller the required NPSH.

c.The higher the liquid flow, the greater the required NPSH.

d.It's hard to say.

Correct Answer: The higher the liquid flow, the greater the required NPSH.

Hello! 1.The level of the pool is too low and gas is sucked in.

Solution: Increase the pressure on the liquid level in the reservoir before the centrifugal pump. 2.

The installation height of the pump ruler is too high. Solution: Reduce the installation height of the suction device in front of the pump.

3.The flow rate and resistance on the suction line are too great. Workaround:

Change the suction device to a can pouring device. 4.The suction pipe and pressure flange are not well sealed, and air enters.

Solution: Rent a cover to improve the structural design of the suction inlet of the pump to near the inlet of the impeller blades.

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