Water Cavity Vacuum Pump Cavitation Principle and Prediction

1, the principle of water ring vacuum pump cavitation cavitation is caused by liquid gasification, the liquid molecules escape the liquid name, into the gas molecules inside, known as "gasification." Liquid gasification level and the size of the pressure, heat up and down nothing to do. Gas dissolved in the liquid, the pressure and heat changes will also be released into the formation of cavitation. When the liquid pressure outside the province rises below the saturation vapor pressure of the liquid in the heat, forming bubbles or cavities in all the sea; and the central bubble in the pressure is suddenly crushed by the pressure of four, the flow due to flexibility to Extremely high progress squeezed to the bubble core, resulting in a hydro-charged facility. This microbubble production, rupture, and over-current nominal physical and chemical effects of the entire inside called cavitation. Cavitation generated when the bubble is fixed to a low pressure Department, the volume decreases resulting in disillusionment. This disappearance of pressure due to pressure bubbles in the liquid scene known as cavitation collapse.

Vacuum pump in operation, if all over the flow of the entire sea area (usually impeller blade inlet somewhere later) that kind of cause, the relative pressure of the liquid pumped up to the subsequent heat of liquid gasification pressure, the liquid will At the end of the gasification, resulting in a large number of steam to form bubbles, when the liquid containing a large number of bubbles forward through the low pressure region within the impeller, the bubbles around the low-pressure liquid so that the bubble suddenly enlarged resulting rupture. In the same burst of bubble condensation, the liquid particles filled with holes at a high rate of progress, in this moment has a very strong water hammer effect, and a high charge of the efficiency of combat strikes against the non-metallic name, charge up to hundreds of thousands of stress collapse thousands A barometric pressure, strikes into the array efficiency of tens of thousands of times per second, will break the wall thickness.

Produced in the vacuum pump 怄 bubble and bubble rupture overcurrent element is destroyed inside the vacuum pump in the cavitation within. After the cavitation generated by the vacuum pump, unless it damages the overcurrent element, noise and vibration will also occur and the performance of the pump will increase. In severe cases, the liquid in the pump will be suspended and the normal operation will not be allowed.

Cavitation erosion of water ring pumps is in the bubble generation and rupture parts, non-metallic nominal pitting scene, significant honeycomb corruption. Then the air pump impeller in the cavitation site have greater residual stress, but also lead to stress release, resulting in cracks. Because of the sudden cavitation of bubbles in the low-pressure zone during pump cavitation and the noise and vibration associated with strong water strikes, it is possible to hear crackling sounds like popcorn. Then the bubble in the name of non-metallic rupture, non-metallic name will be one after another intense water hammer emerge, non-metallic grains loose and exfoliated honeycomb or even perforation. Cavitation damage in addition to mechanical effects, but also with the electrolytic, chemical erosion and many other simple role. The motivation for the theory of destruction shows that the cavitation damage caused by the pump overcurrent element is exactly where the bubbles disappear. Vacuum pumps require liquid as the working medium. Each liquid has a corresponding saturated vapor pressure at a certain heat level. When the relative pressure of the inhalation area is closer to the saturated vapor pressure of the liquid, the liquid becomes more and more vaporizable. At that time, a large number of bubbles were created in the name of the working fluid aspirated into the sea area, because the liquid vapor generated in the working chamber would occupy the space of the whole working chamber and the suction capacity of the pump would be increased. When the suction pressure of the sea reaches the saturated vapor pressure of the working fluid, it can be considered that the working chamber is fully flooded with the working liquid vapor. At this time, the external suction power of the pump is near zero, and the cavitation of the pump is also the most significant.

Then the working fluid is water, the higher the water temperature, the more the pump suction performance. Water ring vacuum pump water temperature on its performance is not greater, while the water ring vacuum pump performance curve are measured at 15 ℃ water temperature, so the theory of choice water ring vacuum pump response water ring vacuum pump suction rate continue to be modified.

2, water ring vacuum pump cavitation scene of the steps to eliminate and prevent the water ring vacuum pump cavitation in a short time work, will cause the pump noise, vibration becomes larger, and even cause damage to the pump, and therefore should prevent heavy volume water ring vacuum pump in the steam Eclipse state operation, through the following steps:

(1) increase the heat of the water because the vacuum pump freezing water temperature will lead to a significant increase in its pumping, vacuum seal sealing water vapor temperature must be lower than the corresponding saturation heat, or will make the vacuum turn better, but also Will cause the vacuum pump impeller cavitation corruption. Thus raising the heat of the water to prevent cavitation motivation.

(2) The popularization and selection of the correctness of the vacuum pump to run in the selection of the insurance phase, the choice of vacuum suction pressure and water heat should avoid the vacuum pump easily produce cavitation pressure scale, that is to prevent the vacuum pump in the critical vacuum Or critical discharge pressure of the sea operation, heavy volume increase the production of cavitation.

(3) device cavitation shield tube device with a cavitation shield tube of the vacuum pump, cavitation bubbles generated in the middle of the rupture within the compression, the introduction of high pressure from the inside of the non-condensable gas can be added in time due to the emergence of bubble rupture Of space, that can greatly increase the damage of the pump on the cavitation and increase noise and vibration caused by cavitation.

Some pumps have a cavitation shield interface, such as operating at ultimate pressure, opening the cavitation shield connection (or coupling with a soda filter) to remove cavitation noise and to continue with the pump while maximizing inspiratory motivation cover.

(4) with the air ejector The role of the air ejector is the use of atmospheric pressure absolute vacuum pump pressure, resulting in jet of air in the ejector than the vacuum pump lower suction pressure to eliminate the vacuum pump ultimate pressure to prevent vacuum pump cavitation , Play a role in shielding the vacuum pump. Because the air ejector is designed to prevent cavitation of the vacuum pump and cover the vacuum pump, a vacuum pump normally equipped with an air ejector is preferable in that the vacuum formed by the suction is better than that not provided.

(5) The lower saturated steam liquid is used as the working fluid to change the working fluid from original water to transformer oil, and the ultimate vacuum loss due to lower saturated vapor pressure of the oil loses higher promotion. In the removal of large gas purification and in some extraordinary occasions, the working fluid of the vacuum pump can also be used other liquids (available propanol, ethanol, xylene, aniline, such as amphetamine hydrochloride viscosity lower organic solvents) , The ultimate vacuum is determined by the saturated vapor pressure of the working fluid.

Oil ring vacuum pump at 20 ~ 90 ℃ operation, so its gas in the extraction of steam and other gases due to higher temperatures, the steam is not easy to aggregate, so the pump oil is not easy to be emulsified, which popularized the life of pump oil. The use of organic solvents as a working fluid, should pay attention to whether the explosion-proof motor, the vacuum pump and seal erosion problems.

(6) pump impeller, disc and so on to adopt the anti-cavitation power of the opposite information anti-cavitation power has a very clear distinction. Information on the anti-erosion power of the composition of a lot of information, there is usually high hardness and high elasticity of anti-erosion power is stronger. Overseas recommended low-carbon chromium-nickel alloy steel, such as 13Cr4N as a cavitation in the operation of hydraulic machinery, there is better anti-corrosion performance. Compared to the impeller coating steps rarely used, non-metallic coatings coated with epoxy resin, nylon powder, polyurethane and so on. Nominal surfacing alloy or spray alloy in the runway to prevent cavitation damage has also been given certain motives, such as stainless steel wire surfacing welding method, stainless steel plate inlaid welding repair method, alloy powder spray welding.

Non-metallic and non-metallic alloys (including stainless steel) compared to the number of steps, non-metallic coatings in the form of economy, but should be mastered in its operating procedures to prevent coating shedding. Adoption of alloy powder welding motivation but high profits, and some central may no longer continue.

3, the end of the vacuum pump cavitation is a common vacuum pump failure, any vacuum pump will have cavitation. In the daily life of brick and tile enterprises, doing a good job of the fundamental protection of facilities, there is a vague awareness of the vacuum pump cavitation, and proper steps to prevent cavitation, will certainly be able to achieve the goal of aggravating the vacuum pump cavitation.

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