渣浆泵的汽蚀现象怎么发生的与防止

什么是汽蚀现象呢?可以从日常生活来谈起:如果在一个大气压力作用下，将水加热到100°C就会有大量气泡从水中析出——水沸腾了。但是在高山上，由于空气稀薄而气压低，水不到100C就会冒出大量气泡。如果水面压力降低到0. 024atm以下时，水在20C的常温下也会冒出大量的气泡，水沸腾。所以水的汽化不但与温度有关，而且还与压力有关。在一一定温度下，液体开始汽化的临界压力叫做汽化压力(或称饱和蒸汽压力)，用p，表示。水在各种温度下的汽化压力P，见表1-1和表1-2，其他液体在各种温度下的汽化压力p,如图3- 1所示。
    从离心泵的工作原理中知道，泵能将低处的液体吸上来是由于叶轮转动产生离心力，使泵的进口处压力降低产生真空，也就是低于大气压力，而吸水池的液面上有一个大气压力，在其作用下把液体压上来了。如果泵的安装离吸入液面越高，则泵的进口的压力要求更低，真空度更大，才能把液体吸上来。当泵进口处的压力低至该温度下该液体的汽化压

力时，虽然在常温下，该液休也会汽化而产生大量气泡，这些气泡随液体一起流入叶轮流道中。由于泵通过旋转的叶轮对液体作功，使液体能量逐渐增加，液体的压力又逐渐升高，液体中的气泡受压破裂，重新凝结成液体而消失。这时，气泡四周的液体质点以很高的速度运动补充，质点互相撞击，在瞬间产生很高的压力(即水锤现象)，产生很强的水击波就像无数个小弹头连续打击叶片表面，久而久之，金属表面逐渐因疲劳破坏，在叶片上产生蜂窝状的小块剥落，通常称为剥蚀。在所产生的气泡中，还有一些活泼气体( 如氧等)，借助气泡凝结时所放出的热量对金属起化学腐蚀、电化腐蚀与机械剥蚀的共同作用，加快了对金属的损坏速度，这种现象就叫做汽蚀现象。
    泵开始发生汽蚀时，气泡较少，区域也较小，对泵的正常工作没有明显影响，但当发展到一定程度时，就会影响到泵的性能(流量、扬程、功率、效率)明显下降(泵的汽蚀试验就是利用这一现象进行判断)， 并发生振动、噪声。当汽蚀进一步发展，气泡大量产生就会造成性能曲线急剧下降(图3-2)，液体产生断流而泵无法工作。所以泵的汽蚀问题必须应予重视与防止。

渣浆泵厂家

How to prevent cavitation of slurry pump

What is cavitation? We can start from our daily life: if water is heated to 100 ° C under the action of an atmospheric pressure, a large number of bubbles will come out of the water - the water will boil. But in the high mountains, because the air is thin and the air pressure is low, a lot of bubbles will appear when the water is less than 100C. If the water pressure drops below 0.024atm, a large number of bubbles will appear and the water will boil at 20c. So the vaporization of water is not only related to temperature, but also to pressure. At a certain temperature, the critical pressure at which the liquid begins to vaporize is called the vaporization pressure (or saturated steam pressure), which is expressed as P. See Table 1-1 and table 1-2 for the vaporization pressure P of water at various temperatures, and Figure 3-1 for the vaporization pressure P of other liquids at various temperatures.

From the working principle of centrifugal pump, it is known that the pump can suck up the liquid at the low position because the centrifugal force is generated by the rotation of the impeller, which reduces the pressure at the pump inlet and generates a vacuum, that is, the pressure is lower than the atmospheric pressure, and there is an atmospheric pressure on the liquid surface of the water suction tank, under the action of which the liquid body is pressed up. If the installation of the pump is higher than the suction liquid level, the pressure requirement of the pump inlet is lower and the vacuum degree is greater, then the liquid can be sucked up. When the pressure at the pump inlet is low to the vaporization pressure of the liquid at this temperature

In case of force, although at normal temperature, the liquid will also vaporize and generate a large number of bubbles, which will flow into the impeller passage together with the liquid. Because the pump works on the liquid through the rotating impeller, the liquid energy increases gradually, the pressure of the liquid increases gradually, and the bubbles in the liquid break under pressure and condense into liquid again and disappear. At this time, the liquid particles around the bubble move at a very high speed to supplement each other, and the particles collide with each other, generating a very high pressure (i.e. water hammer phenomenon) in an instant, and generating a strong water shock wave is like countless small warheads hitting the surface of the blade continuously. Over time, the metal surface gradually suffers from fatigue damage, resulting in honeycomb like small pieces of peeling off on the blade, which is usually called denudation. In the generated bubbles, there are also some active gases (such as oxygen, etc.), with the help of the heat released when the bubbles condense, they play a joint role of chemical corrosion, electrochemical corrosion and mechanical erosion on the metal, accelerating the speed of metal damage, which is called cavitation phenomenon.

When cavitation occurs at the beginning of the pump, there are fewer bubbles and smaller areas, which has no obvious impact on the normal operation of the pump. However, when it develops to a certain extent, it will affect the performance of the pump (flow, head, power, efficiency) significantly reduced (the cavitation test of the pump is to use this phenomenon for judgment), and vibration and noise will occur. When cavitation develops further, a large number of bubbles will cause a sharp decline in performance curve (Fig. 3-2), resulting in fluid cut-off and the pump can not work. Therefore, the cavitation problem of pump must be paid attention to and prevented.

Slurry pump