答：风机喘振，顾名思义就象人哮喘一样，风机出现周期性的出风与倒流，相对来讲，轴流式风机更容易发生喘振，严重的喘振会导致风机叶片疲劳损坏。
风机出现喘振的现象：
1、风机声音异常噪声大、振动大、机壳温度升高、引送风机喘振使炉膛负压波动燃烧不稳。
2、电流减小且频繁摆动、出口风压下降摆动。

原因：
1、两风机并列运行时导叶开度偏差过大使开度小的风机落入喘振区运行。
2、烟风道积灰堵塞或烟风道挡板开度不足引起系统阻力过大。
3、风机长期在低负荷运转。
处理方法:
一般的处理原则是调整负荷、并列运行风机负荷应相近，再根据上面所说的可能原因进行查找，再作相应处理。

1、现象：电流减小且频繁摆动、出口风压下降摆动。风机声音异常噪声大、振动大、机壳温度升高、引送风机喘振动使炉膛负压波动燃烧不稳。

2、原因：烟风道积灰堵塞或烟风道挡板开度不足引起系统阻力过大。；两风机并列运行时导叶开度偏差过大使开度小的风机落入喘振区运行（我们常碰到的情况是风机导叶执行机构连杆在升降负荷时脱出，使两风机导叶调节不同步引起大的偏差）；风机长期在低出力下运转。

3、处理方法：调整负荷、关小高出力风机的导叶开度使风机出力相近，减小负荷量的变化率，加强进风段和出风段的风压探测和信息反馈控制，再根据上面所说的可能原因进行查找再作相应处理。

预防措施：

1、使泵或风机的流量恒大于QK。如果系统中所需要的流量小于QK时，可装设再循环管或自动排出阀门，使风机的排出流量恒大于QK. ;

2、如果管路性能曲线不经过坐标原点时，改变风机的转速，也可能得到稳定的运行工况。

3、对轴流式风机采用可调叶片调节。当系统需要的流量减小时，则减小其安装角，性能曲线下移，临界点向左下方移动，输出流量也相应减小。

4、*根本的措施是尽量避免采用具有驼峰形性能曲线的风机，而采用性能曲线平直向下倾斜的风机。

　　风机喘振的判断方法

　　1. 听

　　通风机在稳定运转的正常工况下，其噪声较低，而且是连续性的。当接近喘振工况时，由于整个系统产生气流周期性振荡，因而在出气管道中气流发出的噪声也时高时低，并产生周期性的变化。进入喘振工况时，噪声立即大大增加，甚至有爆音出现。

　　2. 看

　　观测通风机出口的压力和流量。通风机在稳定工况下运行时，其出口压力和进口流量的变化不大，也有规律，且所测的数据在平均值附近摆动，变动的幅度很小;当接近进入喘振工况时，二者变化都很大 。

　　观测机体和轴承的振动情况。当接近进入喘振工况时，风机轴承座将发生强烈的振动，出口管道也会出现强烈的振动 。

　　2、防止喘振的方法

　　1. 风机选型时，其性能要在高效区内。

　　不要人为地随意增加选型系数，而使风机在实际运行中的实际流量远远高于设计流量，若采用大量节流，就很容易把风机调节到喘振区域工作。

　　为此，在风机设计和选型中，要避免工况范围接近进入喘振区。例如 , 在循环流化床风机的选型中，一般设计院给出两个参数点TB、BMCR。TB是锅炉大负荷点，BMCR点为设计运行点，TB点的性能取BMCR点的15%～30%。在选型中二者必须都要考虑，使风机既能在BMCR点进入稳定工况区运行，又可达到TB点。

　　掌握了这些，就可以使BMCR点在高效区运行，要把TB点定位到低效区内，因为风机一般情况下不在此点运行。所以，掌握和了解喘振的特性尤为重要。

　　2. 风机在系统运行中一旦发生喘振，还可以通过改变风机转速的方法来调整工况范围。

　　离心通风机可以改变叶轮直径，轴流通风机可以改变动叶安装角，这些方法都可以使通风机的性能曲线向小流量区域移动 , 这时喘振临界线也就相应地向小流量区域移动，这同样也可以扩大通风机的稳定工况范围 。

　　3. 由于某些工作场合均不具备上述调节条件，也不能停车而影响生产，所以还有一种简单快捷的调节方法也可消除喘振，这就是加设放气阀。

　　以使Q=Q放 +Q喘振 >Qmin，就马上可以消除喘振。但必须得指出放入大气的气体应是无害气体，若是有害气体就必须得由小管道引入通风机进口管道中。这种方法的缺点是，会将经过叶轮获得的动量白白放掉一部分，从而使风机整体效率下降。但因其方法简单且*，在通风机调节中被广泛地应用 。

　　4. 两阀操作法。

　　在通风机的排气管道上设两个阀，把两个阀之间的容积固定为某一值，两个阀之间的容积相当于一个储气罐，*阀直接装在离风机出口较近的位置上，相当于一个节流阀，稍微节流就可以防喘振;而第二个阀仅作为一个阻力。实践证明，这种装置不仅可以达到系统的稳定运行，对减小噪声也很有利。

　　5. 防喘振环。

　　目前在地铁或隧道用风机设备中，在主风筒加设防振环已成为普遍趋势。这种导流片可在气流出现旋转脱离时，不是经过叶道产生非稳定气流团，而是沿着导流片逆向流回叶片。缺点是在此情况下部分气流做了无用功，但它可以使风机的稳定工况范围扩大，喘振区域缩小！

　　喘振是指风机出现周期性的出风与倒流，相对来讲，轴流风机更容易发生喘振，严重的喘振会导致风机叶片疲劳损坏。

      风机出现喘振的现象：

　　(1)风机声音异常，噪声大、振动大、机壳温度升高，引、送风机喘振使炉膛负压波动燃烧不稳。

　　(2)电流减小且频繁摆动、出口风压下降摆动。

　　常见的原因：

　　(1)两风机并列运行时导叶开度偏差过大使开度小的风机落人喘振区运行。

　　(2)烟风道积灰堵塞或烟风道挡板开度不足引起系统阻力过大。

　　(3)风机长期在低负荷运转。处理原则：一般是调整负荷、并列运行风机负荷应相近，再根据上面所说的可能原因进行查找，再做相应处理。

　　A: Fan surge, just as the name suggests, is like human asthma. The fan has periodic air outlet and backflow. Relatively speaking, axial flow fans are more prone to surge. Serious surge will lead to fatigue damage of fan blades.

　　Surge of fan:

　　1. Abnormal fan sound, high noise and vibration, increased casing temperature and surge of induced draft fan make furnace negative pressure fluctuate and combustion unstable.

　　2. The current decreases and swings frequently, and the outlet wind pressure drops and swings.

　　reason:

　　1. When the two fans operate in parallel, the guide vane opening deviation is too large, which means that the fan with small opening falls into the surge zone for operation.

　　2. The system resistance is too large due to dust accumulation in the flue and air duct or insufficient opening of the flue and air duct baffle.

　　3. The fan operates at low load for a long time.

　　Treatment method:

　　The general treatment principle is to adjust the load, and the load of parallel running fans should be similar, and then find out the possible causes according to the above, and then deal with them accordingly.

　　1. Phenomenon: the current decreases and swings frequently, and the outlet wind pressure drops and swings. Abnormal fan sound, high noise and vibration, increased casing temperature and surge vibration of induced draft fan make furnace negative pressure fluctuate and combustion unstable.

　　2. Cause: the system resistance is too large due to dust accumulation in the flue and air duct or insufficient opening of the flue and air duct baffle.; When the two fans are running in parallel, the guide vane opening deviation is too large, which means that the fan with small opening falls into the surge zone for operation (we often encounter the situation that the connecting rod of the fan guide vane actuator disengages when lifting and lowering the load, which causes large deviation due to the asynchronous adjustment of the two fan guide vanes); The fan operates under low output for a long time.

　　3. Treatment method: adjust the load, turn down the guide vane opening of the high output fan to make the fan output similar, reduce the change rate of the load, strengthen the wind pressure detection and information feedback control of the air inlet section and the air outlet section, and then find out the possible causes mentioned above before making corresponding treatment.

　　Phenomenon, cause and treatment of fan surge?

　　Precautions:

　　1. Make the flow of pump or fan constant greater than QK. If the required flow in the system is less than QK, a recirculation pipe or an automatic discharge valve can be installed to make the discharge flow of the fan constant greater than qk;

　　2. If the pipeline performance curve does not pass through the coordinate origin, changing the fan speed may also obtain a stable operating condition.

　　3. The axial flow fan is adjusted by adjustable blades. When the flow required by the system decreases, the installation angle will be reduced, the performance curve will move down, the critical point will move to the left and down, and the output flow will decrease accordingly.

　　4. The most fundamental measure is to try to avoid using the fan with hump shaped performance curve, and use the fan with straight and downward inclined performance curve.

　　Judgment method of fan surge

　　1. listen

　　Under the normal working condition of stable operation, the noise of the ventilator is low and continuous. When approaching the surge condition, because the whole system produces periodic oscillation of the air flow, the noise emitted by the air flow in the outlet pipe is also high and low, and has periodic changes. When entering the surge condition, the noise immediately increases greatly, and even there is a popping sound.

　　2. look

　　Observe the pressure and flow at the fan outlet. When the fan operates under stable working conditions, its outlet pressure and inlet flow change little and regularly, and the measured data swing around the average value, with a small range of change; When approaching the surge condition, both of them change greatly.

　　Observe the vibration of engine block and bearing. When approaching the surge condition, the fan bearing pedestal will have strong vibration, and the outlet pipe will also have strong vibration.

　　2. Methods to prevent surge

　　1. when selecting the fan, its performance shall be within the high efficiency zone.

　　Do not artificially increase the type selection coefficient, so that the actual flow of the fan in actual operation is much higher than the design flow. If a large amount of throttling is adopted, it is easy to adjust the fan to the surge area.

　　Therefore, in the fan design and type selection, it is necessary to avoid the operating range approaching the surge area. For example, in the selection of circulating fluidized bed fan, the general design institute gives two parameter points TB and BMCR. TB is the boiler high load point, BMCR point is the design operation point, and the performance of TB point is 15% ~ 30% of BMCR point. Both of them must be considered in model selection, so that the fan can not only enter the stable working condition area at BMCR point, but also reach TB point.

　　After mastering these, we can make the BMCR point operate in the high-efficiency area. We should locate the TB point in the low-efficiency area, because the fan generally does not operate at this point. Therefore, it is particularly important to master and understand the characteristics of surge.

　　2. in case of surge of the fan during system operation, the working condition range can be adjusted by changing the fan speed.

　　The centrifugal fan can change the impeller diameter, and the axial fan can change the installation angle of the moving blade. These methods can make the performance curve of the fan move to the small flow area. At this time, the critical boundary of surge will move to the small flow area accordingly, which can also expand the range of stable working conditions of the fan.

　　3. since some workplaces do not have the above adjustment conditions, and the production can not be affected by shutdown, there is another simple and fast adjustment method to eliminate surge, which is to add a vent valve.

　　So that q=q release +q surge >qmin, surge can be eliminated immediately. However, it must be pointed out that the gas put into the atmosphere should be harmless. If it is harmful, it must be introduced into the fan inlet pipe through a small pipe. The disadvantage of this method is that a part of the momentum obtained through the impeller will be released for nothing, thus reducing the overall efficiency of the fan. However, because of its simple and convenient method, it is widely used in fan regulation.

　　4. two valve operation method.

　　Two valves are set on the exhaust pipe of the fan, and the volume between the two valves is fixed to a certain value. The volume between the two valves is equivalent to an air tank. The * valve is directly installed near the fan outlet, which is equivalent to a throttle valve. A little throttling can prevent surge; The second valve acts only as a resistance. Practice has proved that this device can not only achieve the stable operation of the system, but also be very beneficial to reducing noise.

　　5. anti surge ring.

　　At present, it has become a general trend to add anti vibration ring to the main air duct in the fan equipment for subway or tunnel. This kind of guide vane can flow back to the blade in reverse direction along the guide vane instead of generating unstable airflow mass through the blade passage when the airflow is rotated and separated. The disadvantage is that in this case, part of the air flow has done useless work, but it can expand the stable working condition range of the fan and narrow the surge area!

　　Surge refers to periodic air outlet and backflow of the fan. Relatively speaking, axial flow fans are more prone to surge, and serious surge will lead to fatigue damage of fan blades.

　　Surge of fan:

　　(1) The fan has abnormal sound, high noise and vibration, the casing temperature rises, and the surge of induced draft fan and forced draft fan makes the furnace negative pressure fluctuate and combustion unstable.

　　(2) The current decreases and swings frequently, and the outlet wind pressure drops and swings.

　　Common causes:

　　(1) When the two fans operate in parallel, the guide vane opening deviation is too large, which means that the fan with small opening falls into the surge zone for operation.

　　(2) The system resistance is too large due to dust accumulation in the flue and air duct or insufficient opening of the flue and air duct baffle.

　　(3) The fan operates at low load for a long time. Treatment principle: generally, the load of the fans for load adjustment and parallel operation shall be similar, and then the possible causes mentioned above shall be found out, and then the corresponding treatment shall be carried out.