The so-called vacuum system, it refers to the vacuum pump, vacuum gauge and various parts through the pipeline in an appropriate way, the combination of a certain vacuum degree requirements. The basic requirements of vacuum system are as follows:
Obtain the required limit vacuum and working vacuum in the device or working chamber. The limiting vacuum degree refers to the vacuum degree achieved by the device without leakage and outgassing. The second working vacuum degree refers to the vacuum degree that can be maintained when the device is vacuum treated. A large amount of gas will be released during vacuum treatment, and the working vacuum will be significantly lower than the limit vacuum degree. The limiting vacuum degree and the working vacuum degree have their own importance, and they affect the device quality from different aspects. For example, in the exhaust vacuum system with oxide cathode devices, a large amount of gas will be discharged from the electrode degassing and cathode decomposition. If the working vacuum is poor, the electrode may be oxidized and the cathode activation is not good. However, when the device is finally sealed off, there is basically no leakage gas. The vacuum degree in the device depends on the limit vacuum degree of the exhaust vacuum system.
The time required to obtain a working vacuum. This time depends on the pumping speed of the vacuum system. Increasing the pumping speed can shorten the time. Large workrooms, such as aerospace simulation devices, obviously need large pumping speed. Sometimes the working room is not big, but because of the serious leakage and deflation, the vacuum system also needs large pumping speed. Otherwise, a large amount of leakage gas will greatly reduce the vacuum degree and make the system unable to work.
There is a suitable residual gas composition in the extracted device or working room. It has been proved by practice that it is not enough to improve and guarantee the limit vacuum degree and working vacuum degree only, and there are certain requirements for the composition of residual gas. For example, in order to keep the sensitivity of the vacuum camera device within one year, the oxygen content of the residual gas in the device should not be higher than 10-2Pa, and the high pressure resistant vacuum switch tube should not contain hydrocarbon molecules.
In addition, the vacuum system must be simple in structure, reliable in performance, convenient in operation and maintenance, and cheap in price. In order to meet these requirements, it is necessary to consider the selection of pump, the determination and layout of pipe size, and assembly process. At the same time, these basic requirements are often interrelated. For example, because there is always micro leakage in the vacuum system, the pump with high pumping speed can obtain better working vacuum than the pump with low pumping speed. However, the price of large pump is expensive, and the water and power consumption are more, so there is a problem of reasonable selection.
Generally speaking, for the vacuum system with good air tightness, if there is no regular exhaust and no steam source inside, the smaller pump with better limit vacuum can be used. However, if there is a lot of leakage gas in the system, it is necessary to increase the pumping speed to ensure the working vacuum. At this time, the pump with higher pumping speed should be used and the pipeline flow conductivity should be increased as much as possible, that is, the short and thick pipeline should be selected.
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