1. Get the required limit vacuum and working vacuum in the pumped device or working chamber. Limit vacuum is the vacuum degree that the device achieves without leakage and discharge, and working vacuum is the vacuum degree that can be maintained when the device is vacuum treated. A large amount of gas is emitted during vacuum treatment, and the working vacuum will be significantly lower than the limit vacuum. Limit vacuum degree and working vacuum degree have their own importance. They affect the quality of devices from different aspects.
2. The time required to obtain a working vacuum. The time depends on the pumping speed of the vacuum system. Increasing pumping speed can shorten this time. Large studios clearly require large pumping speeds. Sometimes the studio is small, but because of the serious leakage, the vacuum system also needs a large pumping speed, otherwise a large amount of leakage will greatly reduce the vacuum, making the system unable to work.
3. Suitable residual gas composition in the extracted device or working room. Practice has proved that it is not enough to simply improve and ensure the limit vacuum and working vacuum, and there should be certain requirements for residual gas composition. For example, in order to maintain the sensitivity reduction within one year life of vacuum camera devices, the oxygen content of residual gases in the devices should not be higher than 10-2 Pa high-voltage vacuum switch tube, and hydrocarbon molecules should not be included. The residual gas composition of the vacuum system, if there is no other gas source in the system, mainly depends on the characteristics of the pump.
4. In addition, the vacuum system must be simple in structure, reliable in performance, convenient in operation and maintenance, and inexpensive in price. To meet these requirements, comprehensive consideration must be given to the selection of pumps, the determination and layout of pipe sizes, and the assembly process. These basic requirements are often interrelated. For example, because the vacuum system always has the phenomenon of micro leakage, the pump with high pumping speed can obtain better working vacuum than the pump with low pumping speed, but the large pump is expensive, consumes more water and electricity, so there is a problem of reasonable selection. Miniature vacuum pumps are suitable for instruments and small vacuum systems. They are low cost, high efficiency and low noise. It is inappropriate for some users to choose industrial vacuum pumps with large flow rate.
5. Automation requirements. With the development of computer technology, the automation requirement of vacuum system for users is also increasing. For the vacuum system, the automatic control mainly regulates the flow rate and vacuum degree of the vacuum pump. Vacuum degree is often controlled by adjusting the flow rate of vacuum pump, installing throttle valve and relief valve. It is better to directly adjust the rotational speed of the vacuum pump to reduce energy loss and generate additional noise by throttling.
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