Key Points You Need to Understand When Designing a Vacuum System!

A vacuum system refers to a device composed of a vacuum pump, vacuum gauge, and various components connected through pipes in a suitable manner to achieve a certain vacuum level. What are the basic requirements of a vacuum system?

　1. To obtain the required ultimate vacuum and working vacuum level in the pumping device or chamber.

The vacuum level refers to the vacuum achieved by the device when there is no leakage, while the working vacuum level refers to the vacuum that can be maintained during the vacuum processing of the device. During vacuum processing, a large amount of gas is often released, and at this time, the working vacuum level will be significantly lower than the ultimate vacuum level. Both the ultimate vacuum level and the working vacuum level are important, and they affect the quality of the device from different aspects. For example, in the exhaust vacuum system of oxide cathode devices, the electric 10-2 extreme gas removal and cathode decomposition will release a large amount of gas. If the working vacuum level is poor, it may lead to oxidation of the electrode and poor cathode activation. However, when the device is finally sealed, there is basically no leakage, and the vacuum level inside the device depends on the ultimate vacuum level of the exhaust vacuum system.

　2. The time required to achieve a certain working vacuum level.

This depends on the pumping speed of the vacuum system. Increasing the pumping speed can shorten this time. A large chamber obviously requires a large pumping speed. Sometimes, even if the chamber is not large, if there is severe leakage, the vacuum system will also need a large pumping speed; otherwise, a large amount of leakage will significantly reduce the vacuum level, making the system unable to operate.

　3. There should be suitable residual gas components in the pumped device or chamber.

Simply improving and ensuring the ultimate vacuum level and working vacuum level is not enough; there should also be certain requirements for the residual gas components. For example, in vacuum imaging devices, to maintain a sensitivity reduction of no more than 10% within a one-year lifespan, the oxygen content of the residual gas inside the device should not exceed 10-2Pa. In high-pressure resistant vacuum switch tubes, there should be no hydrocarbon molecules, etc. The residual gas components of the vacuum system, if there are no other gas sources in the system, mainly depend on the characteristics of the pump.

4. The vacuum system must also have a simple structure, reliable performance, convenient operation and maintenance, and low cost.

These requirements must be comprehensively considered from various aspects such as pump selection, pipe size determination and layout, and assembly process. The above basic requirements are often interrelated. For example, since there is inevitably some micro-leakage in the vacuum system, using a pump with a large pumping speed can achieve a better working vacuum level than using a pump with a small pumping speed. However, large pumps are expensive, consume more water and electricity, so there is a need for reasonable selection. Instruments and small vacuum systems should use micro vacuum pumps, which are low-cost, efficient, and low-noise. Some users choosing larger industrial vacuum pumps with higher flow rates are not suitable.

　5. Automation requirements.

With the development of computer technology, users' requirements for the automation of vacuum systems are also continuously improving. For vacuum systems, automatic control mainly involves adjusting the flow rate and vacuum level of the vacuum pump. The vacuum level is often controlled by adjusting the flow rate of the vacuum pump, installing throttling valves, and pressure relief valves. Using throttling methods can lead to significant energy loss and additional noise; it is best to directly adjust the speed of the vacuum pump. There are various methods for speed regulation of industrial vacuum pumps, mainly divided into two categories: the first category is where the motor speed remains constant, and the speed of the vacuum pump is changed through additional devices, such as gearbox speed regulation; the second category is directly changing the motor speed, such as using silicon-controlled rectifier series speed regulation, variable frequency speed regulation, etc. Currently, the commonly used method for industrial vacuum pumps is variable frequency speed regulation, which has good energy-saving effects, can achieve stepless speed regulation, has a large speed regulation ratio, precise speed regulation, and stable speed.

For micro vacuum pumps used in small vacuum systems, pressure-reducing speed regulation was mainly used in the past. The benefit of pressure-reducing operation is that it helps extend the life of the pump and motor. However, if the pump load is too large, it can easily cause the motor to fail to start after pressure reduction, leading to an increase in motor temperature and creating safety hazards. Currently, the most advanced domestic "Gas Sea" speed-regulating micro vacuum pump is equipped with imported brushless DC motors, has built-in PWM (Pulse Width Modulation) lines, can conveniently and reliably adjust the flow rate, can output motor speed feedback signals (FG), and can monitor the motor's working condition in real-time, making it easier for automatic control. It also has a complete self-protection function, which can automatically shut down in case of pump jamming, overheating, and other unexpected situations. Speed-regulating micro vacuum pumps are an ideal choice for the automation of small vacuum systems.

For vacuum systems with good airtightness, if there is no frequent venting and no vapor sources inside, a smaller pump with a better ultimate vacuum level can be used. However, if the system has significant leakage, it is necessary to ensure the working vacuum level by increasing the pumping speed, in which case a pump with a larger pumping speed should be used, and the pipeline flow should be maximized, i.e., using short and wide pipes.

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