There are differences in the performance of various vacuum pumps, in addition to meeting the commonality of vacuuming containers. Therefore, it is very important to clarify the tasks that the pump undertakes in the vacuum system when selecting. The functions of the pump in various work fields are mainly summarized as follows.
1. The main pump in the system The so-called main pump is a vacuum pump that directly vacuums the vacuum system to obtain the vacuum required to meet the process requirements.
2. Rough pump The rough pump refers to a vacuum pump that starts to reduce the pressure of the vacuum system from atmospheric pressure and can start working in another pumping system.
3. Foreline pump The foreline pump is a vacuum pump used to maintain the pressure of the front stage of another pump below its pre-stage pressure.
4. Maintaining the pump to maintain the pump means that the evacuation of the air system is very small, and the main foreline pump cannot be effectively utilized. To this end, an auxiliary fore pump with a lower pumping speed is additionally provided in the vacuum system to maintain the normal operation of the main pump or to maintain the low pressure vacuum pump required for the evacuated container.
5. Rough vacuum pump or low vacuum pump The rough and low vacuum pump refers to a vacuum pump that starts from the atmosphere and reduces the pressure of the pumped container to work in the low vacuum or rough vacuum pressure range.
6. High Vacuum Pump High vacuum pump refers to a vacuum pump that operates in a high vacuum range.
7. Ultra-high vacuum pump Ultra-high vacuum pump refers to the vacuum pump working in the ultra-high vacuum range.
8. Booster pump The booster pump is usually referred to as a vacuum pump that operates between a low vacuum pump and a high vacuum pump to improve the pumping capacity of the pumping system in the intermediate pressure range or to reduce the pumping rate of the foreline pump.
When choosing a vacuum pump, you need to pay attention to the following items:
1. The working pressure of the vacuum pump should meet the ultimate vacuum and working pressure requirements of the vacuum equipment. For example, the vacuum coating requires a vacuum of 1×10-5 mmHg, and the vacuum of the vacuum pump selected must be at least 5×10-6 mmHg. The vacuum of the pump is usually chosen to be higher than the vacuum of the vacuum device by half to an order of magnitude.
2. Correctly select the working point of the vacuum pump. Each pump has a certain working pressure range, such as: diffusion pump is 10-3~10-7mmHg. In such a wide pressure range, the pumping speed of the pump varies with pressure, and its stable working pressure range is 5×10. -4~5×10-6mmHg. Therefore, the working point of the pump should be selected within this range, and it should not be allowed to work for a long time at 10-8mmHg. Another example is that the titanium sublimation pump can work at 10-2mmHg, but its working pressure should be less than 1×10-5mmHg.
3. Under the working pressure, the vacuum pump should be able to remove all the gas generated during the vacuum equipment process.
4. Combine the vacuum pump correctly. Since the vacuum pump has selective pumping, sometimes a pump cannot meet the pumping requirements, and several pumps need to be combined to complement each other to meet the pumping requirements. For example, a titanium sublimation pump has a high pumping speed for hydrogen, but it cannot be pumped, and a three-pole sputter ion pump (or a two-pole asymmetric cathode sputtering ion pump) has a certain pumping speed for argon. When combined, the vacuum device will have a better vacuum. In addition, some vacuum pumps can't work under atmospheric pressure, and need pre-vacuum; some vacuum pump outlet pressure is lower than atmospheric pressure, and the foreline pump is needed, so it is necessary to combine the pumps.
5. Requirements for oil pollution from vacuum equipment. If the equipment is strictly required to be oil-free, you should choose various oil-free pumps, such as: water ring pump, molecular sieve adsorption pump, sputter ion pump, cryopump, etc. If the requirements are not strict, you can choose to have an oil pump, plus some oil pollution measures, such as adding cold traps, baffles, oil traps, etc., can also achieve clean vacuum requirements.
6. Understand the composition of the gas to be pumped. The gas contains no condensable vapor, no particle dust, and no corrosiveness. When selecting a vacuum pump, you need to know the gas composition and select the appropriate pump for the pumped gas. If the gas contains vapors, particles, and corrosive gases, consider installing auxiliary equipment such as condensers and precipitators on the inlet piping of the pump.
7. How does the oil vapor from the vacuum pump affect the environment? If the environment does not allow for pollution, you can choose an oil-free vacuum pump or discharge the oil vapor to the outside.
8. The vibration generated when the vacuum pump works has no effect on the process and environment. If the process does not agree, choose a vibration-free pump or take anti-vibration measures.
9. The price, operation and maintenance cost of the vacuum pump.
Selection of water ring vacuum pump 1. Determination of pump type The type of pump is mainly determined by the amount of gas, vacuum or exhaust pressure required for the work.
When working on a pump, you need to pay attention to the following two aspects:
1. As far as possible, it is required to operate in the high efficiency zone, that is, in the region of critical vacuum or critical exhaust pressure.
2. It should be avoided to operate around the large vacuum of zui or the large exhaust pressure of zui. Operating in this area is not only extremely inefficient, but also unstable and prone to vibration and noise. For vacuum pumps with a high degree of vacuum, cavitation often occurs in this area, and the obvious sign of this phenomenon is noise and vibration in the pump. Cavitation can cause damage to parts such as the pump body and impeller, so that the pump cannot work.
According to the above principle, when the vacuum or gas pressure required by the pump is not high, it can be selected firstly in the single-stage pump. If the degree of vacuum or exhaust pressure is high, the single-stage pump is often unable to meet, or the pump is required to have a large volume at a higher vacuum, that is, the performance curve is required to be flat at a higher vacuum, and two can be used. Stage pump. If the vacuum is required to be above -710mmHg, an optional water ring-atmosphere pump or water ring-Roots vacuum unit can be used as the vacuuming device.
If it is only used as a vacuum pump, it is better to use a single-acting pump. Due to the simple construction of the single-acting pump, it is easy to manufacture and maintain, and it is resistant to cavitation under high vacuum conditions.
If only a large volume compressor is used, it is more suitable to use a double-acting pump. Due to the large volume, small volume and light weight of the double-acting pump, the radial force can be automatically balanced, the shaft does not easily produce fatigue fracture, and the service life of the pump is long.
Second, according to the amount of gas required by the system, after the vacuum pump is initially selected, the type of pump is selected. For the vacuum pump, the model of the pump should be selected according to the amount of gas required by the system.
1. The main pump in the system The so-called main pump is a vacuum pump that directly vacuums the vacuum system to obtain the vacuum required to meet the process requirements.
2. Rough pump The rough pump refers to a vacuum pump that starts to reduce the pressure of the vacuum system from atmospheric pressure and can start working in another pumping system.
3. Foreline pump The foreline pump is a vacuum pump used to maintain the pressure of the front stage of another pump below its pre-stage pressure.
4. Maintaining the pump to maintain the pump means that the evacuation of the air system is very small, and the main foreline pump cannot be effectively utilized. To this end, an auxiliary fore pump with a lower pumping speed is additionally provided in the vacuum system to maintain the normal operation of the main pump or to maintain the low pressure vacuum pump required for the evacuated container.
5. Rough vacuum pump or low vacuum pump The rough and low vacuum pump refers to a vacuum pump that starts from the atmosphere and reduces the pressure of the pumped container to work in the low vacuum or rough vacuum pressure range.
6. High Vacuum Pump High vacuum pump refers to a vacuum pump that operates in a high vacuum range.
7. Ultra-high vacuum pump Ultra-high vacuum pump refers to the vacuum pump working in the ultra-high vacuum range.
8. Booster pump The booster pump is usually referred to as a vacuum pump that operates between a low vacuum pump and a high vacuum pump to improve the pumping capacity of the pumping system in the intermediate pressure range or to reduce the pumping rate of the foreline pump.
When choosing a vacuum pump, you need to pay attention to the following items:
1. The working pressure of the vacuum pump should meet the ultimate vacuum and working pressure requirements of the vacuum equipment. For example, the vacuum coating requires a vacuum of 1×10-5 mmHg, and the vacuum of the vacuum pump selected must be at least 5×10-6 mmHg. The vacuum of the pump is usually chosen to be higher than the vacuum of the vacuum device by half to an order of magnitude.
2. Correctly select the working point of the vacuum pump. Each pump has a certain working pressure range, such as: diffusion pump is 10-3~10-7mmHg. In such a wide pressure range, the pumping speed of the pump varies with pressure, and its stable working pressure range is 5×10. -4~5×10-6mmHg. Therefore, the working point of the pump should be selected within this range, and it should not be allowed to work for a long time at 10-8mmHg. Another example is that the titanium sublimation pump can work at 10-2mmHg, but its working pressure should be less than 1×10-5mmHg.
3. Under the working pressure, the vacuum pump should be able to remove all the gas generated during the vacuum equipment process.
4. Combine the vacuum pump correctly. Since the vacuum pump has selective pumping, sometimes a pump cannot meet the pumping requirements, and several pumps need to be combined to complement each other to meet the pumping requirements. For example, a titanium sublimation pump has a high pumping speed for hydrogen, but it cannot be pumped, and a three-pole sputter ion pump (or a two-pole asymmetric cathode sputtering ion pump) has a certain pumping speed for argon. When combined, the vacuum device will have a better vacuum. In addition, some vacuum pumps can't work under atmospheric pressure, and need pre-vacuum; some vacuum pump outlet pressure is lower than atmospheric pressure, and the foreline pump is needed, so it is necessary to combine the pumps.
5. Requirements for oil pollution from vacuum equipment. If the equipment is strictly required to be oil-free, you should choose various oil-free pumps, such as: water ring pump, molecular sieve adsorption pump, sputter ion pump, cryopump, etc. If the requirements are not strict, you can choose to have an oil pump, plus some oil pollution measures, such as adding cold traps, baffles, oil traps, etc., can also achieve clean vacuum requirements.
6. Understand the composition of the gas to be pumped. The gas contains no condensable vapor, no particle dust, and no corrosiveness. When selecting a vacuum pump, you need to know the gas composition and select the appropriate pump for the pumped gas. If the gas contains vapors, particles, and corrosive gases, consider installing auxiliary equipment such as condensers and precipitators on the inlet piping of the pump.
7. How does the oil vapor from the vacuum pump affect the environment? If the environment does not allow for pollution, you can choose an oil-free vacuum pump or discharge the oil vapor to the outside.
8. The vibration generated when the vacuum pump works has no effect on the process and environment. If the process does not agree, choose a vibration-free pump or take anti-vibration measures.
9. The price, operation and maintenance cost of the vacuum pump.
Selection of water ring vacuum pump 1. Determination of pump type The type of pump is mainly determined by the amount of gas, vacuum or exhaust pressure required for the work.
When working on a pump, you need to pay attention to the following two aspects:
1. As far as possible, it is required to operate in the high efficiency zone, that is, in the region of critical vacuum or critical exhaust pressure.
2. It should be avoided to operate around the large vacuum of zui or the large exhaust pressure of zui. Operating in this area is not only extremely inefficient, but also unstable and prone to vibration and noise. For vacuum pumps with a high degree of vacuum, cavitation often occurs in this area, and the obvious sign of this phenomenon is noise and vibration in the pump. Cavitation can cause damage to parts such as the pump body and impeller, so that the pump cannot work.
According to the above principle, when the vacuum or gas pressure required by the pump is not high, it can be selected firstly in the single-stage pump. If the degree of vacuum or exhaust pressure is high, the single-stage pump is often unable to meet, or the pump is required to have a large volume at a higher vacuum, that is, the performance curve is required to be flat at a higher vacuum, and two can be used. Stage pump. If the vacuum is required to be above -710mmHg, an optional water ring-atmosphere pump or water ring-Roots vacuum unit can be used as the vacuuming device.
If it is only used as a vacuum pump, it is better to use a single-acting pump. Due to the simple construction of the single-acting pump, it is easy to manufacture and maintain, and it is resistant to cavitation under high vacuum conditions.
If only a large volume compressor is used, it is more suitable to use a double-acting pump. Due to the large volume, small volume and light weight of the double-acting pump, the radial force can be automatically balanced, the shaft does not easily produce fatigue fracture, and the service life of the pump is long.
Second, according to the amount of gas required by the system, after the vacuum pump is initially selected, the type of pump is selected. For the vacuum pump, the model of the pump should be selected according to the amount of gas required by the system.
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