Vacuum Pump- Vacuum System
Different vacuum systems require different degrees of vacuum. Therefore, it must be completed by a set of vacuum units, that is, vacuum pumps working in different pressure ranges are connected in series.
The vacuum pump on the high vacuum side can reach the vacuum degree required by the system, while the vacuum pump on the low vacuum side is directly exhausted to the atmosphere. Obviously the simplest vacuum system is with a vacuum pump that exhausts directly to the atmosphere. However, high vacuum systems generally require three-stage units, and medium-vacuum systems generally require two-stage units.
It is difficult to form an effective high vacuum system with a high vacuum pump and a low vacuum pump. There are several reasons for this. Continuity of flow is one of them. The high vacuum pump has the limitation of the pressure resistance of the backing pump, that is, the pressure of the backing pump is higher than a certain pressure, and the pump cannot work normally. When the backing pump reaches this critical pressure, the pumping speed is often reduced, so the exhaust flow of the backing pump may be less than the exhaust flow of the main suction pump. It will cause the vacuum system to not work properly. However, if a medium vacuum pump is connected between the high and low vacuum pumps, it can play the role of linking, the flow is continuous, and each pump can work in the best state.
Roots pump can work in the medium vacuum range, which is most suitable, so it is also called the roots booster pump. Because its compression ratio is not high, it can be connected to the range of several Pa to several hundred Pa. When the three-stage high vacuum system enters a higher degree of vacuum, since the exhaust flow of the main suction pump is significantly reduced, only a smaller backing pump can maintain the continuity of the pumping. This method is often used, which can reduce the energy consumption of the vacuum system.
Another reason why high vacuum system often require three-stage units is due to the limitation of the suction pressure of the high vacuum pump. Pump has an initial working pressure, and the traditional high vacuum pump is in the range of several Pa. Therefore, the backing pump must be pre-pumped to this pressure before the main suction pump can start to work. However, it often takes a long time for the backing pump to reach this pressure, because the pumping speed of the pump decreases as the pressure decreases. The time is required. The longer the pre-pumping time, the longer the time to enter the working vacuum. Therefore, adding a medium vacuum pump to cooperate with the backing low vacuum pump can reach the working pressure of the main suction pump in a short time. Make the system enter the working pressure as soon as possible to ensure the use efficiency of the equipment.
Both the roots pump and the oil booster pump can be used as a medium vacuum pump. The molecular booster pump has a very high compression ratio, which not only enables it to obtain a clean vacuum, but also has excellent high vacuum performance and pumping capacity. This makes the molecular booster pump the only vacuum pump with both medium and high vacuum performance at present, so it only needs to cooperate with the low vacuum pump to form a high vacuum system with performance comparable to the three-stage unit.
Specifically, due to the high pressure resistance of the molecular booster pump, the backing pump can be easily in a high flow state, and the molecular booster pump has a high suction pressure, which reduces the pre-pumping burden of the backing pump. The molecular booster pump can work at 100-50Pa, and the pressure of the backing pump from the atmosphere to this pressure basically follows the law that the pressure decreases by an order of magnitude with each elapsed time. Therefore, the vacuum system can have a high pumping efficiency.
Simplifying the high vacuum system and canceling the roots pump is another advantage of the molecular booster pump. For larger high-vacuum application equipment, the pre-pumping capacity of the backing pump can also be appropriately strengthened to further shorten the pumping time. Since the pre-pumping time is very short compared with the entire exhausting process, the use time of the backing pump is also very short, so it can be used as a backing pump for multiple sets, which is often very realistic. This greatly simplifies the vacuum system for large-scale applications.
In some medium vacuum applications, it is necessary to enter the range of 10-1Pa, which is often difficult to achieve for the secondary unit of the roots pump, and the use of the tertiary system connected in series with the secondary roots pump can increase the vacuum degree by an order of magnitude and enter the 10-1Pa, so the three-stage system is also commonly used in medium vacuum applications. Since the molecular booster pump can have a full pumping speed at 10-1Pa, it can also replace the two-stage roots pump in the three-stage medium vacuum system. Generally speaking, the roots pump that works in the low-end pressure range of medium vacuum for a long time can be completely replaced by the molecular booster pump. There should be relatively few roots pumps that work in the high-end pressure range of medium vacuum for a long time, because the backing pump in this pressure range often has a strong pumping speed.
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