Configuration of high vacuum unit

Different vacuum systems require different degrees of vacuum. Therefore, it is often necessary to complete by a set of vacuum units, that is, the vacuum pumps working in different pressure ranges are connected in series.

The vacuum pump with high vacuum discharge can meet the requirements of vacuum pump on one side. Obviously, the simplest vacuum unit is a vacuum pump with direct discharge to the atmosphere. However, the high vacuum system generally needs three-stage units, and the medium vacuum system generally needs two-stage units.

It is difficult for a high vacuum pump and a low vacuum pump to form an effective high vacuum unit. There are several reasons for this. The continuity of traffic is one of them. High vacuum pump has the limitation of pressure resistance of the front stage, that is, if the former stage is higher than a certain pressure, the pump can not work normally. When the current stage pump reaches this critical pressure, the pumping speed will be reduced, so the exhaust flow of the front stage pump may be less than that of the main pump. The inconsistency of the flow rate destroys the requirement of flow continuity, which will inevitably cause the vacuum unit not to work normally. However, if a medium vacuum pump is connected between the high and low vacuum pumps, it can serve as a connecting link between the preceding and the following. The flow rate is continuous, and all pumps can work in the best state. Roots pump can work in the medium vacuum range, is the most suitable, so it is also known as roots booster pump, because its compression ratio is not high, just can connect a few PA to hundreds of PA range. When the three-stage high vacuum unit enters a higher vacuum degree, due to the obvious reduction of the exhaust flow of the main pump, the continuity of air extraction can be maintained only by a small front stage pump. In practical application, this method is often used, which can reduce the energy consumption of the unit.

Another reason why high vacuum units often need three-stage units is due to the limitation of suction pressure of high vacuum pump. All pumps have initial working pressure, and traditional high vacuum pumps are in the range of several PA. Therefore, the front stage pump must be pre pumped to this pressure before the main pump can start to work. However, it usually takes a long time for the front-stage pump to pump to this pressure, because the pumping speed of the pump decreases with the decrease of the pressure. Especially for the vacuum unit with periodic air pumping, the time required for reaching the working vacuum degree is required. The longer the pre pumping time is, the longer the time for entering the working vacuum degree is. Therefore, a medium vacuum pump is added to cooperate with the front stage low vacuum pump to realize the working vacuum degree It takes a short time to reach the working pressure of the main pump, so that the system can enter into the working pressure as soon as possible, thus ensuring the use efficiency of the equipment.

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