Conservative high vacuum pumps are within a few Pa range. Therefore, the front pump must be pre-pumped to this pressure before the main pump can start to work. However, it often takes a long time for the fore-stage pump of direct discharge to reach this pressure. Another reason why high vacuum units often need three stage units is due to the limitation of suction pressure of high vacuum pumps. All pumps have initial operating pressure. Because as the pressure to reduce the pumping speed of the pump in reducing, especially for the periodic vacuum suction unit, to meet the requirements of the vacuum degree of work time is the drainage of the longer the time, also the longer period of time in the vacuum degree of work, therefore, increase the taichung with low level before the vacuum pump, vacuum pump can achieve in a relatively short time main pump can work stress, so that we can make the system as soon as possible into the work pressure, guarantee the efficiency of the equipment.
Roots pump and oil booster pump can be used as medium vacuum pump, the molecular booster pump has a very high compression ratio, which in addition to enabling it to obtain a clean vacuum but also has excellent high vacuum performance, while in the vacuum range also has a super pumping capacity. This makes the molecular booster pump into the current both high and medium vacuum performance of the vacuum pump, so only need to cooperate with the low vacuum pump can be composed of a high vacuum unit performance comparable to the three units. Specifically, due to the high pressure of the molecular booster pump, so the front pump can be easy to be in a high flow state; And the molecular booster pump suction pressure, reducing the pre - pumping burden of the pump. The molecular booster pump can work in 100-50pa, the front stage pump from the atmosphere to this pressure, basically follow the law of every time pressure reduction by an order of magnitude, therefore, the unit can have a very high pumping efficiency. Simplifying high vacuum units and eliminating roots pumps is another advantage of molecular booster pumps.
For larger high vacuum application equipment, can also be appropriate to strengthen backing pump drainage ability, further shorten extraction time, due to the drainage time compared with the whole process of exhaust is very short, so the pump before use time is very short, so you can double as many sets of equipment of the drainage effect, and it is often very real vacuum pump oil in the air (oxygen) and the presence of metal catalysts, oxidation time, under a certain temperature can present the changes of acid value, viscosity of oil and generate the status of the sediment. With the application process and the attack of oxidation, so gradually produce some aldehydes, ketones, acids and colloid, asphaltene and other substances, oxidation stability is to inhibit the above conducive to the use of oil substances generated performance. Water vapor in the tightening process will condense into water droplets, and mix with the pump to form a suspension, not only will make the vacuum degree landing, but also can make the pump cavity and rotor rust, damage the sealing surface, the ultimate vacuum degree landing pump. Therefore, it is important to prevent water vapor from contaminating mechanical pumps.
The prevention measures of vacuum unit are as follows:
Oil seal mechanical pump with gas ballast device is selected; Filling oil separator, centrifugal separator or oil and water separator, will be mixed with water to stop the disposal of the mechanical pump oil, the disposed oil into the pump for use; Use single adjustment with strong water absorption; The use of liquid nitrogen cold trap can not only effectively absorb water vapor, but also prevent the mechanical pump oil from flowing back to the high vacuum chamber.
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