Vacuum pump unit is composed of roots pump as the main pump and rotary vane pump as the front pump in series. But it doesn't mean that the two pumps can be combined and used casually. Only by meeting certain requirements can the two pumps form a unit. The composition conditions are as follows:
The function of the front stage pump is to reduce the vacuum discharge pressure of roots pump, so as to control the pressure difference and compression ratio between the inlet and exhaust within a certain range. Because the compression ratio of roots pump is limited, it is important to choose pumping speed. The compression ratio of roots pump changes with the change of discharge pressure. At high discharge pressure, the compression ratio is 3:1, and the compression ratio can reach 40:1 or higher between 1 and 10 mbar.
The pumping speed of the front stage pump shall be selected according to the long-term working pressure range of the vacuum pump unit. In addition, we should consider the demand for the length of pre pumping time. If the working time is longer than the pre pumping time, a smaller pre pump can be selected;
If the vacuum chamber is large, and it is required to reach the pre vacuumizing degree soon, a large pre-stage pump shall be used. It should be noted that the actual operation time difference of roots pump shall not exceed its allowable value, and it is generally recommended to control it below 75%, otherwise, the vacuum pump unit will overheat, overload or bite.
The selection of vacuum pump unit needs to be considered from the service conditions of the main pump and auxiliary pump, so that it can not only be used to extract air and other non condensable and non corrosive gases, but also can be used in various vacuum systems requiring large pumping speed and high vacuum.
VACUUM FURNACE
industrial vacuum pumps,vacuum furnaces
Heat treatment equipment
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