It is very important to choose the pump speed ratio between roots vacuum pump and front stage pump for the composition of roots screw vacuum unit. Because the compression ratio of Roots vacuum pump is very limited. This compression ratio determines the capacity of the previous stage pump because the compression ratio is inversely proportional to the vacuum pumping speed. The compression ratio is between 2 and 10. In addition, consideration should be given to requiring a pre exit.
Vacuum equipment is used as auxiliary equipment in various mechanical equipment. If the time is much better than the pre pump time in normal operation, you can choose a smaller pre pump (compression ratio can be greater). If the vacuum is more airtight and requires to be pre pumped soon, a larger pre pumping will be used. Sometimes, in order to give full play to the efficiency of the equipment, a larger booster pump is installed in front of the unit, which stops after normal operation, and a smaller booster pump is used to save power.
buy roots screw vacuum unit should be considered before：
When selecting the front stage pump, the requirements of the limit pressure of Roots vacuum unit should also be considered. In general, the mechanical pump with two-stage rotary vane oil seal or two-stage sliding mechanical pump is selected as the front pump for the higher requirement of limit vacuum (maximum pressure of 1 × 10-3 PA ~ 1 × 10-2 PA). The limit vacuum degree is required to be between (1 × 10-2Pa ~ 1 × 10-1pa), single-stage oil seal mechanical pump can be selected as the booster pump, and the limit vacuum degree is required to be between 133-1333pa, reciprocating vacuum pump or liquid ring vacuum pump can be selected as the booster pump.
When reciprocating or liquid ring type crude vacuum pump is selected as roots vacuum pump as the front pump, the pump speed of the front pump is generally 1 / 2-1 / 4 of Roots vacuum pump, which should not be too large, otherwise the compression ratio is too large, resulting in high exhaust temperature of Roots vacuum pump, which can not work normally. It is also necessary to consider whether there is corrosive medium in the pumped gas and whether there is a large or small amount of condensable gas.
If there is corrosive gas, oil sealed mechanical pump cannot be used. Oil seal mechanical pump is not suitable to remove the gas containing a large amount of condensable steam, otherwise the sealing liquid will emulsify rapidly. In order to remove the gas containing a small amount of condensable steam, the oil sealed mechanical pump with gas ballast device should also be selected as the booster pump.
In order to obtain high pumping rate at low inlet pressure (1-100 PA), roots vacuum pump can be used as a three-stage or four stage unit and the front stage pump of another roots vacuum pump. At this time, the pump speed ratio between roots vacuum pumps is generally between 2 and 5.
buy roots screw vacuum unit