Multi stage roots vacuum pump
In Roots vacuum pump, in addition to wet roots pump and air-cooled Roots pump, there are also multi-stage Roots vacuum pump, which can directly discharge the atmosphere without the need for a front-end pump. Because it is rare in daily life, many people don't know about it. Let the oil-free vacuum pump manufacturer take you to have a simple understanding.
Multi stage roots vacuum pump is one of the dry roots vacuum pumps. It is widely used in semiconductor and chemical industry in America, Japan and other countries. Compared with the traditional "single stage" roots vacuum pump with one rotor, its "multi-stage" rotor is in series in form, and the middle wall is isolated to form a number of relatively independent pump cavities. The pump cavities at all levels are connected with the exhaust ports through the air inlet of each stage to form the air flow channel. The diameter and shape of rotors at each stage are the same, but the width may be the same or different. Otherwise, the high pressure side will be narrowed.
The rotor series connection of multi-stage Roots vacuum pump can not improve the pumping speed of the pump itself, and the theoretical pumping speed depends on the pumping speed of the first stage. However, it can achieve a high compression ratio. The pumped gas enters the pump cavity from the first stage air inlet. After compression, it will continue to be compressed until the last stage is discharged to realize multi-stage compression. Therefore, it can realize direct exhaust to the atmosphere without the need for the front stage pump. The multi-stage Roots vacuum pump with 3-6 stages can be pumped to the limit pressure of 1pA from atmospheric pressure.
However, high compression ratio in the multi-stage Roots vacuum pump will also cause overheating and expansion of the rotor. In order to avoid jamming, the rotor will be cooled at the high-pressure end. Generally, through air cooling, the gas flow discharged from the exhaust ports of each stage is cooled by the cooler and then returned to the working chamber of the stage. The cooling gas is used to cool the rotor. This cooling method has to sacrifice the pumping speed.