Working principle and structural characteristics of roots pump
Date of issue:2021/8/19 15:33:58 Number of Views:
Roots pump is a double rotor positive displacement vacuum pump. There are two symmetrical rotors in the pump cavity, and the rotor shape has two leaves, three leaves and four leaves. The two rotors rotate in opposite directions to each other and rotate synchronously driven by the shaft end gear. The rotors are not in contact with each other, and the rotor is not in contact with the pump cavity wall. There is usually a gap of 0.15 ~ 1.0mm, and the pump cavity is sealed by the gap.
Because there is no friction in the roots pump cavity, the rotor can run at high speed, generally 1500 ~ 3000r / min, and there is no need to use lubricating oil, so the oil-free and clean air extraction process can be realized. The lubrication parts of the pump are limited to bearings, gears and dynamic seals. The pump has no reciprocating parts, so it can achieve good dynamic balance. Therefore, the roots pump has the advantages of stable operation, high speed, small size and large pumping speed.
At present, most Roots pumps at home and abroad are of horizontal structure, with the air inlet at the top and the exhaust outlet at the bottom. This horizontal structure has low center of gravity and good stability during high-speed operation. The two rotors of roots pump rotate synchronously through a pair of high-precision gears.
Most of the pump drives are direct coupled, while large pumps are belt driven. The motor and transmission gear are mostly arranged on both sides of the rotor shaft, which is convenient for installation and disassembly. The torque transmitted by the driving shaft is large, the shaft shall have sufficient strength and stiffness, and the shaft and rotor shall be firmly consolidated. The sealing of roots pump is very important. A dynamic seal is set between the extended part of the driving shaft, the bearings of the two rotors and the pump cavity, and a static seal is set between the pump cavity and each end cover.
In order to avoid misoperation of roots pump, bypass overflow valve is generally set. According to the special needs of roots pump, it is also possible to make the oil gearbox, bearing and other parts into a separate structure with the pump cavity.
The heat generated in the compression process of roots pump is transferred to the rotor and pump body. It is difficult for the rotor to transfer heat outside the pump, and the heat of the pump body is easy to be lost to the surrounding atmosphere. Therefore, there is a temperature difference between the rotor and the pump body. It intensifies the thermal expansion of the rotor. When the pump load increases, the rotor expansion will disappear the clearance and be stuck. Therefore, there is an air-cooled Roots pump, which uses the cooled gas or atmosphere to directly cool the hot rotor, so as to reduce the temperature difference between the rotor and the pump shell and improve the heat resistance of roots pump.
The air-cooled Roots pump can work under the condition of high pressure difference and high compression ratio. The pump has simple structure, and the cooler is connected with the outlet of the pump, which is convenient for maintenance and replacement. Due to uniform heat dissipation, the gap between the rotor and the pump body can still be kept very small, which is conducive to the improvement of pump volumetric efficiency.
Roots pump is a double rotor positive displacement vacuum pump. There are two symmetrical rotors in the pump cavity, and the rotor shape has two leaves, three leaves and four leaves. The two rotors rotate in opposite directions to each other and rotate synchronously driven by the shaft end gear. The rotors are not in contact with each other, and the rotor is not in contact with the pump cavity wall. There is usually a gap of 0.15 ~ 1.0mm, and the pump cavity is sealed by the gap.
Because there is no friction in the roots pump cavity, the rotor can run at high speed, generally 1500 ~ 3000r / min, and there is no need to use lubricating oil, so the oil-free and clean air extraction process can be realized. The lubrication parts of the pump are limited to bearings, gears and dynamic seals. The pump has no reciprocating parts, so it can achieve good dynamic balance. Therefore, the roots pump has the advantages of stable operation, high speed, small size and large pumping speed.
At present, most Roots pumps at home and abroad are of horizontal structure, with the air inlet at the top and the exhaust outlet at the bottom. This horizontal structure has low center of gravity and good stability during high-speed operation. The two rotors of roots pump rotate synchronously through a pair of high-precision gears.
Most of the pump drives are direct coupled, while large pumps are belt driven. The motor and transmission gear are mostly arranged on both sides of the rotor shaft, which is convenient for installation and disassembly. The torque transmitted by the driving shaft is large, the shaft shall have sufficient strength and stiffness, and the shaft and rotor shall be firmly consolidated. The sealing of roots pump is very important. A dynamic seal is set between the extended part of the driving shaft, the bearings of the two rotors and the pump cavity, and a static seal is set between the pump cavity and each end cover.
In order to avoid misoperation of roots pump, bypass overflow valve is generally set. According to the special needs of roots pump, it is also possible to make the oil gearbox, bearing and other parts into a separate structure with the pump cavity.
The heat generated in the compression process of roots pump is transferred to the rotor and pump body. It is difficult for the rotor to transfer heat outside the pump, and the heat of the pump body is easy to be lost to the surrounding atmosphere. Therefore, there is a temperature difference between the rotor and the pump body. It intensifies the thermal expansion of the rotor. When the pump load increases, the rotor expansion will disappear the clearance and be stuck. Therefore, there is an air-cooled Roots pump, which uses the cooled gas or atmosphere to directly cool the hot rotor, so as to reduce the temperature difference between the rotor and the pump shell and improve the heat resistance of roots pump.
The air-cooled Roots pump can work under the condition of high pressure difference and high compression ratio. The pump has simple structure, and the cooler is connected with the outlet of the pump, which is convenient for maintenance and replacement. Due to uniform heat dissipation, the gap between the rotor and the pump body can still be kept very small, which is conducive to the improvement of pump volumetric efficiency.
