It has a large suction speed in a wide pressure range;
Quick start, can work immediately;
Not sensitive to dust and water vapor contained in pumped gas;
The rotor does not need lubrication, and there is no oil in the pump cavity;
Small vibration, good rotor dynamic balance condition and no exhaust valve;
Low driving power and low mechanical friction loss;
Compact structure, small floor space;
Low operation and maintenance cost.
Therefore, Roots pumps are widely used in metallurgy, petrochemical, paper-making, food and electronics industries.
Working principle of Roots pump:
The structure of Roots pump is shown in the figure. In the pump room, two 8-shaped rotors are vertically installed on a pair of parallel shafts, and a pair of gear belts with transmission ratio of 1 move synchronously in opposite directions. There are certain gaps between rotors and between rotors and the inner wall of pump casing, which can realize high-speed operation. Roots pump is a kind of vacuum pump without internal compression, and the compression ratio is usually very low, so the high and medium vacuum pumps need the backing pump. The ultimate vacuum of Roots pump depends not only on the structure and manufacturing accuracy of the pump itself, but also on the ultimate vacuum of the backing pump. Roots pumps can be used in series to improve the ultimate vacuum of pumps.
The working principle of roots pump is similar to that of roots blower. Due to the continuous rotation of the rotor, the pumped gas is sucked into the space v0 between the rotor and the pump housing from the air inlet, and then discharged through the air outlet. Because the v0 space is completely closed after inhalation, the gas in the pump cavity will not compress and expand.
However, when the top of the rotor rotates around the edge of the exhaust port and the v0 space communicates with the exhaust side, due to the high gas pressure on the exhaust side, some gas rushes back to the v0 space, which suddenly increases the gas pressure. When the rotor continues to rotate, gas is exhausted from the pump.
The picture shows the pumping process of roots pump rotor from 0 to 180. At position 0 (A in the figure), the lower rotor seals the v0 volume gas from the pump inlet. When it is turned to the 45 position (B in the figure), the cavity communicates with the exhaust port. Due to the high pressure on the exhaust side, a part of the gas flows back. When rotating to the 90 position (C in the figure), the gas sealed by the lower rotor is discharged out of the pump together with the backwashing gas. At this time, the upper rotor also seals the v0 volume gas from the pump inlet. When the rotor continues to rotate to 135 (D in the figure), the gas sealed by the upper rotor is communicated with the exhaust port, and the above process is repeated. The position of 180 (Figure E) is the same as that of 0. The rotor shaft rotates once * * * to discharge four v0 volumes of gas.