The Principle of Roots Pump

In the pump chamber, there are two "8" shaped rotor perpendicular to each other mounted on a pair of parallel shafts, by the gear ratio of

1 of a pair of gear belt action with each other to reverse the synchronous rotary movement. Between the rotors, between the rotors and the inner wall of the pump casing, a certain clearance is maintained.

There is a certain clearance between the rotors and the inner wall of the pump casing, so that high speed operation can be realized. As the Roots pump is a vacuum pump without internal compression, the compression ratio is usually very low.

is very low, so high and medium vacuum pumps need a pre-stage pump. The ultimate vacuum of the Roots pump depends on the structure of the pump itself and the manufacturing accuracy, but also on the ultimate vacuum of the preceding pump.

It also depends on the ultimate vacuum of the pre-stage pump. In order to increase the ultimate vacuum of the pump, the Roots pump can be used in series.

The working principle of the Roots pump is similar to that of the Roots blower. Due to the continuous rotation of the rotor, the pumped gas is sucked in from the inlet port into the space v0 between the rotor and the pump casing, and then discharged through the exhaust port. As the space v0 is completely closed after suction, there is no gas in the pump chamber.

So, there is no compression and expansion of the gas in the pump chamber.

However, when the top of the rotor turns over the edge of the exhaust port and the v0 space is connected with the exhaust side, due to the higher gas pressure on the exhaust side, a part of the gas is flushed back into the space.

Then a part of the gas back to the space v0 to go, so that the gas pressure suddenly increased. When the rotor continues to rotate, the gas is discharged out of the pump.