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Roots pump working principle

Roots vacuum pump is a rotary volumetric vacuum pump. Its structure is evolved from roots blower. It first appeared in Germany in 1944. It is used as a mechanical booster pump for vacuum melting system with large pumping speed in the pressure range of 10-1000Pa.


The structure of roots pump. In the pump chamber, two "8" shaped rotors are mounted vertically on a pair of parallel axles, and are driven by a pair of gears with a transmission ratio of 1 to rotate in reverse synchronously. Between the rotors, there is a certain gap between the rotor and the inner wall of the pump housing. Roots pump is a kind of vacuum pump without internal compression, usually the compression ratio is very low, so the middle and high vacuum roots pump needs the front pump. Therefore, the limit vacuum of Roots pump depends not only on the pump structure and manufacturing accuracy, but also on the limit vacuum of the front pump.


The working principle of roots pump not only has the working principle of the volume pump, but also has the pumping effect of the molecular pump. Because of the continuous rotation of the rotor, the air is sucked from the inlet of the pump into the space V0 between the lower rotor and the pump shell. After suction, the space V0 is completely closed. As the rotor rotates, the closed V0 space is connected with the exhaust port. Because of the high gas pressure on the exhaust side, a part of the gas backlash occurs, resulting in the sudden increase of gas pressure in the V0 space. As the rotor continues to rotate, the original sealed gas in the V0 space, together with the recoil gas, is discharged out of the pump. At this time, the upper rotor seals the V0 volume gas from the pump inlet. Because of the continuous operation of the pump, the two rotors continuously form a closed space V0 and continuously discharge the gas from the closed space, thus achieving the purpose of pumping.

Roots pump.jpg

ZJ Roots Vacuum Pump


Technical Parameters:

ModelZJ-150ZJ-300ZJ-600ZJ-1200
Pumping speed(L/s)1503006001200
Ultimate pressure (Pa)1stage piston pump as backing pump5×10-2
2 stage piston pump as backing pump1×10-1
Max. allowable diff. pressure(Pa)8×1035×103
Motor rotary speed(RPM)3000
Suitable motor power(kW)2.247.511
Flange sizeInlet(mm)100150200250
outlet(mm)100150200200
Cooling water consumption(L/h)120150
Allowable temperature(℃)100
Vacuum pump oil100#
Weight(without motor)(kg)195250760860


The rotor spindle rotates a total of four V0 volume gases in one week. Therefore, the theoretical pumping speed of the pump is: 

formula.jpg

(5.1) A0 - the effective suction area of the pump chamber mm2


N -- revolution of pump shaft r/min


L -- rotor length mm


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