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The main factors affecting the performance of the Roots pump

1. The key part of the Roots pump is the rotor, and the key of the rotor is its profile. The outer surface line of the rotor cross section is the profile line of the rotor. When the pump is working, there is no contact between the surfaces of the rotors, but the gap between the rotors must be maintained, so the profile of the rotor must be made into a conjugate curve. When choosing a rotor profile in a practical plan, in addition to meeting the above requirements, the following conditions should also be considered:

(1) The volume application coefficient of the pump rotor should be as large as possible, that is, the volume occupied by the rotor should be small
(2) The rotor should have a good degree of symmetry to ensure stable operation and good exchangeability
(3) Ensure that the rotor has sufficient strength
(4) The rotor should be easy to process, and it is easy to lose high precision

The commonly used rotor profiles include arc tooth shape, involute tooth shape and cycloid tooth shape. Compared with the "arc → involute → cycloid" rotor profile proposed by Southwest University in recent years, the air resistance is larger, which improves the performance of the pump under high pressure, improves the pumping efficiency of the pump, and is more widely used. It is believed that newer and better Roots pump rotor profiles will be presented in the future, which will further improve the working performance of Roots pump.

2. In order to control the gap between the pump rotor, the rotor and the pump casing, the axial and radial displacements of the bearing are required to be controlled within a certain range. When planning, the bearing accuracy should be selected accurately, and the bearing type suitable for the working conditions of the pump should be selected. Considering the effect of axial heat shrinkage of the rotor, the rotor shaft should have a live end (usually a gear end) to allow the shaft to move axially due to factors such as heat shrinkage. The axial gap between the shaft and the rotor and the side end face can be selected to be larger; while the axial gap between the shaft and the rotor and the end cover should be selected to be smaller.

3. It is required that the gear has strong wear resistance, stable transmission, and the gap between the teeth should not be too large. The precision of the gear is usually 5 to 6 grades. In order to make the transmission stable and the noise is small, helical gears are often used. In order to make the gap between the gear device and the adjustment rotor convenient, the gap adjustment gear can be selected and the connection method of the box expansion sleeve is adopted between the gear and the shaft.

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