Factors that affect the efficiency of LC Roots pumps and key issues in design

{1} Factors that affect the efficiency of Roots oil pumps Although the performance conditions of Roots oil pumps determine that the equipment has excellent work efficiency, many users have expressed that its work efficiency is not as expected. This is mainly because the device will be affected by some external and internal factors during later use, leading to a decrease in its work efficiency. And generally, external factors are nothing more than operating methods, working environment, etc., so let's talk about the internal factors that affect the device. Come and take a look

1. Working steam and its dryness: Low steam pressure and pressure fluctuations have a significant impact on the ability of vacuum pumps. Therefore, steam pressure should not be lower than the required working pressure, otherwise it will cause the Roots oil pump to fail to operate normally, indirectly leading to a decrease in working efficiency

2. Circulating cooling water: If the cooling water supply is insufficient, the condenser will heat up, the airflow sound will increase, the vacuum degree will rapidly decrease, and even steam will return to the exhaust pipe, which will affect the working efficiency of the equipment

3. System sealing of Roots oil pump: When the Roots oil pump is in a state, the water discharged from the front stage is very little, sometimes even not. Therefore, if a large amount of water is discharged from the front pump, it can be considered that there is a leakage in the system. Once leaked, it will seriously affect the efficiency of the equipment

4. Nozzles: Nozzles are important components that affect the performance of vacuum pumps, but due to their working nature, they can easily cause blockages and affect the efficiency of the equipment

Therefore, when you find that the working efficiency of the Roots oil pump is not satisfactory, you can first investigate whether there are any abnormal conditions in the four parts mentioned above. If there are no problems with the equipment itself, then consider whether external factors have caused the decrease in its working efficiency

{2} Key Issues in Roots Pump Design

1. The key component is the rotor, and the key to the rotor is its profile.

. The outer profile of the rotor cross-section is the profile of the rotor. When the pump is working, the surfaces of the rotors do not come into contact, but the gap between the rotors must be maintained to create a conjugate curve for the rotor profile. When selecting the rotor profile in actual design, in addition to meeting the above motion requirements, the following conditions should also be considered:

(1) The volume utilization 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 good geometric symmetry to ensure smooth operation and good interchangeability

(3) Ensure that the rotor has sufficient strength

(4) The rotor should be easy to machine and achieve high accuracy

The commonly used rotor profiles include arc-shaped teeth, involute teeth, and cycloidal teeth. In recent years, the "arc involute cycloid" rotor profile proposed by Northeastern University has a high air resistance, which changes the performance of pumps under low pressure and improves their pumping efficiency, and has been widely used. I believe that there will be new and good rotor profiles for Roots pumps in the future, which will further improve the working performance of Roots pumps

2. In order to control the clearance between the pump rotor and the pump casing, it is required to control the axial and radial displacement of the bearings within a certain range. When designing, the bearing accuracy should be correctly selected and the bearing model suitable for the pump operating conditions should be selected

Considering the influence of axial thermal expansion of the rotor, the rotor shaft should have a movable end (usually the gear end) to allow axial movement of the shaft due to factors such as thermal expansion. The axial clearance between the rotor at the active end of the shaft and the side face can be selected to be larger; The axial clearance between the rotor at the fixed end of the shaft and the end cover should be selected to be smaller

3. It is required that the gears have strong wear resistance, smooth transmission, and the gap between teeth should not be too large. The accuracy of gears is often selected at levels 5-6. To ensure smooth transmission and low noise, helical gears are commonly used. To facilitate the assembly of gears and the adjustment of clearances between rotors, a clearance adjustment structure gear can be selected and a box expansion sleeve connection method can be adopted between the gear and shaft