The Research For The Discipline During Suctioning Gas Of The Roots Vacuum Pumps

The new standard<Performance Measurement Method of Roots Vacuum Pump>was implemented in January 2017.It has become the first internationally accepted performance testing standard for Roots pumps in China.Therefore,based on the new test standards,systematically combing,analyzing and discussing the pumping law of Roots vacuum pump has become an urgent problem to be solved.There are many factors affecting the pumping performance of Roots vacuum pump,among which the profile design of the rotor is the most critical one.Whether the design of rotor profile is reasonable will directly affect the operation of Roots vacuum pump.Firstly,starting from the meshing principle of a pair of conjugate rotors of Roots vacuum pump,taking the circular head rotor profile of Roots vacuum pump as an example,the derivation process of conjugate meshing curve is demonstrated by using coordinate transformation and envelope conditions,and the expressions of each segment curve in the plane direct coordinate system are given.Then the calculation method of the utilization coefficient of the rotor is given,and the calculation formulas of the theoretical pumping speed and the actual pumping speed are given.How to reflect the pumping performance of Roots vacuum pump by the index of zero flow compression ratio is also discussed.The larger the zero flow compression ratio,the less the leakage reflux of Roots pump;and the smaller the zero flow compression,the greater the leakage reflux of Roots pump.It is concluded that the zero flow compression ratio can be used as an important index to judge the pumping performance of Roots vacuum pump.Because Roots vacuum pump cannot be connect to the air directly,it is necessary to use with a front pump before Roots pump to form a Roots pump unit.The pumping characteristics(such as pumping rate,pumping time,etc.)of Roots pump before normal start-up are also of great significance to the design and use of Roots pump units.Aiming at three common working modes of Roots Pump Unit,the pumping characteristics and rules of Roots Pump Unit are analyzed and discussed in turn.According to the characteristics of Roots vacuum pump which needs to cooperate with the front pump,the working effects of different starting modes in the starting stage of Roots vacuum pump are analyzed.Among them,the straight-through Roots pump unit which is directly connected with the front pump in series has the slowest pumping speed and the longest pumping time for the designated container in its work;the Roots pump unit with bypass pipeline is superior to the straight-through Roots pump unit in the performance of pumping speed and time;and the variable-frequency Roots pump unit has the fastest pumping speed and completes the vacuum pumping time for the designated container.The shortest.Therefore,in the start-up stage,using frequency conversion relay control,with the outlet pressure to adjust the power of the frequency conversion Roots pump unit is more efficient than the other two units.It has great research value and good application prospects in the research and production of Roots pump.In addition to the above factors,Roots vacuum pump in work will generate a lot of heat,and cause the thermal deformation of the rotor and pump chamber,which will lead to the change of pumping performance.Therefore,it is particularly important to study the thermodynamics of the gas in the pump.Based on the theory of gas reflux in Roots vacuum pump,the thermodynamic theory of Roots vacuum pump is further improved and optimized on the basis of previous work.Taking one of the most common Roots vacuum pumps,the double-leaf Roots vacuum pump,as an example,the pumping characteristics and operating rules of the double-leaf Roots vacuum pump are expounded by analyzing the variation of the thermodynamic parameters(such as pressure,volume,temperature,mass and internal energy)of the pumped gas in the four processes of suction,transportation,backlash and exhaust,so as to analyze the pumping characteristics and operating rules of the double-leaf Roots vacuum.The mechanism provides methodology of thermal engineering methodology and can be used as a reference for performance optimization of Roots pumps.