Study On Internal Flow Field And Speed Limit Of External Involute Spur-gear Pump

External gear pump is widely used in mechanical equipment because of its simple and compact structure,small size,light weight,good self-priming ability,insensitivity to oil pollution and many other advantages.In this paper,an external involute spur-gear pump is taken as the research object.Through theoretical calculation and simulation,the pressure pulsation in the trapped oil area,cavitation characteristics and speed limit of the involute external spur-gear pump are analyzed and studied.The methods for reducing the pressure pulsation in the trapped oil zone,preventing cavitation generation and increasing the rotational speed of the external spur-gear pump are proposed,which lays a foundation for realizing the high speed of the gear pump.Firstly,analyze the structure of the external involute spur-gear pump to get the mechanism of the trapped oil phenomenon.Analyze the development of oil trapped in detail and calculate the rate of change of the trapped oil volume of the gear pump.Simulate and analyze the pressure pulsation in several positions in the gear pump,it is found that the pressure fluctuation in the trapped oil area is the largest.In addition,study the effects of inlet pressure,outlet pressure,oil gas content and unloading groove on the pressure fluctuation of the trapped oil area.Secondly,find out the reason for the cavitation of the external involute spur-gear pump through theoretical analysis,and understand the evolution process of cavitation.Using the Pumplinx software to simulate the internal flow field of the external gear pump model,it is found that the cavitation of the external gear pump mainly occurs in the oil suction area near the gear meshing point.And study the influence of the cavitation at different inlet pressure,outlet pressure,the size of the inlet,the oil gas rate,temperature,speed,viscosity and groove structure.Then propose the methods to prevent cavitation based on the results.Finally,analyze the influence of the limit rotation speed of the external gear pump on the working performance of the pump,and introduce the significance of studying the limit speed.Define the speed limit of the external gear pump and obtain the speed-flow curve by simulation to determine the speed limit in the self-priming.Change the suction pressure,inlet size,viscosity and oil gas content respectively,simulate and obtain the speed limit of the gear pump under different conditions.Analyze the influence of these factors on the speed limit of the gear pump,and put forward some measures to increase the speed of the gear pump.