Study On Flow Characteristics Of Large Pilot Valve In Low Pressure Hydraulic Servo System

Hydraulic servo motor has the advantages of high precision adjustment,large output torque,rapid response and stable operation.It is widely used in the actuator of DEH system to regulate the steam turbine.Its performance directly affects the regulation quality of steam turbine.At present,there are some problems in the research of internal flow structure of hydraulic servo motor,such as lack of research data,lack of in-depth research,imperfection and so on,which bring some difficulties to the development of domestic hydraulic servo motor and the improvement of hydraulic servo motor performance.Therefore,it is necessary to study the characteristics of internal valve port of hydraulic servo motor.In this paper,the large diameter pilot valve(located at the lower end of the relay piston)of the low-pressure hydraulic servo motor system is taken as the research object.Aiming at the three types of valve ports: round valve port,stepped round hole valve port and rectangular valve port,the distribution of the internal flow field and the characteristics of the valve port are studied by combining theoretical analysis,flow field simulation and experiment.The main work of this paper is as follows.(1)Based on CFD simulation technology,the velocity distribution and pressure distribution of the internal flow field of the circular valve port,stepped round hole valve port and rectangular valve port are studied,and the influence of different valve port opening and different inlet and outlet pressure difference on the internal flow field distribution is studied.(2)According to the form of throttling window,the flow area calculation formulas of round orifice,stepped round orifice and rectangular orifice are derived,and the flow area characteristics of three types of orifice are analyzed,so as to prepare for the subsequent calculation of the orifice flow coefficient.(3)The flow characteristics of three kinds of valve ports under different valve opening and different inlet and outlet pressure difference are studied.On this basis,combined with the calculation formula of valve port flow area deduced before,the variation law of valve port flow coefficient with valve opening and inlet and outlet pressure difference is analyzed.(4)A test platform was built to test the flow characteristics and flow coefficient of the round and rectangular valve ports.The test results were compared with the simulation results to verify the correctness of the simulation model and the simulation results.Through the above work,we can get the influence law of the large diameter pilot valve opening and the pressure difference between the inlet and outlet on the flow field distribution,flow characteristics and flow coefficient.It provides a technical basis for the development and upgrading of domestic hydraulic motors.