Simulation On Characteristics And Flow Field Of Large Flow Hydraulic Pilot-Check Valve

With the development of fully mechanized mining face develops to the direction of large mining height,the support height of hydraulic support is higher and the requirement of its dynamic characteristics is higher also.The hydraulic pilot-check valve plays an important role in the supportting performa-nce.In unloading process of the LEG,the hydraulic pilot-check valve often appears hydraulic shock and vibration,resulting in hydraulic components damaged,eventhough safety accidents.At present,the majority of large hydraulic pilot-check valve's flow rate is 480L/min,the dynamic performance of the support will be affected because of the hydraulic pilot-check valve's limited flow capacity with the emergence of 7m large mining height support.Theref-ore,it is necessary to use a large flow hydraulic pilot-check valve on the large height support.In this paper,the dynamic characteristic and flow field of a pilot-check valve with nominal flow rate of 1000L/min is carried out.The power bond graph model is established from the angle of power flow while the reverse opening of the hydraulic pilot-check small valve spool and large valve spool with small valve spool.According to the power bond graph,the corresponding state space equation is derived,and the nonlinear factors such as the hydrodynamic force and the valve orifice flow are taken into account in the process of building the mathematical model of the system.Then,according to the initial parameters of the system,the mathematical model is simulated and calculated on the Matlab software.It is found that the pressure vibration and shock of the small valve spool is about 0.3s during the small valve spool reverseopening.Large and small valve spool occurs slight vibration while they reverse opening,at this time small spool flow rate relative to large spool flow is very small,indicating that the hydraulic pilot-check valve works from a small flow for pressure relief and large flow for unloading.According to the requirements of the national standard on the shock test of the hydraulic pilot-check valve,the simulation model of the system is built on the simulation software AMESIM.After the initial parameters are set up,the displacement of the valve spool,the flow rate of the valve orifice and the pressure of the return port are analyzed.Through the analysis,it is found that the pressure drop is about 55 MPa in the beginning of the LEG retracting column,which is lower than the national standard requirements for pressure shock.The vibration of the hydraulic pilot-check valve is divided by two steps,the first vibration from the small valve spool and the second from large and small valve spool when they reverse opening.Flow rate of the hydraulic pilot-check valve is about 1200L/min while the valve reverse opening stably.Through force analysis in the process of valve reverse opening,it's found that the main reason of small valve spool vibration for high pressure emulsion effect of rod chamber causes the control rod displacement fluctuation,and the reason of large and small valve spool vibration for hydraulic pressure and steady flow force.Based on the analysis of the vibration mechanism of valve spool,the measures to relief the vibration and shock are put forward.Simulation software ANSYS/FLUENT was used to analyze the 2D and 3D flow field of the hydraulic pilot-check valve,the static pressure nephogram diagr-am and velocity nephogram diagram are obtained.Through the analysis,it is found that the hydraulic pilot-check valve is easy to cause the valve sleeve and spool radial pressure distribution maldistribution because of single reverse inlet,which easily result in valve sleeve and spool stuck.Unreasonable valve sleeve on the damping hole structure causes emulsion flow into the chamber which isformed by valve sleeve and valve body at the beginning of the hydraulic pilot-check valve reverse openning,the influence will extends the opening time of small valve spool and reduces the sensitivity of the hydraulic pilot-check valve.Through the analysis of the dynamic characteristics and flow field of the hydraulic pilot-check valve,the paper preliminary analyzes the possible problems while the valve working and puts forward the optimization schemes,which can provide basises for next designing and optimum.