Research On The Elevating Force, Flowrate And Instability Characteristics For The Relief Valve In Rock Drill System

Drill rig is an equipment that drills holes in mine.There widespreadly exist error of pressure adjustment, pressure oscillation, output actions shadow, pressure loss, high noise with respect to relief valve in rock drill system.Instablity behaviors in the process of constant pressure relieving and overpressure protection cause drill arms shakes, low position accuracy and difficult slag discharge. It affects the efficiency of rock drilling.The pressure relief valve is a type of valve used to control or limit the pressure in a system or vessel which can build up for a process upset, instrument or equipment failure. The pressure is relieved by allowing the pressurised fluid to flow from an auxiliary passage out of the system. The relief valve is designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. More and more attention has been paid to the development of continuous operation ability of the drill rig and vibration and noise reduction in rock drill system.In this paper, the research object is the relief valve in rock drill system, and the instability characteristic is the entrance.For the case of compressible flow, a method was presented by considering relief valve as ideal converging-only nozzle.We divided relief valve into three kinds of flows, i.e. subcritical flow, critical flow and supercritical flow.According to the curve of flow ratio and backpressure ratio, a method to predict both subcritical and critical flow conditions is based on the hypothesis that compressibility may be approximated by the geometrical form of a quarter of ellipse.Flux characteristic curve of ellipse formulation was also presented.For the case of incompressible flow, instability phenomenon of cone relief valve was analyzed based on non-smooth bifurcation theory and continuation method.To improve the stability characteristic of relief valve, a nondimensional mathematical model was derived by considering tubes elasticity and energy loss when valve poppet impacts with its seat. Linear stability and Lyapunov exponents analysis were presented.Phase and vector field diagrams were drawn with different nondimensional pre-stress parameters by using softwares XPPAUT and MATLAB. The stable equilibrium states of the system were obtained.One-parameter and two-parameter bifurcation diagrams were drawn. The results showed that there were Hopf bifurcation, saddle-node bifurcation of cycles, generalized Hopf bifurcation and cusp bifurcation in the system. The spool displacement diagram and spectra waterfall diagram were presented. The results showed chaos or impacting period oscillation when low flowrate. Enlarging flowrate could improve the stability characteristic of poppet. The results showed period oscillation without impact or stable equilibrium when large flowrate.For both case of compressible and incompressible flow, the operating principle of relief valve was analyzed. A mathematical model of elevating force was derived. Factors of valve core structures that have effect on the elevating force characteristics were analyzed.This paper introduced the technical parameters that measure flow characteristic of relief valve. Factors of valve lifts that have effect on the flow characteristics were analyzed.Experimental investigation of elevating force characteristics was conducted.The measured elevating forces and pressure differential diagrams were drawn with different valve lifts and flowrates.The theoretical and measured elevating forces were compared and analyzed.The coefficient of local resistance and equivalent area diagrams were drawn with different valve lifts and flowrates.The forms of static and dynamic instability were analyzed. Experimental investigation of instability characteristics was conducted.Factors on different flowrates,set pressures and inlet tube lengths that affect instability characteristics were investigated.Water hammer phenomena on chatter instability were analyzed. The theoretical and measured water hammer pressures were compared and analyzed.Through the theoretical, simulation and empirical research, we provided guides in theory and methods for the stability of relief valve.