Study On Failure Mode And Mechanism Of Check Valve In Large Flow And High Pressure Plunger Water Pump

The check valve is the key component that controls the inlet and outlet flow of high-pressure plunger water pumps.With the development of plunger pumps towards pure hydration,high-pressure,and high flow rate,the size and weight of the check valve are becoming larger and larger.As a result,the hysteresis effect of the check valve is amplified,and the impact momentum of the large inertia valve plate increases several times.The instantaneous impact flow rate at the valve port increases,causing cavitation and fluid erosion to intensify.The uneven flow field leads to prominent issues such as valve plate bias load.The above issues have become key factors that restrict the improvement of the service life of the large flow check valve.At present,there is still a lack of systematic research on the failure mode of the check valve,and the failure mechanism of the check valve after high flow rate still needs further exploration.Focusing on the above issues,this thesis takes a large flow high-pressure plunger water pump(40MPa,630L/min)as a breakthrough point,takes a large flow high-pressure plunger pump(40MPa,630L/min)as a breakthrough point,and uses a research method that combines liquid-solid coupling dynamics modeling,transient flow field simulation,three-dimensional morphology measurement experiments,explicit dynamics simulation,and theoretical analysis to analyze the problems of flow loss,sealing surface cavitation,rotational wear,and high-speed tilting impact deformation of the plunger pump that occur in the actual service process of the large flow distribution valve.Thus revealing the three main failure modes and mechanisms of high parameter distribution valves.The main work and research results are as follows:(1)The liquid solid coupling driving characteristics of large inertia flow check valve and the distribution law of pump flow loss.The liquid-solid coupling driving model of the plunger,liquid column,and check valve was established,and the dynamic response characteristics of the check valve and the influence of the valve response on the flow loss distribution of the plunger pump were analyzed.The research showed that the opening and closing process of the check valve has asymmetric characteristics of "fast opening" and "slow closing".When the response frequency of the check valve is too low,it will cause an increase in the instantaneous closing speed and closing hysteresis of the check valve,making it have a "lagging and fast closing" characteristic.At high speeds,the volumetric efficiency loss of the plunger pump is mainly caused by the lag in closing the valve.Increasing the comprehensive response frequency of the plunger valve system is beneficial for improving the volumetric efficiency of the plunger pump.(2)The transient cavitation evolution law and cavitation failure mechanism of the check valve.The transient flow field simulation results of the entire process of opening and closing indicate that the valve has gone through three stages: opening cavitation,throttling cavitation,and jet cavitation.Among them,the duration of throttling cavitation is the longest,and the intensity of jet cavitation is the highest.Increasing the spring stiffness and preload,or reducing the mechanical limit of the valve plate,is beneficial for reducing the strength of jet cavitation.However,if the mechanical limit is too low,it will exacerbate throttling cavitation,and increasing the valve chamber diameter is beneficial for reducing the risk of throttling cavitation.Moreover,the farther the initial position of the plunger is from the axis of the suction valve,the shorter the duration of low pressure inside the valve.The higher the amplitude of inlet pressure pulsation,and the longer the total cavitation duration.Cavitation inside the valve leads to continuous corrosion pits in the area where steam accumulates on the sealing surface of the valve seat.The more the number and radius of corrosion pits,the more significant the stress concentration phenomenon on the sealing surface.Under the action of high-frequency cyclic alternating loads,the edges of corrosion pits are prone to fatigue failure,leading to fatigue failure of the sealing surface.(3)The rotating motion law and wear failure mechanism of the valve.The rotational motion characteristics of the valve in high-speed asymmetric flow field and the failure mechanism of different materials’ rotational wear have been studied through numerical simulation,visualization experiments of valve plate rotation,and microscopic measurement experiments of wear morphology.The results indicate that the valve plate has a rotational speed of 0.0306rad/s at the moment of closure,resulting in relative slip between the valve plate and the valve seat during dynamic contact,and generating cutting wear marks on the sealing surface.Under the combined action of low-speed rotating cutting and high-frequency high-speed impact of the valve plate and valve seat,the sealing surface undergoes rotational wear and material loss.The use of materials with high surface hardness is beneficial for improving the impact resistance and wear resistance of the valve plate.(4)The high-speed asymmetric motion law and tilting impact failure mechanism of the check valve.The transient flow field simulation results show that the valve plate tilts under the action of radial unbalanced torque in the high-speed asymmetric flow field,and the maximum tilt angle of the valve plate during a single opening and closing process can reach 0.05044rad(2.89 °).At the moment of oblique impact,local high stress is generated on the outer circle of the valve core and the sealing surface of the valve seat.The damage morphology of the distribution valve is mainly caused by wear on the edge of the valve core and local concave deformation of the valve seat,with maximum deformation depths of 1.48 mm and 2.504 mm,respectively.As the impact angle and impact speed increase,the peak value of local stress gradually increases.When the valve plate impacts the valve seat at a collision speed of 0.98m/s and a 3°inclination angle,the maximum local equivalent stresses on the outer circle of the valve plate and the sealing surface of the valve seat are 440.61 MPa and 197.22 MPa,respectively.Under the impact of the valve plate on the valve seat at 7-8 times per second,the sealing surface undergoes cyclic stress and high cycle fatigue failure.