Effect of Dynamic Pressure Feedback Orifice on Stability of Cartridge-Type Hydraulic Pilot-Operated Relief Valve

Current research on pilot-operated relief valve stability is primarily conducted from the perspective of system dynamics or stability criteria,and most of the existing conclusions focus on the spool shape,damping hole size,and pulsation frequency of the pump.However,the essential factors pertaining to the unstable vibration of relief valves remain ambiguous.In this study,the dynamic behavior of a pilot-operated relief valve is investigated using the frequency-domain method.The result suggests that the dynamic pressure feedback orifice is vital to the dynamic characteristics of the valve.A large orifice has a low flow resistance.In this case,the fluid in the main spring chamber flows freely,which is not conducive to the stability of the relief valve.However,a small orifice may create significant flow resistance,thus restricting fluid flow.In this case,the oil inside the main valve spring chamber is equivalent to a high-stiffness liquid spring.The main mass-spring vibration system has a natural frequency that differs significantly from the operating frequency of the relief valve,which is conducive to the stability of the relief valve.Good agreement is obtained between the theoretical analysis and experiments.The results indicate that designing a dynamic pressure feedback orifice of an appropriate size is beneficial to improving the stability of hydraulic pilot-operated relief valves.In addition,the dynamic pressure feedback orifice reduces the response speed of the relief valve.This study comprehensively considers the stability,rapidity,and immunity of relief valves and expands current investigations into the dynamic characteristics of relief valves from the perspective of classical control theory,thus revealing the importance of different parameters.

Integration of measurement and simulation of film pressure for estimating deformation of a glass sheet on a noncontact air conveyor

Recently,large and thin glass substrates are transported by air film conveyors to reduce surface damage.On the production line,the glass substrates are desired to be transported flatly on the conveyor to ensure the quality inspection.A method by feedbacking film pressure to the theoretical model is proposed for estimation of the deformation of the glass sheet,and the validity of the method is theoretically and experimentally verified.First,a theoretical model including the flow behavior through a porous-walled gap is established,and the film pressure distribution can be predicted by solving the model.Then,an experimental setup that can simultaneously measure the film pressure and the flatness of the glass sheet is established,and,the validity of the model is verified experimentally.Next,with the pressure points at the grooves as the boundary and the pressure points at the flange area as the feedback,an algorithm is applied to shape the one-dimensional deformation at the centerlines in accordance with a quadratic curve.Furthermore,two-dimensional deformation of the glass sheet can then be estimated by an interpolation operation.Comparisons of the calculated results with the experimental data verify the effectiveness of the estimating method.

Effects of the geometrical parameters of the injection nozzle on ethylene-air continuous rotating detonation

Compared with traditional isobaric combustion,continuous rotating detonation(CRD)has been theoretically proved to be a more efficient combustion mode with higher thermal cycle efficiency.However,the realization and stable operating of liquid kerosene detonation is still a challenge.As a major component of kerosene pyrolysis products after regenerative cooling,ethylene is a transitional hydrocarbon fuel from kerosene to hydrogen and it is worth studying.In this paper,a series of 2 D numerical simulations are conducted to investigate the effects of the injection nozzle on the ethylene-air CRD.Three geometrical parameters of the nozzle are thoroughly tested including the distance between two neighboring nozzle centers,the nozzle exit width,and the slant angle of the nozzle.The results show that an ethylene-air detonation wave is realized and it propagates stably.A small distance between two neighboring nozzle centers is conducive to improving the strength of the CRD wave and leads to greater feedback pressure into the plenum.As the nozzle exit width increases,the strength of the CRD wave and the feedback pressure into the plenum both increase.The CRD wave propagation velocity is greatly improved and the feedback pressure into the plenum is significantly reduced when the slant angle of the nozzle is positive.By contrast,a sizeable reduction in velocity is found when the angle is negative.The co-rotating two-wave propagation mode is observed when the angle is 30°,and the highest CRD propagation velocity and the lowest feedback pressure are both obtained when the angle is 60°.