液壓橫移式加熱爐出鋼機設計含9張CAD圖,液壓,橫移式,加熱爐,出鋼機,設計,cad CHINESE JOURNAL OF MECHANICAL ENGINEERING Vo1.22，No.1，2009 DOI：10．3901／CJME．2009．01．109，available online at www.cjmenet.com；www.cjmenet.com.cn Water Hydraulic 2／2 Directional Valve with Plane Piston Structure GONG Yongjun，YANG Huayong ，and WANG Zuwen 1 Laboratory of Fluid Power Transmission and Control Dalian Maritime University,DaLian 116026,China 2 The State Key Lab of Fluid Power Transmission and Control Zhejiang University,Hangzhou 310027,China Received July 13，2008；revised November 19，2008；accepted December 3，2008；published electronically February 20，2009 Abstract： Due to the fire resistance and environmental compatibility，using water as the working fluid in hydraulic circuits is receiving an increasing attention by both manufactures and users．This hydraulic directional valve is developed．When new water hydraulic directional valve is designed and manufactured，this paper introduces a water hydraulic 2／2 directional valve and its principle．The valve is composed of a hydraulically operated seat valve and a magnetic 3／2 direction valve．Aimed at the serious leakage and impact generating easily in reversing suddenly, an improved structure of water space seal is changed to direct seal，compaction force between main valve spool and main valve pocket was logically designed and damper in pilot valve port is matched with sensitive cavity in main valve．From the view of flow control，the methods of cavitations resistance of the directional water hydraulic valve are investigated．The computational fluid dynamics approaches are applied to obtain static pressure distributions and cavitations images in the channel of the main stage of the valve with two kinds of structure． The results show that the method of optimized spout can effectively restrain cavitations．The work provides some useful reference for developing water hydraulic control valve with the lower noise and lower vibration．Meantime，the structural parameters are optimized on the basis of information obtained from simulation．Static test，dynamic test and life test are accomplished，and the results show that the water hydraulic directional valve possesses good property, its pressure loss is 1.1MPa lower, switching time is shorter than 0.025 s．a(chǎn)nd its strike crest is 0.8MPa lower．The valve possess fine dynamic performance with the characteristic rapidly action and lower impulsion． Key words：water hydraulic，directional valve，structure optimization，flow field analysis 1 Introduction For its abundant transmission media．Environmentally friendly, clean and safe，fire resistant，and so on，water hydraulic technology has been turned out to be a focus of research in the field of fluid power transmission and control〔l〕． Water hydraulic valve． as one of the key components，is studied extensively． The traditional oil hydraulic directional valve is of spool pilot valve，rotary valve or cone valve．Although the unbalance force on the rotary valve and the pilot pool valve are weak，the force to operate them are weaker and the leakage are usually bigger with a larger tolerance for the relative movement of the valves and valve seats For its low viscosity．the loss of leakage of water hydraulic system is much higher．For the same clearance and pressure，the loss of leakage of the water hydraulic system is several decade times that of oil hydraulic system ． In order to maintain a reasonable low leakage the clearance should be extremely small，which may lead to difficulty of machining．a(chǎn)t the same time．it is easily for the moving parts to be choked and stuck． As for the cone valve．a(chǎn)lthough has a smaller leakage，unbalanced axial fore on the valve exist，so a stronger force is needed to operate it ． For the incompressible and high stiffness，the hydraulic shock of the water hydraulic directional valve is more serious ． So how to lessen the leakage．how to realize direction change with low or even no hydraulic shock and how to improve its static and dynamic characteristic are the key issues of study． So far-there is no report on the study of water hydraulic directional valve. In this Paper，a new serial of water hydraulic valves has been provided based on the change of seal pattern，reasonable design of pre-tightening force，and optimization of the flow passage． 2 Experimental Working Principle of the Water Hydraulic Directional Valve Fig.1 shows the water hydraulic directional valve．It is electro—hydraulic directional valve．The pilot stage is a 2／3 electromagnetic directional ball valve．Being different from traditional oil hydraulic valve．a(chǎn) valve pocket is added to the main valve，and the main valve pocket is over fitted to the valve body．The main valve spool is fitted to the main valve pocket，and the surface sealing is achieved by the plane of the valve．Lip-type packing are set in both ends to achieve no leakage．The spring is for compensation of the frictional force．Both ends of the main valve spool are supported radically by bushes， which are made of wear-resisting materials， so the problem of abrasion is settled in this way． Fig.1． Sketch of water hydraulic directional valve structure The structural principle of the valve is as follows: there is damper at the valve port，two dampers in series act as half bridge resistant，and the controlling rib connects to the sensitive chamber on the right side of the valve by the central hole. When the electromagnet is out of power, main valve spool is moved to the right under the force of inlet, at the same time，water in the sensitive chamber is discharged through the pilot valve，and the main valve is open．When the electromagnet is charged．water for control is inducted to the sensitive chamber, and the main valve spool is compressed on the valve pocket．a(chǎn)nd the main valve is shut down． 2.1 Design of the pressing force of main valve spool The contact surface of the main valve spool and the valve pocket is plane，there maintains a certain pressing force between them (Fig.2).The pressing force varies according to the change of control fluid pressure，the higher pressure is，the bigger the pressing force will be．Therefore，leak age between the main valve spool and the valve pocket is nearly zero．The stress condition of the main valve spool is as follows． Fig.2． Sketch of axial force of main valve spool Suppose that the inlet pressure of the main valve is p，and pressure loss is neglected，so the pressing force of the main valve is p1,，we have It is obvious that p1 is positive，which ensures that the main valve spool is pressed against to the valve pocket．If pl is too weak，there will be leak age between the main valve spool and the valve pocket，and if pl is too high，the force for directional change will be bigger and abrasion between the main valve spool and the valve pocket will occurs．According to our experiments，the facial contact force for the main valve spool an d the valve pocket is at best 2 times the inlet pressure P．In the process of design，it is required that 2.2 Meshing design of pilot valve damper and sensitive chamber For the design of directional valve． it is not only necessary for a quick directional change，but also a minimal hydraulic shock．So a dam per is set at the inlet of the pilot valve，two dampers in series act as half bridge resistant，a throttle backing pressure is then built up at the end of the main valve，which has a function of retardation and speed-regulation．Provided at any time, there is even pressure in the sensitive chamber an d the compressibility of the fluid omitted，equations will be acquired as follows： Where F is exterior force，f is frictional force，k is the stiffness of the spring，x is buffer distance，Ps is pressure of the sensitive chamber, Ad is area of the main valve spool end， m is the mass of main valve spool， a is shock accelerated velocity,△p is differential pressure between imports and exports of dam per,A0 is flow area of the damper, v is shock velocity, qv is flow of the damper, cq is coefficient of discharge of inundated port′s efflux． From Eqs.(3)-(7)，the characteristic expression of the pilot valve port is deduced．When shock energy is too big and throttling area is too small．shock is rather strong and can create bigger front—shock hump， and buffer effectiveness is not good；when the shock energy and throttling area are too big，shock is weak，buffering force is smaller, and residual velocity can exist which may create correlation equation assumed by Launder, the aeolotropism and eddy flow of turbulent current can be well predicted．packet oil phenomenon and bigger back-shock hump at the This paper uses Anisotropic k-ε model to simulate flow end of the shock．Therefore，in the case of proper design，it is required that the damper should match with sensitive chamber，and the damper should have good performance and linearity．According to experience，linearity of the damper should be less than 30％ ． 3 Flow Field Simulations and Analysis When the directional valve is being designed． Its pressure loss should be as small as possible．Pressure loss of the directional valve usually is determined by experiment．Development of calculated hydromechanics provides a scientific approach to calculate pressure loss of the directional valve with complex flow passage．It turned out to be an effective method to make use of numerical calculation， with which optimization of the movement，flow and structure of the hydraulic component can be done． 3.1 Mesh division The mesh of water hydraulic directional it′s main valve passage is shown in Fig．3．Main valve passage is three—dimensional symmetrical structure， the passage′s three—dimensional model is used for mesh division and flow field calculation in the study． Fig．3． Mesh of main valve flow passage Because area gradient of flow field of the computational domain varies greatly, for the purpose of improving calculation accuracy and reducing amount of calculation work，the computational domain has been divided into multiple small sectors．Initial computational mesh is created in Gambit．In high speed domain of the main valve port and nearby, velocity gradient is very big，and complex flow pattern exists，better structuring meshes in this domain and coarser unstructured meshes in other area are applied． 3．2 Mathematic model 3．2．1 Anisotropic k-ε turbulent model Because Anisotropic k-εmodel adopt Reynolds stress correlation equation Assumed by Launder, the aeolotropism and eddy flow of turbulent current can be well predicted. This paper uses Anisotropic k-ε model to simulate flow pattern of flow field of the directional valve′s main valve，calculation equation of its turbulent kinetic energy k and turbulent dissipated energyε is as follows： Calculation equation of turbulent current frequency ω is Where，ui′ is fluctuation velocity sector in i direction ， uj′is fluctuation velocity component in the J direction，P is fluid density, and μ is absolute viscosity． 3.2.2 Cavitations model Gas phase volume percent equation can be expressed as where，a is gas phase，aa is gas phase volume percent，Pa is gas phase density．l is fluid phase．Pl=998.2 kg／m 3 (fluid phase density)，and l-aa is fluid phase volume percent．Mean density ρ is And mal，is mass transfer between gas phase and fluid phase due to cavitations，it is expressed as where Pv is vaporization pressure；n is number of bubbles per unit volume；R is bubble radius which is expressed as 3.3 Simulation results and analysis 3.3.1 Flow characteristic analysis Numerical calculation is carried out with Fluent software．In the calculation there are some assumptions as follows． Reynolds stress The fluid is uncompressible，flow is of thermal insulation，and there is no slip on the wal1．Suppose that the opening of valve port is 4 mm．the inlet flow is 120 L／min．a(chǎn)nd the outlet pressure is the pressure of working water circuit，whose absolute pressure is 1MPa． Fig.4 shows the static pressure isoline along axial symmetry plane in the flow passage of the main valve．It can be seen that at the nozzle between the main valve spool and main valve pocket．the pressure contour is denser and pressure drop is bigger, which lowered to 0.7MPa． Fig．4． Pressure isoline of main valve flow passage(MPa) Fig．5 shows the velocity vector distribution along axial symmetry plane in main valve flow passage．It can be seen that after fluid enter chamber, spiral vortex is formed near the main valve spool comer, its central pressure is lower, and spiral vortex dissipates fluid kinetic energy by viscous friction． Fig．5． Velocity vector distribution of main valve 3.3.2 Structure optimization and flow field analysis On the basis of the analysis above，at the nozzle formed by the main spool and main valve pocket，the fluid will diffuse or shrink suddenly as is limited by the structure．which may cause the streamline changing sharply, spiral vortex appeared on the comer point will dissipate the kinetic energy of the fluid．a(chǎn)ll of which will cause great pressure 1oss． In order to improve the performance of water hydraulic directional valve．the structure of nozzle has to be optimized． Fig．6 shows the comparison of flow passage before and after optimization．In order to make the streamline smooth，the optimized valve spool is manufactured to be arc transitional surface，which voids appearance of death angle． Fig．6． Comparison of flow passage before and after optimization Simulation and computation of flow passage of the optimized main valve have been done under the same condition．a(chǎn)nd the pressure distribution in axial symmetry plane is shown as Fig．7．It can be seen that at the nozzle where fluid flows into the chamber, the density of pressure isoline decreases，pressure gradient reduces，and pressure loss reduces to 0.3MPa after the structure is optimized． Fig．7． Pressure isoline of flow passage after optimization(MPa) The distribution of velocity vector after optimization along with axial symmetry plane is shown as Fig．8． Fig．8． Velocity vector distribution of flow passage after optimization There is no spiral vortex on the corner point of main valve near the nozzle，so the optimized structure effectively restrains the appearance of low pressure area in the fluid field． 4 Experiment and Data Analysis 4．1 Experiment device and method The water hydraulic directional valve designed is made of stainless materia1．its rated pressure is 14 MPa．a(chǎn)nd maximum flow up to 120 L／min．In order to prove the correction of design principle and simulation results, experiments on both static and dynamic characteristics of the valve have been done．The experiment method refers to related national standard GB 8106—87 of similar experiments of oil hydraulic directional valve The experiment has been done on the test rig of State Key Laboratory of Fluid Power Transmission and Control of ZheJiang University,China．a(chǎn)s is shown in Fig.9． Fig．9． Test rig of water hydraulic components Fig．10 shows the schematic diagram of this experiment．As the medium of water is strongly corrosive， all components of this system are of stainless materials． Fig．10． Test principle of water hydraulic directional valve 1．Conversion 2．Conversion motor 3． Tap water hydraulic pump 4．Filter 5．Relief valve 6．Thermometer 7． Pressure transducer 8．Valve tested 9．One—way throttle 1 0．Flow meter During the experiment， relief valve 4 regulates the entrance pressure of the valve being checked，rotation speed of the variable·frequency electric motor 2 is regulated by frequency—transformer 3，which adjusts the discharge flow of water hydraulic pump 1．The outlet backing pressure of the valve 9 is adjusted by one—way throttle valve 8 and is measured by flow meter． 4.2 Experiment results 4.2.1 Flow-pressure difference experiment of water hydraulic directional valve In the experiment of pressure loss．relief valve 4 serves as safety valve whose safety pressure is 18MPa．The valve tested is charged and then its spool is on the position of through—flow．To make the amount of fluid flowing through the valve 9 increase gradually from zero to rated flow by adjusting the discharge flow of water hydraulic pump，and choose several points to measure each point′s discharge pressure， based on which the valve′s flow-Pressure difference performance curve can be achieved．The outlet backing pressure of the valve tested 9 can be adjusted by one—way throttle valve 8．The value of the flow is read out on the flow meter 1 0，the pressure of inlet and outlet display on the indicating instrument of pressure transducer 7．Comparison of the characteristic of flow．Pressure difference between the result of simulation and experiment is shown as Fig.11． Fig.11． Characteristic curve of qv——△p From Fig.11，it can be seen that，for qv<15 L／min，the pressure difference between inlet and outlet results from the flow passage of pilot ball valve and increases notably as the flow increases；for qv>=l5 L／min，the pressure difference between inlet and outlet mainly results from the main valve passage and increases slowly almost like a linear as the flow increases． In addition，the test result is bigger than the simulation result．This is because the pressure loss in the test is the sum of the pressure loss of main valve and pilot valve． while the optimized result from simulation and computation only includes the pressure loss of main valve． From the comparison of the structure of main valve before and after optimization，it can be noticed that the optimized pressure loss of main valve decreases notably． Attention should be paid to that for qv< 30 L／min the result of simulation shows that the pressure loss between inlet and outlet decreases as the flow increases；however, this case does not appear, which indicates that there is much discrepancy for the simulation when the flow is smal1． 4.2.2 Experiment of dynamic characteristics of water directional valve Adjust the overflow valve 4 and one—way throttle valve，make the pressure of inlet Pi of the tested valve 9 be the rated pressure 14MPa，and the pressure of outlet P。be the given backing pressure， the amount of fluid flowing through the tested valve is 80％ of maximum flow．Then charge and discharge the tested valve under rated voltage and the data acquisition system picks the dynamic response curve of the tested water hydraulic directional valve．a(chǎn)s is shown in Fig.12． Fig．12． Dynamic response curve of water hydraulic directional valve From Fig.12，the pressure decreasing time t1 is smaller than 0.05 s．the pressure increasing time t2 is smaller than 0.05 s．a(chǎn)nd the charging time and discharging time are almost the same． The direction change is quick， the pressure peak△ produced while reversing is decrease 6％ ，and the reversing shock is small，which indicates good dynamic response characteristics． 4．2．3 Experiment on the life of water hydraulic directional valve Respectively set the pressure of inlet pressure of the tested valve to be variable value and the pressure of outlet P。to be remained the specified backing pressure and the amount of fluid flowing through the tested valve to be 100 L／min， continuously charge and discharge the electromagnet of the tested valve up to l0000 times，and then check the main components of the tested valve，there should be no damage inordinate wear．Figs．13(a)，13(b)show the response curve of continuous directional change under pressure of 12MPa and 14MPa． It is clarified that the dynamic responsive characteristics of the valve are nearly uniform，and direction change is reliable and prompt． 5 Conclusions (1)This new water hydraulic directional valve′s pressure loss is small under rated condition．a(chǎn)nd its speed of directional change is fast while its hydraulic shock is weak．therefore，good dynamic characteristics are obtained．In the life experiments．the directional valve operates normally, and its direction change is reliable．The performance of this kind is comparable to the same kind oil hydraulic valve． Fig．13. Life test curve of