Optimum Design of Valve Core Structure of Hydraulic Control one-way Valve
In practical applications, the hydraulic control oneway valve, as the core component, should be able to quickly open and fix the load in the stop position for a long time after closing. Therefore, its opening and closing performance and sealing reliability are very important.
Working principle
The structural principle of a certain hydraulic control one-way valve is different from traditional hydraulic control one-way valves. It is installed in pairs between the servo valve and the actuator, locking the oil circuits of the servo valve and the actuator respectively. The K1 cavity and M1 cavity are respectively connected to the servo actuator A1 and B1 cavities, while the K cavity and M cavity are respectively connected to the servo valve A and B cavities, as shown in Figure 1.
Figure 1 Functional schematic diagram of hydraulic control one-way valve
When the pressure at control port H is less than the opening pressure, the valve core is closed, and the sealing ring isolates the oil circuit between K1 chamber and K chamber, M1 chamber and M chamber. The oil circuit between the servo valve and the actuator is disconnected, and the actuator is locked in the zero position. The system is in a non working state.
When the oil circuit is locked, external control pressure is required to overcome spring force and open the oil circuit from the forward direction. When the pressure at control port H reaches the valve opening pressure, K is connected to K1 and M is connected to M1. The oil flows forward through the one-way valve, and the system enters a working state.
When the main oil circuit pressure drops, the control chamber pressure decreases accordingly, and the valve core quickly closes under the action of spring force, locking the oil circuit between the actuator and servo valve.
Original valve core structure
A certain hydraulic control one-way valve previously adopted a type II sealing structure of "GLYD ring+sealing ring". The valve core is an integrated structure, and the circumference contains multiple sealing surfaces. Its structure is shown in
Figure 2. If the installation hole is slender, it is difficult to install the valve core, and its metal edges are prone to damage the sealing ring, causing leakage. In addition, the integrated structure requires a high degree of coaxiality between the valve core and the inner holes of the shell. Once the coaxiality is poor, the sealing performance of all parts of the valve core cannot be guaranteed simultaneously. Therefore, it is necessary to optimize the original valve core structure and conduct experimental verification.
Optimization design of valve core structure
1) Selection of sealing materials
The working medium of the system is aviation hydraulic oil, with a working temperature of -10 ℃ to 180 ℃. Choose a sealing material that is resistant to high temperature, has good elasticity, and is suitable for injection molding and mechanical processing - fluororubber FKM7108.
2) Optimization design of sealing pair
When neglecting the hydraulic pressure, the main causes of leakage can be divided into rough sealing mating surfaces or small sealing ratio pressure (large sealing mating surface clearance). Therefore, there are two methods to improve sealing performance: ① Increase the surface roughness machining accuracy to Ra0.4~Ra0.8 μ m。 Increase the circumferential waviness to achieve labyrinth sealing under the action of sealing force By increasing the contact pressure (i.e. sealing specific pressure) on the sealing surface, the sealing element undergoes elastic deformation and the rear wheel profile peak flattens, resulting in good sealing.
The optimized highly reliable hydraulic control one-way valve adopts a structural form of "conical soft seal+type I seal" to meet different requirements of zero leakage: conical seal, which means that the mating surface between the valve core and the shell valve port is a conical surface, and the sealing form is a conical soft contact; Rolling and bonding vulcanized FKM7108 into the groove of the valve core cone surface to form a sealing ring, forming a sealing pair with the valve port cone surface. Reliable sealing is achieved through the elastic reset trend of rubber.
During the closing process, the conical valve core is pushed by spring force, and the pressure piece contacts the conical valve port. When the valve core is limited by the inverted cone sealing surface, the compression amount and sealing specific pressure of the sealing element reach the maximum, and the valve core is pressed to the tightest position to achieve complete closure, as shown in Figure 3.
pressure inside the actuator and spring force superimpose on the valve core after the valve is closed. The higher the residual pressure of the actuator, the closer the sealing strip is to the small end of the conical valve port, and the greater the compression and sealing pressure of the sealing element, which actually improves the sealing reliability.
Therefore, the sealing structure not only avoids damage to the valve core and sealing ring, but also improves the sealing pressure and reliability in the closed state.
The optimized highly reliable hydraulic control one-way valve consists of a shell, a stop, a valve core, a sealing ring, a spring,
and screws, as shown in Figure 4. The valve core adopts a self balancing structure to achieve high pressure resistance, and the bidirectional pressure exerted by the servo valve chamber on the valve core can cancel each other out. The split valve core and integrated shell structure make the hydraulic control one-way valve have the advantages of light weight and compact
structure. The basic working principle is that when the control pressure rises and the valve core is opened, the servo valve chamber and the actuator chamber are interconnected; When the control pressure drops, the valve core closes and the actuator chamber and servo valve chamber are isolated from each other.
Flow field simulation and analysis
When the conical soft seal reaches its maximum speed and is impacted, the design of the flow channel structure not only affects the pressure loss of the hydraulic control one-way valve, but also affects the sealing reliability and product life. Therefore, CFD simulation software [2] is used to analyze the impact of the flow field in the flow channel on the seal.
CFD grid partitioning [3-4]:
Import the three-dimensional model of the hydraulic control one-way valve into CFD software for grid division.According to
the structural characteristics of the internal flow channel of the valve, the mesh is refined at complex flow fields (such as the corners of the valve port and flow channel) to achieve accurate and fast solution.
Boundary conditions for simulation calculations [5-7]
(1) The flow of hydraulic oil is adiabatic;
(2) During the flow process of hydraulic oil, the thermal conductivity is constant;
(3) The boundary between the fluid and the wall is a stationary wall;
(4) The hydraulic oil inside the valve is assumed to be an incompressible fluid, and the flow is single-phase;
(5) The flow state is turbulent, using standard κ-ε Two equation turbulence model [5];
(6) Other hydraulic oil parameters used for calculation: density 860 kg/m3, dynamic viscosity 0.27 N/(m • s);
(7) The valve inlet hole K or M is taken as the pressure inlet, and the valve outlet K1 or M1 is taken as the pressure outlet;
(8) Main structural parameters: valve core opening.
Figures 5 and 6 respectively show the simulation diagrams of the flow field pressure, velocity/flow rate, and three-dimensional streamline of the hydraulic control one-way valve.
Figure 5 Flow field pressure simulation diagram
Figure 6 Speed/Flow and 3D Streamline Simulation Diagram
Mechanical analysis of conical sealing valve core
When the valve core is in a force balanced state, it is only affected by control pressure, spring force, return oil pressure, and shell support force. The force balance equation is as follows:
Test verification
asealing test of the rest are completed on the loaded engine. Under the specified test conditions, the actuator can retract normally and be able to fix its position normally. The results indicate that the sealing and opening/closing characteristics of the hydraulic control one-way valve can meet the system requirements.
conclusion
of the sealing part, facilitating product optimization and improvement [10-11];
(2) When designing a highly reliable hydraulic control one-way valve, a fluororubber FKM7108 and metal integrated design was adopted. This valve has the characteristics of compact structure and light weight. By optimizing the valve core structure, the sealing performance and system reliability have been improved, ensuring that the hydraulic load can be locked in any position for a long time in harsh environments. This valve core structure has certain reference significance for other valves and has broad application prospects.