1. Introduction

2. Structure and modeling of the HLHMDCUV

2.2. Valve initial structural parameters

This paper designs and analyzes the HLHMDCUV. The rated pressure is 40 MPa, the rated flow rate is 1200 L/min, the density of emulsion is 890 kg/m³, and the dynamic viscosity of emulsion is 0.792×10^-3 Pa·s. Based on the structural design and characterization, the initial structural parameters of HLHMDCUV are shown in Table 1.

The initial structural parameters are input into the two AMESim models shown in Figure 2, and the simulation duration is 40 s in total, using the signals shown in Figure 3 to simulate the action of a section of the hydraulic bracket; the variable throttle valve is completely closed at 0~10 s to simulate that the hydraulic bracket does not need to use fluid; the variable throttle valve is open at 10~30 s to simulate that the hydraulic bracket uses fluid; the variable throttle valve is closed at 30~40 s to simulate that the hydraulic bracket The variable throttle valve closes at 30~40 s, simulating that the hydraulic support does not need to use liquid. The following results can be obtained, as shown in Figure 4, Figure 5, Figure 6 and Figure 7.

In the case of the same parameters, as shown in Figure 4, in 0~10 s, the hydraulic support does not need to use liquid, the two forms of HLHMDCUV outlet pressure is equal, at this time, the pumping station system has just been started, there is no external signal interference, indicating that the two forms of static performance is the same, at this time, the unidirectional main spool of the HLHMDCUV is closed, the unloading of the main spool is completely open, the emulsion pump is in the state of complete unloading. At 10~30 s, the hydraulic bracket suddenly uses emulsion, and the outlet pressure of both forms drops to the lowest point in the same way, at this time, the unloading main valve spool of HLHMDCUV closes, and the emulsion pump supplies emulsion to the hydraulic bracket. At about 15 s, the HLHMDCUV outlet pressure of form b is the first to rise and quickly reaches the set value of 40 MPa with almost no overshooting, and then the pressure is steadily maintained at the set value; whereas, the HLHMDCUV outlet pressure of form a rises later than that of form b, and the rate of rise is lower than that of form a. There is 10% overshooting, which suggests that the dynamic performance of form b is inferior to that of form a. Figure 5 is the enlarged diagram of Figure 4 at 30 s. It can be seen that the variable throttle valve suddenly closes at 30 s, i.e., when the hydraulic bracket suddenly does not use the emulsion, the pressure pulsation is generated in the emulsion supply system, and both forms of HLHMDCUV complete the pressure unloading of the emulsion supply system within 0.1 s, and then maintain the pressure stability within the emulsion supply system within 10 s. The pressure is also stabilized within the emulsion supply system.

From Figure 6 and Figure 7, it can be seen that the inlet pressure of the HLHMDCUV of form a is very small and almost zero during unloading, while the inlet pressure of the HLHMDCUV of form b is only slightly lower than the outlet pressure during unloading. It means that when the HLHMDCUV causes the emulsion pump to unload, form a causes the pump to consume less energy and the system saves more energy.

Comprehensive comparison, the two installation forms of HLHMDCUV in the face of the hydraulic support conditions change, can quickly respond and maintain the pressure stability of the fluid supply system, reducing the traditional mechanical unloading valves and electromagnetic unloading valves frequent opening and closing of the pressure pulsation brought about by the unloading valve. While better dynamic performance can be obtained with form a, the performance difference between the two is only within 3 s. According to statistics in the coal mine generalized mining face normal work, emulsion pumping station in the unloading state of time occupies almost 80% of the entire working hours. That means HLHMDCUV needs to be unloaded for a long period of time during normal working hours at the generalized mining face of the underground coal mine. If HLHMDCUV adopts the installation method of form a, the emulsion pump is in the state of high load and high power consumption for a long time, which wastes huge electric energy and accelerates the damage of the emulsion pump, which is far away from the design intention of this paper, and also contrary to the purpose of the construction of the intelligent mine. Therefore, in this paper, the mounting form b is used for the subsequent research and application of HLHMDCUV.

Figure 3. Setting value of variable throttle opening.

Figure 3. Setting value of variable throttle opening.

Figure 4. Outlet pressure of HLHMDCUV.

Figure 4. Outlet pressure of HLHMDCUV.

Figure 5. Localized enlargement of HLHMDCUV outlet pressure diagrams.

Figure 5. Localized enlargement of HLHMDCUV outlet pressure diagrams.

Figure 6. Inlet and outlet pressures for form a.

Figure 6. Inlet and outlet pressures for form a.

Figure 7. Inlet and outlet pressures for form b.

Figure 7. Inlet and outlet pressures for form b.

2.1.2. Creo Simulation Model

In order to study the internal flow field distribution of the unloading valve during the working process, the flow field model of the relief valve was established by using the computational fluid dynamics (CFD) analysis method . Pressure, velocity and turbulent kinetic energy distributions of the unloading valve during the opening process and steady state are simulated and analyzed. The structural parameters affecting the performance and reliability of the unloading valve are directly obtained from internal cloud and streamline diagrams. Using the data obtained in the previous section, this paper uses Creo to model the unidirectional main spool, unloading main spool, digitally controlled pilot valve and unloading pilot valve of HLHMDCUV. As shown in Figure 8.

2.3. Mathematical modeling of the HLHMDCUV

As shown in Figure 9, the dynamic mathematical model of the unloading valve is based on two basic principles. force balance and flow continuity. In order to highlight the main influencing factors and achieve model simplicity, the following analysis ignores the secondary factors such as the liquid resistance of the over-liquid orifice. The mathematical model is described by the following equation.

(1) The differential equation of motion of the unloaded main spool, the

$${\mathrm{p}}_1{\mathrm{A}}_1-{\mathrm{p}}_2{\mathrm{A}}_2={\mathrm{m}}_1\frac{{\mathrm{d}}^2\mathrm{y}}{\mathrm{d}{\mathrm{t}}^2}+{\mathrm{B}}_1\frac{\mathrm{dy}}{\mathrm{dt}}+{\mathrm{K}}_1\left({\mathrm{y}}_0+\mathrm{y}\right)+{\mathrm{F}}_{\mathrm{f}}+{\mathrm{F}}_{\mathrm{t}}+{\mathrm{F}}_{\mathrm{s}}$$

(1)

where ${\mathrm{F}}_{\mathrm{s}}$ is steady state hydrodynamic force acting on the main valve, the

$${\mathrm{F}}_{\mathrm{s}}={\mathrm{C}}_{\mathrm{d}1}\mathsf{\pi }{\mathrm{D}}_1{\mathrm{p}}_1\mathrm{ysin}2{\mathsf{\alpha }}_1$$

(2)

${\mathrm{F}}_{\mathrm{t}}$ is transient hydrodynamic forces acting on the main valve, the

$${\mathrm{F}}_{\mathrm{t}}={\mathrm{L}}_1{\mathrm{C}}_{\mathrm{d}1}\mathsf{\pi }{\mathrm{D}}_1\sin {\mathsf{\alpha }}_1\sqrt{2\mathsf{\rho }{\mathrm{p}}_1}\frac{\mathrm{dy}}{\mathrm{dt}}$$

(3)

${\mathrm{F}}_{\mathrm{f}}$ is friction between the main spool and the valve body, the

$${\mathrm{q}}_1={\mathrm{C}}_{\mathrm{d}1}\mathsf{\pi }{\mathrm{D}}_1\mathrm{ysin}{\mathsf{\alpha }}_1\sqrt{\frac{2}{\mathsf{\rho }}{\mathrm{p}}_1}$$

(4)

(2) The differential equation of motion of the spool of a mechanically unloaded pilot valve, the

$${\mathrm{p}}_{\mathrm{k}}{\mathrm{A}}_{\mathrm{k}}={\mathrm{m}}_2\frac{{\mathrm{d}}^2\mathrm{x}}{\mathrm{d}{\mathrm{t}}^2}+{\mathrm{B}}_2\frac{\mathrm{dx}}{\mathrm{dt}}+{\mathrm{K}}_2\left({\mathrm{x}}_0+\mathrm{x}\right)+{\mathrm{F}}_{\mathrm{s}2}+{\mathrm{F}}_{\mathrm{t}2}$$

(5)

where ${\mathrm{F}}_{\mathrm{s}2}$ is steady state hydrodynamic force acting on the pilot valve, the

$${\mathrm{F}}_{\mathrm{s}2}=2{\mathrm{C}}_{\mathrm{d}2}\mathsf{\pi }{\mathrm{D}}_2{\mathrm{h}}_0\frac{\mathrm{x}}{\mathrm{R}}{\mathrm{p}}_2\cos \mathsf{\theta }$$

(6)

${\mathrm{F}}_{\mathrm{t}2}$ is the transient hydrodynamic force acting on the pilot valve, the

$${\mathrm{F}}_{\mathrm{t}2}={\mathrm{L}}_2{\mathrm{C}}_{\mathrm{d}2}\mathsf{\pi }{\mathrm{D}}_2{\mathrm{h}}_0\frac{2}{\mathrm{d}}\sqrt{2\mathsf{\rho }{\mathrm{p}}_2}\frac{\mathrm{dx}}{\mathrm{dt}}$$

(7)

where, ${\mathrm{h}}_0=\sqrt{{\left(\frac{\mathrm{d}}{2}\right)}^2-{\left(\frac{{\mathrm{D}}_2}{2}\right)}^2}$

(3) The flow equation through the mechanical unloading pilot valve orifice, the

$${\mathrm{q}}_2={\mathrm{C}}_{\mathrm{d}2}\mathsf{\pi }{\mathrm{D}}_2{\mathrm{h}}_0\frac{2\mathrm{x}}{\mathrm{d}}\sqrt{\frac{2}{\mathsf{\rho }}{\mathrm{p}}_2}$$

(8)

(4) Differential equations of motion for one-way valves, the

$$\left({\mathrm{p}}_1-{\mathrm{p}}_2\right){\mathrm{A}}_{\mathrm{A}}={\mathrm{m}}_{\mathrm{A}}\frac{{\mathrm{d}}^2{\mathrm{x}}_{\mathrm{A}}}{\mathrm{d}{\mathrm{t}}^2}+{\mathrm{B}}_{\mathrm{A}}\frac{\mathrm{d}{\mathrm{x}}_{\mathrm{A}}}{\mathrm{dt}}+{\mathrm{K}}_{\mathrm{A}}{(\mathrm{x}}_{\mathrm{A}0}+{\mathrm{x}}_{\mathrm{A}})+{\mathrm{F}}_{\mathrm{tA}}+{\mathrm{F}}_{\mathrm{sA}}$$

(9)

where ${\mathrm{F}}_{\mathrm{sA}}$ is steady state hydrodynamic force acting on the one-way valves, the

$${\mathrm{F}}_{\mathrm{sA}}={\mathrm{C}}_{\mathrm{dA}}\mathsf{\pi }{\mathrm{D}}_{\mathrm{A}}\left({\mathrm{p}}_1-{\mathrm{p}}_2\right){\mathrm{x}}_{\mathrm{A}}\sin 2{\mathsf{\alpha }}_{\mathrm{A}}$$

(10)

${\mathrm{F}}_{\mathrm{tA}}$ is transient hydrodynamic forces acting on the main valve, the

$${\mathrm{F}}_{\mathrm{sA}}={\mathrm{C}}_{\mathrm{dA}}\mathsf{\pi }{\mathrm{D}}_{\mathrm{A}}\left({\mathrm{p}}_1-{\mathrm{p}}_2\right){\mathrm{x}}_{\mathrm{A}}\sin 2{\mathsf{\alpha }}_{\mathrm{A}}$$

(11)

(5) One-way main valve orifice flow equation, the

$${\mathrm{q}}_{\mathrm{A}}={\mathrm{C}}_{\mathrm{dA}}\mathsf{\pi }{\mathrm{D}}_{\mathrm{A}}{\mathrm{x}}_{\mathrm{A}}\sin {\mathsf{\alpha }}_{\mathrm{A}}\sqrt{\frac{2}{\mathsf{\rho }}\left({\mathrm{p}}_1-{\mathrm{p}}_2\right)}$$

(12)

(6) The differential equation of motion of the solenoid proportional relief pilot valve spool, the

$${\mathrm{p}}_3{\mathrm{A}}_3={\mathrm{m}}_1\frac{{\mathrm{d}}^2\mathrm{y}}{\mathrm{d}{\mathrm{t}}^2}+{\mathrm{f}}_1\frac{\mathrm{dy}}{\mathrm{dt}}+{\mathrm{K}}_{\mathrm{m}}\mathrm{i}+{\mathrm{F}}_{{\mathrm{f}}_1}+{\mathrm{K}}_{{\mathrm{e}}_1}{\mathrm{x}}_0{\mathrm{p}}_2$$

(13)

(7) The flow continuity equation for a digitally controlled pilot valve, the

$${\mathrm{C}}_2\sqrt{{\mathrm{p}}_1-{\mathrm{p}}_2}-\mathrm{b}{\mathrm{x}}_0\sqrt{{\mathrm{p}}_2}=\frac{{\mathrm{V}}_3}{\mathrm{E}}\frac{\mathrm{d}{\mathrm{p}}_2}{\mathrm{dt}}+{\mathrm{A}}_3\frac{\mathrm{dy}}{\mathrm{dt}}$$

(14)

where ${\mathrm{p}}_1$、${\mathrm{p}}_2$ are the liquid pressure in the upper and lower cavities of the unloading main valve spool respectively, in Pa.

${\mathrm{p}}_{\mathrm{A}}$、${\mathrm{p}}_{\mathrm{k}}$ are the load pressure and the fluid pressure in the front chamber of the control piston, respectively, in Pa.

${\mathrm{A}}_1$、${\mathrm{A}}_2$ are the effective area of the upper and lower cavities of the main spool respectively, in m².

${\mathrm{A}}_{\mathrm{c}}$、${\mathrm{A}}_{\mathrm{A}}$、${\mathrm{A}}_{\mathrm{k}}$ are he effective area of the mechanical unloading pilot valve, the effective area of the one-way valves, and the effective area of the control piston, respectively, in m².

${\mathrm{D}}_1$、${\mathrm{D}}_2$、${\mathrm{D}}_{\mathrm{A}}$ are outlet diameter of the unloading main valve, outlet diameter of the mechanical unloading pilot valve, and outlet diameter of the one-way valves, respectively, in m.

${\mathrm{d}}_1$、${\mathrm{d}}_2$ are diameter of the damping hole of the unloading main valve, and the diameter of the damping hole between the one-way valves and the control piston, respectively, in m.

${\mathrm{L}}_1$、${\mathrm{L}}_2$、${\mathrm{L}}_{\mathrm{A}}$ are damping orifice length of the unloading main valve, damping orifice length of the mechanical unloading pilot valve, and damping orifice length between the one-way valves and the control piston, respectively, in m.

${\mathsf{\alpha }}_1$、${\mathsf{\alpha }}_2$ are half cone angle of unloading main valve, half cone angle of one-way valves, respectively.

${\mathrm{C}}_{\mathrm{d}1}$、${\mathrm{C}}_{\mathrm{d}2}$、${\mathrm{C}}_{\mathrm{dA}}$ are flow coefficient of unloading main valve, pilot valve, one-way valves orifice, respectively.

${\mathrm{C}}_{\mathrm{d}10}$ is flow coefficient of the damping orifice of the unloading main valve, respectively.

${\mathrm{q}}_1$、${\mathrm{q}}_2$、${\mathrm{q}}_3$ are the relief flow rate of the unloading main valve, the relief flow rate of the mechanical unloading pilot valve, and the relief valve of the one-way valves, respectively, in ${\mathrm{m}}^3/\mathrm{s}$;

${\mathrm{B}}_1$、${\mathrm{B}}_2$、${\mathrm{B}}_3$ are opening volume of unloading main spool, opening volume of mechanical unloading pilot spool, opening volume of one-way valves, respectively, in m.

y、x、${\mathrm{x}}_{\mathrm{A}}$ are opening volume of the unloading main valve, opening volume of the mechanical unloading pilot valve, and opening volume of the one-way valves, respectively, in m.

${\mathrm{K}}_1$、${\mathrm{K}}_2$、${\mathrm{K}}_{\mathrm{A}}$ is spring stiffness of the unloading main valve, spring stiffness of the mechanical unloading pilot valve, spring stiffness of the one-way valves, respectively, in N/m.

${\mathrm{m}}_1$、${\mathrm{m}}_2$、${\mathrm{m}}_{\mathrm{A}}$ is mass of unloaded main spool, mass of mechanically unloaded pilot spool, mass of check spool, respectively, in kg.

${\mathrm{F}}_{{\mathrm{f}}_1}$ is digitally controlled pilot valve coulomb friction.

${\mathrm{x}}_0$ is digitally controlled pilot valve displacement.

${\mathrm{p}}_3$ is digitally controlled pilot valve cavity pressure.

${\mathrm{f}}_1$ is digitally controlled pilot spool viscous damping coefficient.

${\mathrm{K}}_{\mathrm{m}}$ is current-force gain.

${\mathrm{K}}_{{\mathrm{e}}_1}$is digitally controlled pilot valve hydrodynamic coefficient.

${\mathrm{A}}_3$ is digitally controlled pilot valve effective cross-sectional area.

${\mathrm{C}}_2$ is throttle port flow coefficient in front of pilot valve cavity.

b is digitally controlled pilot valve flow coefficient.

${\mathrm{V}}_3$ is digitally controlled pilot valve liquid chamber volume.

E is modulus of elasticity of emulsion.

${\mathrm{A}}_3$ is digitally controlled pilot valve effective cross-sectional area.

Figure 9. Structure and principle diagram of HLHMDCUV.

Figure 9. Structure and principle diagram of HLHMDCUV.

3. Results and conclusions

4. HLHMDCUV Manufacturing and Applications

4.1. Manufacture of the HLHMDCUV

Based on the actual needs of the working face environment in underground coal mines, under the premise of ensuring safety and reliability, and pursuing the economic benefits of component processing and mine transformation, combined with the theoretical analysis and research in the previous section, HLHMDCUV is designed as a modularized form that is easy to disassemble and assemble, as shown in Figure 29.

In this paper, HLHMDCUV is modularized for easy disassembly and assembly; the spare parts can be replaced in real time when problems are found in the production of coal mines; the safety and reliability of the system is ensured and the service life of the fluid supply system is prolonged without affecting the production in an orderly manner. It has been experimentally tested that a skilled pump station maintenance worker can disassemble the HLHMDCUV upon first seeing it; replacing individual parts can take up to 15 minutes. After only a few training sessions, the maximum time to replace a single part is 5 minutes.

Figure 30. Selected modules of the HLHMDCUV

Figure 30. Selected modules of the HLHMDCUV

After the performance test of the valve, after the completion of the manufacturing of HLHMDCUV sealing performance is good, no external leakage; good dynamic performance, unloading pressure is stable; regulating the pressure range is large, and can be adjusted according to the actual work, the adjustment method is simple and quick; pressure loss is small.

Figure 31. Performance test of HLHMDCUV.

Figure 31. Performance test of HLHMDCUV.

4.2. Application of HLHMDCUV

After installing HLHMDCUV on the simulation test bench of underground hydraulic support and connecting it to the intelligent control system of the test bench, it has been running stably for more than 300 hours.

Figure 32. Downhole working face simulation lab bench with the addition of HLHMDCUV

Figure 32. Downhole working face simulation lab bench with the addition of HLHMDCUV

As can be seen from Figure 33, in the actual use of the process, when the hydraulic support needs to use liquid, the use of HLHMDCUV eliminates the unloading valve outlet, i.e., the pressure fluctuations at the outlet of the pumping station, eliminating the unloading valve noise, whistling; at the same time reduces the pressure impacts received by the liquid supply system, prolonging the service life of the liquid supply system.

In addition, HLHDCUV uses PLC as the controller, which can be accessed to the computer digital control system, transforming the emulsion pumping station and providing support for intelligent transformation of the hydraulic bracket fluid supply system.

5. Conclusion

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