Valve Development Trends-[DE]Doc.Engineer Prof.H. Murrenhoff;Zhang Haiping compilation

A fluid technology system is nothing more than an energy source (pump and compressor), connecting elements such as pipes, valves and accessories, and actuators composed of cylinders and rotary motors, even in some fields, the use of speed regulation Motor to replace the proportional valve [L1] in the signal and energy circuit, but the valve can always be regarded as the heart of fluid technology.

1 Introduction
In modern and fashionable terms, the valve can also be called the Mechatronic System (Mechatronic System), because most valves have an electro-mechanical energy converter. Modern valves combine digital transmission control technology with pressure, flow and spool stroke sensors. It is easy to see that these valves cover all elements of the electromechanical subsystem. But there are still reasons to use vocabulary that is familiar to the fluid technology community.
Why are hydraulic or pneumatic valves so important for fluid technology? In order to answer this question, we must take a look at the tasks undertaken by valves in fluid technology. They are responsible for controlling pressure and flow in hydraulics and mass flow in pneumatics. When working with pressurized and fast fluid technology transmission systems, such as injection molding machines or flight simulators, the pressure and flow are always adjusted by valves to achieve the required speed and force.
In contrast, a mechanical system can convert rotational energy into linear motion through, for example, a screw nut system. This is always accompanied by high forces and wear on these components. There is also noise that cannot be ignored, especially at high speeds. Fluid technology has an obvious advantage: the use of valves to control several to hundreds of kilowatts of power without a life limit. Even higher powers can be controlled with valves. At this time, the valves are used in the signal circuit to adjust the variable mechanism of the pump to improve system efficiency.
The following introduces the latest developments and trends in the development of hydraulic and pneumatic valves.

2. Hydraulic valve
Many improvements can be seen in the hydraulic valve: from the new concept of the essential electro-mechanical converter to a completely new mechanical design; on the other hand, there are also some proven structural forms that have been combined with digital electronic technology . At the same time, modern integrated electronic technology can already be directly connected to the regional bus system. In addition to these developments, some new solutions have emerged, for example, the use of electrolyzed fluids to replace traditional control edges.

2.1 Direct acting valve
Direct-acting valves usually use a proportional solenoid or a linear motor to propel the control spool. In order to obtain good static characteristics, a four-way valve needs four precise control edges. Figure 2.1.1 is a servo valve [B2] where each control edge can be adjusted separately. The stepper motor at the bottom right of the figure rotates the shaft, thereby pushing the center body of the valve. The central body is connected to four adjustable control slide valves each with a control edge. With this structure, the overlap of each opening can be adjusted according to the requirements of the specific application. The shaft generates an actuator-to-valve mechanical feedback to the left end of the spool. This valve is used in machine tools as a stable structure for linear and rotary movements.

Figure 2.1.1 Servo valve with adjustable control edges

Figure 2.1.2 is a spool valve [L2] (10-diameter, 70 liters / min, 70 bar) driven by a piezoelectric crystal developed at IFAS. A piezoelectric crystal can only produce a small displacement, only one thousandth of the length of the crystal. Therefore, a displacement amplifier is required, see the lower half of the figure. This is a hydraulic amplifier filled with liquid silicon, which can amplify the displacement by 40 times. In order to reduce the force required by the drive, the control spool is pressure balanced. Since the spool displacement cannot be measured directly, a special eddy current sensor connected to the spool sleeve was developed. All electronic control parts are in the valve body. In addition, the system also uses two piezoelectric crystal drivers to achieve thermal compensation.

Figure 2.1.2 Spool valve driven by piezoelectric crystal

Figure 2.1.3 shows the frequency response of the valve when the input signal level is 50. The -3 dB limit is 340 Hz and the -900 attenuation limit is 270 Hz. This study shows that this directly driven valve can achieve very impressive dynamic characteristics. In addition to the dynamic characteristics, the piezoelectric crystal drive has an advantage, and it consumes little energy when staying in one position.

Figure 2.1.3 Frequency response

Figure 2.1.4 introduces a valve used in walking hydraulics. The stepper motor replaces the traditional proportional solenoid [B1], and directly adjusts the control spool through a rack. Due to the stepping torque of the stepper motor, it appears as a very rigid system after positioning. Therefore, the spool displacement sensor is no longer needed.

Figure 2.1.4 Stepper motor direct control valve

Figure 2.1.5 illustrates the structure and working principle of the motor with a two-phase stepping motor. Phase A and phase B can achieve 4 steps. Considering that each step pushes the rack to move 0.124mm, it is not difficult to recognize the advantages of this system. Between each step, the system has a very high rigidity, as shown by the tangent of the sinusoid in the force-displacement diagram. This characteristic is not affected by the power supply of the stepper motor and only depends on the positioning torque. Therefore, a position can be maintained without consuming power. In this regard, stepper motors have the same advantages as piezoelectric crystal drives compared to traditional proportional electromagnets.

Figure 2.1.5 Working principle of stepping motor

2.2 Pilot-controlled valve
Pilot-controlled valves are used to improve valve characteristics or increase the amplification ratio from input electrical energy to fluid power. The example shown in Figure 2.2.1 belongs to the first category.

Figure 2.2.1 Pilot control and pressure compensated valve

The valve is pilot controlled and pressure compensated. The graphic symbols are shown in the lower right corner of the figure. The innovative idea hidden in this valve is to avoid the pressure peaks that are common when using traditional valves [Z1]. If the system pressure exceeds the set valve opening pressure, the pilot chamber will be filled with pressure oil, which is equivalent to increasing the preload of the originally set spring. The opening time of the valve is about 300ms. At the same time, the valve acts as a damper in the circuit due to leakage.
A typical pressure valve will have a pressure spike during a pressure step. With this design, the pressure ramps up and the load can start softly. This avoids a vibration that can cause noise and increase system load.
Pilot-controlled servo valves are often used in high power applications in industry and aviation. This type of valve has the highest dynamic characteristics among hydraulic valves. There are two types of nozzle baffle and jet tube. Because the torque motor is used to drive the pilot stage [MI], the input electric power is generally very small. But this comes at the cost of the first-stage leakage that always exists when stationary.
A new pilot valve (Figure 2.2.2) has been developed at IFAS to overcome these two current limitations. 1. Improve the dynamic characteristics by using a piezoelectric-bending converter.
2. Avoid leakage at rest by using two independently controllable nozzles.
To improve the piezoelectric-bending transducer, the static force acting on the nozzle is counteracted by a small hydraulic cylinder filled with supply pressure.

Figure 2.2.2 Pilot piezoelectric valve

Under static operating conditions, the two nozzles are almost closed because of the pressure increase in the two piston chambers. This reduces leakage at rest. The spool of the spool valve has been optimized to reduce its mass. Static hydrodynamics are also compensated. The spool displacement is monitored by a small eddy current sensor, which was also developed at IFAS.
Figure 2.2.3 is the step response and frequency response of the valve. It can be seen from the response process that even at 80 input signal strength

It only takes 2 to 3 ms to reach the desired value. The -900 frequency response is about 500 Hz at the input signals 20 and 40, and close to 400 Hz at 80. This prototype test shows that piezoelectric technology has created some new possibilities for fluid technology to break through existing boundaries. This piezoelectric valve was developed for highly dynamic actuators and is used to reduce noise on machine tool active bearings.

Figure 2.2.3 Step response and frequency response of the pilot piezoelectric valve.

Figure 2.2.4 is another example. This is a pilot-controlled cartridge valve with the goal of achieving better performance at low cost [P1]. The valve was developed by Vickers and is called Valvistor (Valve + Transistor). It is based on a flow amplifier with internal pressure feedback and can be single-stage or pilot-controlled. The spool of the cartridge valve and the upper part of the valve sleeve contain
There is a variable orifice for pressure feedback. In order to maintain balance when the pressure drops, the pressure drop at the variable throttle of the two-way valve must be adjusted accordingly. In this way, the desired proportional relationship between the valve opening and the input electrical signal can be achieved. In order to achieve a larger flow rate and better dynamic characteristics, two Valvistors can be connected in series to form a secondary valve, as shown in the lower left corner of Figure 2.2.4. Due to pressure feedback, position sensors are no longer required. For the different deformations shown, the -900 frequency response is around 100Hz. This example shows that the use of low-cost components can also achieve significant improvements in functionality.

Figure 2.2.4 Valvistor Cartridge Valve

2.3 Mechatronics valve
In the industry, a trend in the development of servo valves and proportional valves is the integration of electronic systems and valves. Most of the integrated signal circuits are now composed of digital electronic systems with strong functions, forming decentralized intelligence in the components. The following examples

Introduce this development further.
Figure 2.3.1 is a direct control servo valve [NN1] using linear motor as electro-mechanical converter. Use an LVDT and a pressure sensor to measure position and pressure. The integrated microprocessor and DSP are responsible for all internal data processing. It also handles pressure and position adjustment algorithms. Analog and digital interfaces allow energy input and sensor communication.
It has a special area bus interface, which meets the high-speed requirements of ISO11898, and accepts the CANopen408 format. As shown in Figure 2.3.2, the static and dynamic characteristics of this valve are at least equivalent to those of analog valves.
The advantages of this valve scheme can be summarized as follows:
Valve parameters and magnifications can be changed via the bus, which provides great flexibility and requires very few product types. Have better maintenance possibility and condition monitoring function.
In an environment without a local bus, the valve can also be driven by simulation.

Figure 2.3.1 Sensor integrated direct control servo valve

Figure 2.3.2 Static and dynamic characteristics

The servo valve [NN2] shown in Figure 2.3.3 is another example. The valve contains the second generation digital integrated circuit OBE-D2, which can form an integrated control axis through digital signal processing and regional bus interface. The adjustment algorithms for position, pressure, and synchronization are readily available. As in the previous example, there are a large number of visualization and diagnostic options to control.

Figure 2.3.3 Digital circuit integrated servo valve

Figure 2.3.4 Digital control integrated servo valve

The VNC shown in Figure 2.3.4 has additional integrated numerical control functions and is mainly used in machine tools. Numerical control programs for functional processes can be entered, thus showing the value of decentralized intelligence. The valve is compatible with professional bus-DP and CAN-open.
The last example comes from the hydraulic pressure of walking machinery [K1, W1], Figures 2.3.5 and 2.3.6. The integrated electronic system contained in this valve has most of the functions discussed so far. Because they are used in walking hydraulics, these valves are made into sheets. The valve is used for tractors to comprehensively adjust the displacement and force of the tiller. The lowering movement adopts a single electromagnet plug-in seat valve, and the lifting movement is realized by a pilot solenoid valve which cooperates with the pressure balancing valve.

Figure 2.3.5 Valve with integrated electronic system

Figure 2.3.6 Valve section

2.4 Regional bus format of fluid technology
The purpose of this section is to call attention to efforts to standardize the regional bus format. Some VDMA member companies cooperate with IFAS to develop

A common format is described to describe the functions of the regulating valve, hydraulic pump and intelligent hydraulic drive [B3, NN3].
Figure 2.4 illustrates the system environment of a valve. The fluid technology bus format describes the structure of the instrument, its control and program structure. It also contains some typical adjustment algorithms used in fluid technology. There is also a special section on valves, where the paragraphs describing general functions include the actual values of typical sensors and define the slope format suitable for fluid technology. It is inconvenient to talk too much about details here. Interested readers can read the references in the appendix.

Figure 2.4 Valve system environment-fluid technology bus format

2.5 Unconventional valve scheme
So far, some research and innovations about hydraulic valves have been introduced. They have all been developed in a format that has been tested in practice, or use piezoelectric crystals as electro-mechanical converters.
Figure 2.5.1 shows a brand new structure [F1]. Here an electro-hysteretic liquid is used as the pressure medium. If an electric field is applied, the properties of this liquid will change, and the shear tension of the liquid is proportional to the strength of the electric field, and it appears that the viscosity has changed. This proportional relationship can be used to construct valves without mechanical control edges.
Similar to the servo-hydraulic full-bridge with variable hydraulic resistance [M1], here four hysteresis hydraulic resistances are used, each of which is composed of a ring gap that is easy to manufacture and controlled by a high voltage source . Figure 2.5.2 shows the pressure-flow characteristic curve of the valve with a programmable positive cover of the valve. One advantage of electro-hydraulic valves is that the amount of cover can be changed without changing the hardware.

Figure 2.5.1 Electro-hydraulic servo valve

Figure 2.5.2 Pressure-flow characteristic curve of positive cover

Another advantage of the hysteresis effect is its high dynamic characteristics. Because, because of its working principle, there is little need to push the quality of the dynamic characteristics. A servo hydraulic drive developed and used by IFAS can drive a loudspeaker and play a CD of music, which proves this point.

3. Pneumatic valve
The demand for automation technology has driven the development of pneumatic valves. Pneumatics has become the engine driving fluid technology innovation. The trend of miniaturization, improvement of dynamic characteristics, application of piezoelectric technology and application of regional bus technology are obviously earlier in pneumatics than in hydraulics. A new trend in valve development is focused on micropower, microvalves using silicon etching technology. Since the application of pulse width modulation (PWM) control can achieve almost continuously adjustable power characteristics, this chapter will also introduce fast pneumatic valves.

3.1 Valve miniaturization
As already mentioned, there is a strong demand for small valves in the market, and all major manufacturers have recently responded with corresponding R & D. One technical solution may lie in miniaturizing conventional electric drives. Figure 3.1.1 is the first example, showing a valve used in the electronics and mechatronics industry. This is a plug-type valve for board mounting. Its flow rate is 10NL / min, used in the semiconductor manufacturing industry.

Figure 3.1.1 Direct control of small valves

Figure 3.1.2 Quick switching valve

The demand for miniaturization is linked to improved dynamic characteristics. Figure 3.1.2 shows two pilot-controlled valves. The valve on the integrated island shown in the upper left corner of the figure has a flow rate of 100NL / m and a switching time of 2 ~ 6ms. The pilot valve shown on the right is also a four-fold flow rate with a switching time of 6ms. The electrical power required depends on the switching time. When the switching time is 6ms, both are about 3w.
Figure 3.1.3 shows some other examples of unconventional designs [F2]. They avoid the disadvantages of many miniaturized valves: the elastic seal is mounted on the armature, thus limiting the effective range of the armature.

Figure 3.1.3 Direct control of the dynamic characteristics of small valves

The upper part of the figure shows a cross-sectional view of different structures. Their dynamic characteristics can be evaluated based on the step response shown at the bottom of the figure. The vane valve is a pulse valve with a permanent magnet incorporated in the switching circuit to generate a pre-tightening force. An elastic frame mounted between the housings completely separates the fluid part from the electro-mechanical drive part. The standard diameter of all valves is 0.6mm, and the flow of the vane valve is 7.5NL / m. The electric power is 1 to 1.5w.

3.2 Integration of electronic components
Similar to that described in the hydraulic proportional valve, the trend of integration of digital electronic technology can also be seen in the development of pneumatic valves. Figure 3.2.1 shows two examples: the pressure regulating valve is on the left. On the right is a three-position five-way proportional directional valve. The pressure regulating valve has a pressure sensor, the maximum flow rate is 120L / min, and the electric power consumption is 2w. The three-position five-way proportional valve is a direct-acting type with a flow rate of 1000 to 4000 L / min.

Figure 3.2.1 Valve integrated with digital electronic technology

They can have a regional bus interface. The parameters can be adjusted via the attached keys and display or via a PC connected to it, so it can be adjusted both offline and online. This flexible interface further ensures diagnostic and condition monitoring functions.

Figure 3.2.2 Valve with condition monitoring function

Figure 3.2.2 is an example of digital electronic technology integration and condition monitoring functions. For automation and digital control, the bus module-valve unit is connected to the regional bus. Other valve units and input-output modules are connected to independent branches of the bus system. This diagnostic function can be extended to the level of the valve and the coil. The input level, transmission and construction errors can be identified at the system level. At the valve level, voltage fluctuations or input and output errors (short circuit, open circuit) can be identified.
For valves with feedback functions, such as pressure regulators, an impermissible deviation will cause an error report. In this way, errors can be accurately determined, so that components can be replaced quickly or stopped.

3.3 Using modulation to achieve continuously adjustable power characteristics
Thanks to the high compressibility of air, it is possible to use an on-off valve to achieve a nearly continuously adjustable working process. A typical example of adjustment is pulse width modulation, where the amplitude and maximum period are kept constant. Pulse width modulation from Tmin to Tmax, Tmin depends on the sampling frequency and the dynamic characteristics of the valve.

Figure 3.3.1 Mass flow modulation with high control frequency and voltage amplitude

Research was conducted at IFAS to improve this current technology’s adjustment algorithm [C1]. To this end, the control frequency is increased beyond what is defined for fully opening the valve. At this time, the valve displacement can be affected by the amplitude of the added voltage, because the pulling speed of the magnetic field depends largely on the input voltage.
Figure 3.3.1 shows the final effect.
When the input signal is 150 to 250 valve rated control voltage, almost linear characteristics can be obtained. Another possibility of flow modulation can be obtained by using different pulse patterns and control frequencies.
Figure 3.3.2 illustrates the control
The relationship between the signal and the spool displacement at high and low frequencies. At low frequencies, pulse modes 1100 and 1010 both cause the valve to fully open. However, after switching to high frequency, the valve can be fully opened in pulse mode 1100, and mode 1010 causes only a partial displacement of the spool.

Figure 3.3.2 Pulse mode and valve characteristics

Figure 3.3.3 Flow linearization results

This pulse mode deformation (PWV) can be combined with pulse amplitude modulation (PAM). Figure 3.3.3 shows the comparison with pulse width modulation (PWM). The same valve and the same control frequency are used here. The pressure is 4 bar. For comparison, the results of time-discrete PWM are also drawn at the same time. This example illustrates the potential of additional intelligence in control algorithms. Ignoring the effect of the pressure level on the rise and fall of the flow rate, changing the pressure of the gas source ± 2 bar has no effect on the linearization characteristics.

3.4 Low power consumption valve

Figure 3.4.1 Schematic diagram of piezoelectric driven low power consumption valve

Figure 3.4.2 Piezo-driven low power valve internal structure

If the energy supply of the valve comes only from the local bus or the self-insurance current loop, it is important to reduce the power consumption of the valve. The most suitable for this requirement is the piezoelectric actuator. As already mentioned, it consumes almost no energy when stopped in a position. Because the force requirements in pneumatics are much lower than in high-pressure hydraulic systems, piezoelectric-bending transducers can be used, which can provide greater displacement than piezoelectric-stack actuators. Figure 3.4.1 is a schematic diagram of the structure of a low power consumption valve [V1] that is currently available on the market. This is a two-position three-way valve. If the nozzle and the control circuit are slightly modified, it can be used as a switching valve or a proportional valve. The lower part of the figure is its characteristic curve. Considering its working pressure range, it is used as a pilot valve. The switching time is less than 2ms, and the switching energy is only 0.014 milliwatts. The valve has a diameter of 0.33mm and a rated flow rate of 1.5NL / min.
Figure 3.4.2 can help to understand the internal structure of the product, understand the component size and tolerance required by the technology.

Figure 3.4.3 Low power piezoelectric valve

Figure 3.4.3 shows another valve using a piezoelectric bending transducer. The valve is larger with a maximum flow of 3L / min and a pressure of 7 bar. The electric power consumption is 0.11w, and the switching time is 55 to 85ms.
The right part of the figure is the dynamic characteristics. The valve can also be used as a proportional valve. It can also be installed on a main stage with double membranes.
The last example of a low power valve is currently being developed by IFAS [B4]. The valve can work in a pneumatic network with full pressure. Figure 3.4.4 is a schematic diagram of the valve structure. The piezoelectric bending converter is vertically installed on the spool of the cubic slide valve which can move up and down. This part has a hose connected to the air source. A lateral hole and a hole communicating with cavity A and cavity B respectively form two control edges. Because the valve is closed in the neutral position, the median leakage is very low.
The rated flow of the valve is 6NL / min, and the electrical power consumption depends on the operating frequency of the valve and the control circuit used. Static consumption is almost zero. Figure 3.4.5 shows the frequency response at 8 bar, with input signal levels of 20, 50 and 100, respectively. Even at 100 signals, the phase shift of -900 exceeds 100 Hz. This shows that this low-power valve has high dynamic characteristics.

Figure 3.4.4 Low power piezoelectric valve

Figure 3.4.5 Control characteristics

3.5 Mini valve
With the advancement of silicon etching technology, it is now possible to form a three-dimensional structure. In this way, nozzles and similar elements can be constructed. In this way, the experience and invention accumulated in the semiconductor industry can be used to develop and produce microstructures. There are many lessons that can be learned from the electronic components of vehicles, such as acceleration and pressure sensors. So far, due to the limitation of material strength, it can only be used to control low pressure, such as in pneumatic systems.
The following describes two examples of actuators driven by different physical principles. Figure 3.5.1 is the first example, applying electrostatic drive.

Figure 3.5.1 Electrostatically driven microvalve

Figure 3.5.2 Mini valve with main valve and electronic circuit

This valve has a three-way function. The valve body is switched after voltage is applied, so that the working chamber is connected with the pressure chamber or the return chamber. The spool is spring-centered and can be stopped in various positions. Does not consume energy. From the perspective of electronic technology, it is like a capacitor. Based on physical principles, its displacement is limited to 5 microns. The diameter is 0.2 and the flow is 0.3NL / min. This small flow drives a main stage and is also pneumatic. The diameter is 1.7 and the flow can reach 80NL / min.
Figure 3.5.2 is a picture of this valve with main valve and electronic circuit, its size can be seen. The picture on the right is a microvalve mounted on a ceramic base. The background is a whole microvalve silicon wafer.

Figure 3.5.3 Heat-driven microvalve

Figure 3.5.4 Dynamic characteristics of the thermal push valve

The second example is a thermally driven microvalve. This was jointly developed by IFAS and the Institute of Silicon Technology of the Academy of Applied Sciences. Figure 3.5.3 shows its internal structure and applied process. A pre-tensioned nickel bridge is heated, which stretches and bends, closing or opening a nozzle. Based on this principle of action, this valve requires at least one watt of power input to control a pressure of 10 bar. This valve can be designed as a two-position two-way, or two-position three-way proportional valve. The advantage of this valve is the large displacement, up to 40 microns. Although the valve is thermally driven, it still exhibits excellent dynamic characteristics as shown in Figure 3.5.4. The step response time is 16ms. Due to the large displacement of the valve core, the maximum flow rate of the valve is an order of magnitude higher than that of the electrostatic valve.

3.6 Micro-module connection

Figure 3.6.1 An example of an integrated microsystem

As mentioned earlier, the initial R & D and production of micro-systems were for high-volume applications, mainly in the automotive industry. Due to the quantity required by the customer, the special design meets the corresponding market demand. Looking at other markets, the situation is different. Since the machine manufacturing industry other than the automobile industry has insufficient demand for sensors and valves, it is not enough for the design of customer-specific machine and electronic units. Therefore, the idea of ​​providing a module or building block system to meet the requirements of the electromechanical subsystem [S1]. Fig
3.6.1 shows an example of a pressure sensor. A standardized housing and standardized interface are used, but only the components corresponding to the requirements are housed in the housing. In this example, it is a pressure sensor, a temperature sensor, a signal converter, a program and data information storage, a bus interface, all these components together form an intelligent pressure temperature sensor.
This standardization was jointly developed by the IPA, IZM Institute and VDMA of the Academy of Applied Sciences. They proposed a solution for the interfaces needed to connect different technologies such as electronics, machinery and fluids. Figure 3.6.2 shows a bus scheme, which can connect micro-modules into a structural system. This system consists of, for example, optical, jet and electronic systems. Special bus connection components to transmit energy and signals. A group of experts from VDMA member companies participated in the project and helped define the interface and connection.

Figure 3.6.2 Bus solution for connecting micro modules

4. Summary
Although there is a tendency to use more pump adjustment, fixed displacement pumps through displacement adjustment or speed adjustment, to control hydraulic power, the valve is always the heart of today’s hydraulic system, which is also applicable to pneumatics. In order to adjust the variable mechanism of the pump and the motor, the valve is indispensable, but at this time it works in the control loop. It can also be used directly in the main circuit to control flow and pressure. Proportional valves and fast switching valves with intelligent control algorithms represent electro-fluid converters. Competing with electrical and mechanical transmissions worldwide means that the potential of fluid technology must be constantly tapped.
Examine the examples given to introduce innovations in the structure and control edges of proportional valves, and you will know how widely the solutions are distributed. By improving the traditional structure, inserting new components can also achieve many effects. But the biggest innovation is to integrate more intelligence into the valve and drive electronics system, and to communicate with the surrounding environment of the valve, decentralized intelligence with additional computing power, used for diagnosis, and integrated into the control loop, has become the current technical level Provide users with new possibilities.
New materials, such as piezoelectric ceramics, hysteresis fluids, and new manufacturing processes, such as silicon etching technology, provide soil for new solutions. The fluid technology industry and high calibration are actively taking new paths to enhance the competitiveness of fluid technology.

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