Control valve petrochemical automation 2003, 394 control valve pneumatic film actuator output force and its performance improvement 裘樟樵 China Tianchen Chemical Engineering Company, Tianjin 3004001 theoretical lag For a long time, the domestic interpretation of the output force of pneumatic film actuator is not clear, It is difficult to understand or even erroneous, so that the use of air pressure energy of pneumatic control valves in the manufacturing process and in actual use is wrong. Foreign advanced manufacturers control valve pneumatic pressure up to 700kPa, while domestic manufacturers still use 140kP in large quantities, a few are 300kPa. Chemical automation is developed from pneumatic instruments, pneumatic control valves from pneumatic transmitters pneumatic control valves, all using 20100kPa air pressure transmission signal. At the beginning, without a valve positioner, the valve was directly pushed with a pressure of 20100 kPa, and the transmitted signal was used as a power signal. This signal is sufficient for the transmitter and regulator energy, but the control valve is obviously not strict enough, can not be opened, slow motion, bulky, or the positioner is only used as flow amplification, but the pressure is still 20100kP, only Achieve partial reduction of lag. This is very unreasonable, and the transmission of signals as a power signal is a theoretical lag and misleading.
2 Mechanical analysis of pneumatic membrane actuators The following is an example of a gas shutoff valve with a gas supply pressure of 600 kPa. Detailed 1.
Within the range, the actuator stem displacement is 0. The spool is at the full-opening plenum supply pressure; the relative stroke spring stroke is compressed downward from 150 kPa, the pressure rises to 300 kPa, and the full stroke spool reaches the fully closed position. When the spool is held by the valve seat, the theoretical clearance is zero and cannot be moved down. However, when the reaction force of the process medium causes the spool to move upward, the valve positioner changes the nozzle balance end position. The output air pressure continues to increase. Its output pressure varies within a range of 300, causing it to return to its position. The maximum supply pressure reaches 600kPa.300, the pressure of 600kPa is after the aerodynamic thrust overcomes the spring balance force, including the date of the release date 2002, the date of the revised manuscript 20021209, the automation department of the Chemical Engineering Department of Jiang University, Benedictine is now working at Tianchen Chemical Engineering Co., Ltd. The engineer is the chief engineer, and the direction of the automatic control valve and valve has been discussed. The force that can be increased by rubbing gravity has been called the output force. There is information that superbalance is more appropriate. It also has the same effect in the middle of the stroke. That is, the reaction force changes the stroke position, and the output pressure increases to return it to its original position.
The magnitude of the output force determines the size of the differential pressure allowed by the valve body. This force is purely supplemented by the action of the positioner after overcoming the balance force of the spring. It is the importance of specifically counteracting the reaction force of the fluid. Because the valve body is always present, sometimes even large, such as the vent valve relief valve. If there is no positioner, there is no output force shut-off valve, and the gas shut-off valve without the positioner can not be closed, and the water is far away. Always there. If there is no locator output force, the thrust and spring reaction force reach a certain balance at a certain position, and the thrust is equal to the balance force and stops at a certain position. If it is in the fully closed position, when the reaction force increases, the spool will inevitably go up. This displacement is proportional to the magnitude of the reaction force, the reaction force is large, the upward displacement is large, the reaction force is small, and the displacement is small. Regardless of the displacement fire is also small, called the core away from the position. The greater the reaction, the greater the leakage inside the valve, and vice versa. The valve is always leaking, because the medium always has a reaction force, but the size of the leak is asked.
If it is in the middle position, the signal does not correspond to the displacement.
For the gas-opening valve, the initial pressure of the spring can be used as the output force, but the pressure of 201 kg 3 is too small, the force is not enough, and the ability to overcome the differential pressure of the medium is limited. You must try to increase the starting pressure. You can move the elastic range to the right, 1.
The working principle of the locator is detailed 2.
The input signal rises, so that the baffle is close to the nozzle, so that the back pressure is raised, the output of the output is raised by the pneumatic amplifier, and the valve stem drives the baffle downward to form a negative feedback. When the input signal is balanced with the feedback, the spool is at a certain opening degree, the baffle is in equilibrium, the output factory is stable at a certain value, and the valve is at a fixed opening degree.
If the reaction force of the medium rises, the valve stem is pushed up, and the downward force of the feedback force 5 is reduced, so that the left side of the baffle is upward, and the reaction force of the medium is entered on the right side of the baffle. Return the spool to its original position. In actual use, the thrust and the reaction force are simultaneously performed simultaneously.
The media reaction force rises, that is, the negative feedback force decreases, that is, positive feedback, and the positive feedback is approximated by the lag and spring hysteresis. That is, the positioner can eliminate the positional deviation. 3 Conclusions and improvements can be seen from the above analysis.
The spring diaphragm actuator has an output force when the valve positioner has a valve. The starting range of the valve is the output force and no output force.
The valve is never closed.
The greater the supply pressure, the greater the output force that can be accommodated, the greater the reaction force can be overcome, and the larger size valve can be driven. Straighten to the supply pressure and overcome the greater the elastic range of the spring. The stiffness has an effect on the reaction force changing stroke. The greater the stiffness, the smaller the reaction force changes to the stroke, and vice versa. However, the stroke change can never be used without a valve positioner. As can be seen from 1, the spring elasticity range is 0 size valve, gas clearance and different stiffness requirements. The greater the gas supply, the greater the choice. Shifting to the right increases the output of the gas opening. The halving shift increases the output force of the igniter valve. , 015, is the spring starting pressure, and the gas supply pressure of the helium valve is increased, and the same thrust and output force can be obtained under the condition of reducing the diaphragm size, thereby achieving miniaturization of the actuator. In order to achieve a truly fine structure.
The greater the thrust, the greater the friction of the stem and the larger the stem diameter. The better the stability.
The stem packing is pressed tightly to make the stem leak less, allowing for greater friction. Therefore friction is not a negligible force. Direct relationship to extracorporeal leakage. Previously, the often negligible reference to the data was small and correct.
The gas supply pressure is increased, and a wide range of springs can be used to make the valve work more stably. Reduce vibration and noise, and increase the linearity of the yellow, that is, use the linear part of the spring.
The gas supply pressure is increased, which can increase the operating speed of the valve and reduce the system lag. Add atmospheric flow if necessary. For example, pneumatic pipelines use 饨, 10, and 12, etc.
Rat. The application technology of the unit shafting instrument discusses the cost of the parts and transmitters.
Although this application has been implemented on the plant's multi-food device. However, there have been problems in the application process. The following is applied, for a brief introduction, to provide you with reference.
First of all, this application was realized on the main fan unit of the 34 catalytic device of the plant, and the application was good. The system has been operating normally since 1998. After the first application, the plant adopted a sample plan for the modification of the 24 catalyzed gas jade unit control system.
Signal oscillation occurred after installation and operation. After many analysis and processing, there is still no solution. After the 24 power supply is replaced, the signal is normal. Thanks to technical support for the first application.
The author only suspects that there is a question about the quality of the product. And did not play in the technical depth 1 to go, the first time. In the process of 1 catalytic hood renovation. The same signal oscillation occurred, and the system was normal after replacing the power supply. then. The author has to provide 24 DC power to the system in the technology 1 and the sensor part of the transmitter and Betltly, and the front-end device such as 1 is a high-frequency oscillation source. Therefore, the source of signal oscillation can only be a DC power supply or a mismatch between the transmitter and the preamplifier. The success of 3+ catalysis should be different between the transmitter and the preamplifier. Then, the biggest possibility is the quality of the DC power supply. To this end, DC power supplies with different results before and after were tested. The test found that the original power supply has an AC component of about 3, and the AC component of the power supply after replacement is also about 261. Then analyze their AC distribution waveforms. Obtain the original source AC component waveforms 1 and 2.
After the replacement, the AC component waveforms 3 and 4 of the power supply do not.
3 AC component waveform of the power supply after replacement 1 4 AC component waveform of the power supply after replacement 2 As can be seen from the waveform, the quality of the DC power supply after replacement is not better or even worse than the original power supply. However, the power supply after the replacement of the electric shock pulse of the left and right at the relatively low frequency is large, but the waveform is uniform and the frequency is high.
The interference affecting the output of the 1 heart transmitter is obviously that the comparison of the low frequency band keys from 1 and 3 also shows that the AC component pulse of the original power source is basically in the positive direction. After the history change, the symmetry of the AC component in the positive and negative direction is better. This may be the location of the original power supply, indicating that the average value of the power supply disturbance may also affect the transmitter output. Through the above analysis, the author Have a deeper understanding of the performance of the transmitter! I know some technical problems that are easy to neglect when I am using the transmitter. I also hope that the manufacturer can attract attention and improve it.
3 Conclusion If you want to be compatible with different products, you will definitely encounter more technical questions. In the current fierce commercial competition environment, all manufacturers pay special attention to technical secrecy, and at the same time try their best to realize profits and humanization. therefore. It is bound to affect the user's product application in a small amount, as the user can only study technology and boldly try to achieve technical and economic optimization.
As the company's cost reduction and efficiency work is carried out, it is necessary to ensure system investment, which raises higher requirements. By optimizing the instrument configuration to reduce investment, this work is promising.
This is a waste of energy, which is the reason why the pressure of foreign gas supply can reach 70013.
In order to increase the supply pressure, the membrane chamber structure must be improved, including the diaphragm material and spring properties as well as the membrane chamber seal.
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