Do you know pneumatic valve positioners? Pneumatic valve positioners are one of the most important accessories and accessories for pneumatic control valves. The role of valve positioning. Pneumatic valve positioners and pneumatic actuators together form a self-controlled unit and a variety of regulating valve connections. After commissioning and installation, they are combined into a pneumatic regulating valve. Used in various industrial automation process control areas. The following Xiaobian introduced relevant knowledge about pneumatic valve positioners for everyone. Let's learn about it together.
Pneumatic valve positioner working principle
Pneumatic valve positioner works according to the principle of moment balance. When the signal pressure P1 passing through the bellows 2 increases, the main lever 3 rotates around the fulcrum, so that the nozzle baffle 9 approaches the nozzle, and the nozzle back pressure is amplified by the one-way amplifier 8. After that, the pressure to the membrane chamber of the actuator increases, causing the valve stem to move downwards. The feedback lever rotates around the fulcrum, and the feedback cam also rotates counterclockwise. The auxiliary lever 4 is rotated around the fulcrum by the roller, and the feedback spring is stretched. The tension and signal pressure of the spring on the main lever 3 are used in the bellows. When the force reaches equilibrium, the meter reaches equilibrium. The valve position of the actuator is maintained at a certain opening, and a certain signal pressure corresponds to a certain valve position opening. The above action mode is a positive action. If you want to change the action mode, just flip the cam and turn A into B direction. The so-called positive acting positioner means that the signal pressure increases and the output pressure increases. The so-called reaction positioner increases the signal pressure and decreases the output pressure. If a positive acting actuator is equipped with a reaction locator, it can achieve the action of the reaction actuator. Conversely, if a reaction actuator is equipped with a reaction locator, the positive actuator can be actuated.
Pneumatic valve positioner structure principle
Pneumatic valve positioner receives weak signal from 4-20mA in controller or control system, and sends air signal to pneumatic actuator to control valve position.
It is used with a pneumatic control valve to form a closed loop control loop. The DC current signal given by the control system is converted into a gas signal that drives the regulating valve to control the operation of the regulating valve. At the same time, feedback is made according to the opening degree of the regulating valve, so that the valve position can be correctly positioned according to the control signal output by the system.
Pneumatic valve positioner features
Pneumatic valve positioner has many characteristics. Its structure is equipped with a large-caliber pilot-type relay device. This relay device can well prevent blockage of the air circuit, so that the action of the regulating valve will be quickened. This locator is relatively sensitive, so it can be used very well in changes in working conditions, can be adjusted in a timely manner, and continue to work in a stable manner. If you need to change the working mode during the work process, you do not need to change the part. You only need to adjust the specific installation position of the relay in the positioner.
This type of valve positioner is not very demanding for its partner, that is, the pneumatic control valve, and can be within various pressure ranges. Pneumatic valve positioners can perform split-range control. The positioner signal range is not all but a part of the entire control signal, so if there is a control signal, it can control multiple positioners well.
Pneumatic valve positioner is a relatively important part, so it will be used in many places, if you want to purchase, we must pay attention to the following aspects: whether the positioner can achieve a split, whether it can be easier to zero and Adjustment of the range, how the stability of the first two, precision can reach what extent and so on.
The above is a brief introduction for Xiaobian. If you want to know more related information, please continue to pay attention to Qijia Consulting. More exciting consultation, please stay tuned.
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