Difference between valve positioner and actuator

The valve positioner is the main accessory of the regulating valve and is used in conjunction with the pneumatic regulating valve. It accepts the output signal of the regulator and then uses its output signal to control the pneumatic regulating valve. When the regulating valve is actuated, the displacement of the valve stem passes through the mechanical The device feeds back to the valve positioner. The status of the valve position is transmitted to the upper system by electrical signals.

According to its structure and working principle, the valve positioner can be divided into pneumatic valve positioner, electro-pneumatic valve positioner and intelligent valve positioner.

The valve positioner can increase the output power of the regulating valve, reduce the delay of the transmission of the adjustment signal to the valve positioner, speed up the movement speed of the valve stem, can improve the linearity of the valve, overcome the friction of the valve stem and eliminate the influence of unbalanced force, In order to ensure the correct positioning of the regulating valve.

Commonly used actuators: Pneumatic actuators, electric actuators, straight stroke, angular stroke points. For automatic, manual opening and closing all types of cutting doors, wind panels and so on.

The use of positioners in the control of the valve positioner enables high-quality adjustments and increases the accuracy and stability of the process control. The regulating valve is the terminal of the control system. Once it fails, it will directly affect the safe operation of the device and has a great impact on the production process.

The use of a smart valve positioner can improve the flow characteristics and performance of the regulating valve. It can provide digital information communication with DCS or bus equipment to provide safe and stable production of the device.

1. The disadvantages of the conventional positioner are as follows: 1) Conventional positioners are mostly based on the principle of mechanical force balance. It adopts a nozzle flapper mechanism, which has many movable parts and is easily affected by disturbances such as temperature fluctuations and external vibrations. It is also poor in environmental resistance; the elasticity of springs The coefficient can change under the bad environment, will cause the non-linearity of the control valve, cause the control quality to decline; The outside vibration is transmitted to the force balance mechanism, can cause the component to wear out and zero point and journey to drift, make the positioner difficult to work too;

2) due to the characteristics of the nozzle itself, the actuator must consume a large number of regulators to reduce the air moving valve in the steady state, if the use of a large number of actuators, energy consumption; and the nozzle itself is a potential regulator valve source, Easy to be blocked by dust or dirt particles, making the locator not work properly;

3) Conventional valve positioners need to use special equipment to manually adjust valve timing. It is not possible to isolate the control loop. Zero point and stroke adjustment influence each other. The entire positioner must be repeated, time-consuming and labor-intensive. Difficult to adjust.

The performance of the intelligent electric valve positioner has made a big leap compared with the traditional valve positioner. The intelligent electric valve positioner has higher positioning accuracy, wider application range, and more convenient and reliable use. But in the specific valve, it is reasonable to meet the safety requirements, better control effects, matching with the control loop, adapting to special environmental requirements, and prolonging the service life. Regulator positioner type, and its valve parameter settings and adjustments.