Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question from 2020-09-10

1. Improve the static characteristics of the control valve and enhance the linearity of the valve position. 2. Improve the dynamic characteristics of the control valve and reduce the transmission lag of the control signal. 3. Change the flow characteristic of the control valve. 4. Change the response range of the control valve to the signal pressure to achieve step control. 5. It is possible to reverse the valve’s operation.

1. Improve the static characteristics of the control valve and enhance the linearity of the valve position. 2. Improve the dynamic characteristics of the control valve and reduce the transmission lag of the control signal. 3. Change the flow characteristic of the control valve. 4. Change the response range of the control valve to the signal pressure to achieve step control. 5. It is possible to reverse the valve’s operation.

Functions of a valve positioner: 1. Improving the steady-state characteristics of the valve. With the use of a valve positioner, even minor changes in the controller’s output signal can result in significant variations in the air pressure supplied to the diaphragm of the control valve. This allows for overcoming the friction associated with the valve stem and eliminating the effects of unbalanced forces on the control valve, thereby ensuring that the valve is positioned accurately according to the signals sent by the controller. After improving the steady-state characteristics, the control valve can be used in the following situations: ① Cases where adjustment of the valve position is required ； ②Applications with large diameters, high pressure differences, and other conditions resulting in significant unbalanced forces ； ③To prevent leakage, it is necessary to compress the stuffing box tightly, such as in situations involving high pressure, high temperature, or low temperature ； ④There are solid particles stuck in the process medium, or the viscosity is high. 2. Improving the dynamic characteristics of the valve: The actuator alters the original first-order lag characteristic of the valve, reduces the time constant, and turns it into a proportional characteristic. Generally speaking, when the pressure transmission pipeline exceeds 60 m, a valve positioner should be used. 3. Changing the flow characteristics of the valve: By altering the shape of the actuator feedback cam, it is possible to switch between linear, logarithmic, and fast-opening flow characteristics for the control valve. 4. For proportional control, one controller is used to operate two or more control valves, enabling them to complete a full stroke of movement within a certain range of the signal. For example, make the two control valves complete a full stroke of movement within signal ranges of 4–12 mA DC current and 12–20 mA DC current, respectively. 5. Valve positioners used for the reverse operation of valves come in positive and negative acting types. During positive action, as the input signal increases, the output air pressure also increases ； During reaction, the input signal increases while the output air pressure decreases. Using a reverse-action locator can convert a air-operated open valve into an air-operated closed valve, and vice versa.

1. To improve the steady-state characteristics of the valve, by using a valve positioner 5261, even a slight change in the output signal from the controller 4102 can, through the nozzle-and-baffle system along with the amplifier, cause a significant change in the air pressure acting on the diaphragm of the control valve. This helps to overcome friction in the valve stem and eliminate the effects of unbalanced forces on the control valve, thereby ensuring that the valve is positioned accurately according to the signals sent by the controller. After improving the steady-state characteristics, the control valve can be used in the following situations: ① Cases where adjustment of the valve position is required ； ②Applications with large diameters, high pressure differences, and other conditions resulting in significant unbalanced forces ； ③To prevent leakage, it is necessary to compress the stuffing box tightly, such as in situations involving high pressure, high temperature, or low temperature ； ④There are solid particles stuck in the process medium, or the viscosity is high. 2. Improving the dynamic characteristics of the valve: The actuator alters the original first-order lag characteristic of the valve, reduces the time constant, and turns it into a proportional characteristic. Generally speaking, when the pressure transmission pipeline exceeds 60 m, a valve positioner should be used. 3. Changing the flow characteristics of the valve: By altering the shape of the actuator feedback cam, it is possible to switch between linear, logarithmic, and fast-opening flow characteristics for the control valve. 4. For proportional control, one controller is used to operate two or more control valves, enabling them to complete a full stroke of movement within a certain range of the signal. For example, make the two control valves complete a full stroke of movement within signal ranges of 4–12 mA DC current and 12–20 mA DC current, respectively. 5. Valve positioners used for the reverse operation of valves come in positive and negative acting types. During positive action, as the input signal increases, the output air pressure also increases ； During reaction, the input signal increases while the output air pressure decreases. Using a reverse-action locator can convert a air-operated open valve into an air-operated closed valve, and vice versa.

Functions of a valve positioner: 1. Improving the steady-state characteristics of the valve. By using a valve positioner, even slight changes in the signal output by the controller can result in significant variations in the air pressure supplied to the diaphragm of the control valve. This helps to overcome friction in the valve stem and eliminate the effects of unbalanced forces on the control valve, thereby ensuring that the valve is positioned accurately according to the signals sent by the controller. After improving the steady-state characteristics, the control valve can be used in the following situations: ① Cases where adjustment of the valve position is required ； ②Applications with large diameters, high pressure differences, and other conditions resulting in significant unbalanced forces ； ③To prevent leakage, it is necessary to compress the stuffing box tightly, such as in situations involving high pressure, high temperature, or low temperature ； ④There are solid particles stuck in the process medium, or the viscosity is high. 2. Improving the dynamic characteristics of the valve: The actuator alters the original first-order lag characteristic of the valve, reduces the time constant, and turns it into a proportional characteristic. Generally speaking, when the pressure transmission pipeline exceeds 60 m, a valve positioner should be used. 3. Changing the flow characteristics of the valve: By altering the shape of the actuator feedback cam, it is possible to switch between linear, logarithmic, and fast-opening flow characteristics for the control valve. 4. For proportional control, one controller is used to operate two or more control valves, enabling them to complete a full stroke of movement within a certain range of the signal. For example, make the two control valves complete a full stroke of movement within signal ranges of 4–12 mA DC current and 12–20 mA DC current, respectively. 5. Valve positioners used for the reverse operation of valves come in positive and negative acting types. During positive action, as the input signal increases, the output air pressure also increases ； During reaction, the input signal increases while the output air pressure decreases. Using a reverse-action locator can convert a air-operated open valve into an air-operated closed valve, and vice versa.

1. Improve the static characteristics of the control valve and enhance the linearity of the valve position. 2. Improve the dynamic characteristics of the control valve and reduce the transmission lag of the control signal. 3. Change the flow characteristic of the control valve. 4. Change the response range of the control valve to the signal pressure to achieve step control. 5. It is possible to reverse the valve’s operation.

1. Improve the static characteristics of the control valve and enhance the linearity of the valve position. 2. Improve the dynamic characteristics of the control valve and reduce the transmission lag of the control signal. 3. Change the flow characteristic of the control valve. 4. Change the response range of the control valve to the signal pressure to achieve step control. 5. It is possible to reverse the valve’s operation.

Function of the valve positioner: 1. Improving the steady-state characteristics of the valve. With the use of a valve positioner, even minor changes in the signal output by the controller can result in significant variations in the air pressure supplied to the diaphragm of the control valve. This helps to overcome friction in the valve stem and eliminate the effects of unbalanced forces on the control valve, thereby ensuring that the valve is positioned accurately according to the signals sent by the controller. After improving the steady-state characteristics, the control valve can be used in the following situations: ① Cases where adjustment of the valve position is required ； ②Applications with large diameters, high pressure differences, and other conditions resulting in significant unbalanced forces ； ③To prevent leakage, it is necessary to compress the stuffing box tightly, such as in situations involving high pressure, high temperature, or low temperature ； ④There are solid particles stuck in the process medium, or the viscosity is high. 2. Improving the dynamic characteristics of the valve: The actuator alters the original first-order lag characteristic of the valve, reduces the time constant, and turns it into a proportional characteristic. Generally speaking, when the pressure transmission pipeline exceeds 60 m, a valve positioner should be used. 3. Changing the flow characteristics of the valve: By altering the shape of the actuator feedback cam, it is possible to switch between linear, logarithmic, and fast-opening flow characteristics for the control valve. 4. For proportional control, one controller is used to operate two or more control valves, enabling them to complete a full stroke of movement within a certain range of the signal. For example, make the two control valves complete a full stroke of movement within signal ranges of 4–12 mA DC current and 12–20 mA DC current, respectively. 5. Valve positioners used for the reverse operation of valves come in positive and negative acting types. During positive action, as the input signal increases, the output air pressure also increases ； During reaction, the input signal increases while the output air pressure decreases. Using a reverse-action locator can convert a air-operated open valve into an air-operated closed valve, and vice versa.

1. Improve the static characteristics of the control valve and enhance the linearity of the valve position.     2. Improve the dynamic characteristics of the control valve and reduce the transmission lag of the control signal.     3. Change the flow characteristic of the control valve.     4. Change the response range of the control valve to the signal pressure to achieve step control.     5. Reverse the valve operation.  

1. Improve the static characteristics of the control valve and enhance the linearity of the valve position. 2. Improve the dynamic characteristics of the control valve and reduce the transmission lag of the control signal. 3. Change the flow characteristic of the control valve. 4. Change the response range of the control valve to the signal pressure to achieve step control. 5. It is possible to reverse the valve’s operation.