Instruments: [Weekly Question] Week 38 of 2011: What are the functions of valve positioners?

This post was last edited by denghl on 2012-12-1 at 18:02 to 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.

This post was last edited by denghl on 2012-12-1 18:02 (1) It is used in important control systems where high requirements are placed on control quality, in order to improve the positioning accuracy and reliability of control valves. 　　 (2) Used in applications where the pressure difference across the valve is high (△p>1MPa). By increasing the gas supply pressure to boost the output force of the actuator, it is possible to overcome the unbalanced force exerted by the liquid on the valve spool and reduce stroke error. 　　 (3) When the medium being handled is at high temperature, high pressure, low temperature, or is toxic, flammable, or explosive, in order to prevent external leakage, the packing is often compressed tightly; as a result, the friction between the valve stem and the packing is high. In such cases, a positioner can be used to overcome the time delay. 　　 (4) When the medium being regulated is a viscous fluid or contains solid suspensions, a positioner can overcome the resistance exerted by the medium on the movement of the valve stem. 　　 (5) Used in control valves with large diameters (Dg>100mm) to increase the output thrust of the actuator. 　　 (6) When the distance between the regulator and the actuator is over 60 m, a positioner can overcome the delay in the transmission of control signals, thereby improving the response speed of the valve. 　　 (7) Used to improve the flow characteristics of control valves. 　　 (8) When a regulator controls two actuators for step control, two positioners can be used to receive the low and high input signals respectively; thus one actuator operates at the low level while the other operates at the high level, thereby achieving step regulation.

This post was last edited by denghl on 2012-12-1 at 18:02. Reply 1#: The main functions of the valve positioner in Baghdad are as follows: 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.

This post was last edited by denghl on 2012-12-1 at 18:03. 1. It is used to increase output capacity, and is mainly applicable in situations involving high pressure differences, high-pressure media, high temperatures, low temperatures, and large-diameter valves. 2. It is used to improve the quality and operating speed of control valves, primarily due to the presence of an amplifier and sufficient air supply pressure. 3. Used for electro-pneumatic conversion; currently, most control valves are used in conjunction with computers, and the output from computers is usually a 4–20mA current signal. Electro-pneumatic valve positioners can be used to meet these requirements. 4. Used for stepwise regulation; two control valves operate one set of equipment each – one valve receives a 4–12mA electrical signal, while the other receives a 12–20mA electrical signal. 5. Used to change flow characteristics.

This post was last edited by denghl on 2012-12-1 at 18:03. Reply 1# Baghdad (1): Used in important control systems where high requirements are placed on control quality, in order to improve the positioning accuracy and reliability of control valves. 　　(2) Used in applications where the pressure difference across the valve is high (△p>1MPa). By increasing the gas supply pressure to boost the output force of the actuator, it is possible to overcome the unbalanced force exerted by the liquid on the valve spool and reduce stroke error. 　　(3) When the medium being handled is at high temperature, high pressure, low temperature, or is toxic, flammable, or explosive, in order to prevent external leakage, the packing is often compressed tightly; as a result, the friction between the valve stem and the packing is high. In such cases, a positioner can be used to overcome the time delay. 　　(4) When the medium being regulated is a viscous fluid or contains solid suspensions, a positioner can overcome the resistance exerted by the medium on the movement of the valve stem. 　　(5) Used in control valves with large diameters (Dg>100mm) to increase the output thrust of the actuator. 　　(6) When the distance between the regulator and the actuator is over 60 m, a positioner can overcome the delay in the transmission of control signals, thereby improving the response speed of the valve. 　　(7) Used to improve the flow characteristics of control valves. 　　(8) When a regulator controls two actuators for step control, two positioners can be used to receive the low and high input signals respectively; thus one actuator operates at the low level while the other operates at the high level, thereby achieving step regulation.

This post was last edited by denghl on 2012-12-1 at 18:03. 1) It is used in important control systems where high requirements are placed on control quality, in order to improve the positioning accuracy and reliability of control valves. (2) Used in applications where the pressure difference across the valve is high (p>1MPa). By increasing the gas supply pressure to boost the output force of the actuator, it is possible to overcome the unbalanced force exerted by the liquid on the valve spool and reduce stroke error. (3) When the medium being handled is at high temperature, high pressure, low temperature, or is toxic, flammable, or explosive, in order to prevent external leakage, the packing is often compressed tightly; as a result, the friction between the valve stem and the packing is high. In such cases, a positioner can be used to overcome the time delay. (4) When the medium being regulated is a viscous fluid or contains solid suspensions, a positioner can overcome the resistance exerted by the medium on the movement of the valve stem. (5) Used in control valves with large diameters (Dg>100mm) to increase the output thrust of the actuator. (6) When the distance between the regulator and the actuator is over 60 m, a positioner can overcome the delay in the transmission of control signals, thereby improving the response speed of the valve. (7) Used to improve the flow characteristics of control valves. (8) When a regulator controls two actuators for step control, two positioners can be used to receive the low and high input signals respectively; thus one actuator operates at the low level while the other operates at the high level, thereby achieving step regulation.

This post was last edited by denghl on 2012-12-1 18:03 (1) It is used in important control systems where high requirements are placed on control quality, in order to improve the positioning accuracy and reliability of control valves. (2) Used in applications where the pressure difference across the valve is high (p>1MPa). By increasing the gas supply pressure to boost the output force of the actuator, it is possible to overcome the unbalanced force exerted by the liquid on the valve spool and reduce stroke error. (3) When the medium being handled is at high temperature, high pressure, low temperature, or is toxic, flammable, or explosive, in order to prevent external leakage, the packing is often compressed tightly; as a result, the friction between the valve stem and the packing is high. In such cases, a positioner can be used to overcome the time delay. (4) When the medium being regulated is a viscous fluid or contains solid suspensions, a positioner can overcome the resistance exerted by the medium on the movement of the valve stem. (5) Used in control valves with large diameters (Dg>100mm) to increase the output thrust of the actuator. (6) When the distance between the regulator and the actuator is over 60 m, a positioner can overcome the delay in the transmission of control signals, thereby improving the response speed of the valve. (7) Used to improve the flow characteristics of control valves.

This post was last edited by denghl on 2012-12-1 at 18:04. Valve positioners can increase the output capacity of control valves, reduce the delay in the transmission of control signals, speed up the movement of the valve stem, improve the linearity of the valve, overcome frictional forces on the valve stem, and eliminate the effects of unbalanced forces, thereby ensuring the accurate positioning of the control valve.

This post was last edited by denghl on 2012-12-1 18:04. 1. Improve the static characteristics of the control valve to enhance the linearity of the valve position. 2. Improve the dynamic characteristics of the control valve to reduce the delay in the transmission of control signals. 3. Change the flow characteristics of the control valve. 4. Alter the range of response of the control valve to signal pressure in order to achieve multi-stage control. 5. Reverse the direction of valve operation. Reply to 1# Baghdad

The last edit to this post was made by denghl on 2012-12-1 at 18:04. Reply 1#: The main functions of the valve positioner in Baghdad are as follows: 1. Improve the static characteristics of the control valve and enhance the linearity of the valve position； 2. Improve the dynamics of the control valve and reduce the transmission lag of control signals ； 3. Change the flow characteristic of the control valve ； 4. Change the response range of the control valve to the signal pressure in order to achieve step control ； 5. Reverse the valve’s operation.