How does a control valve work?

The working principle of the control valve is to control the flow, pressure, temperature and other parameters of the fluid (liquid, gas or steam) based on the adjustment of the valve opening, so as to realize the automatic control of the industrial process. The control valve is usually used in conjunction with an automatic control system (such as a PID control system) to achieve the predetermined target by adjusting the valve opening in response to the command from the controller.

Basic steps of the working principle of the control valve:

Sensor collects information: In an industrial control system, sensors (such as pressure sensors, temperature sensors or flow sensors) monitor system parameters such as pressure, temperature or flow in real time and transmit these data to the controller of the control system.

Controller issues instructions: The controller calculates the control signal that needs to be adjusted through a feedback loop based on the difference (error) between the set target value (such as the set pressure, flow or temperature) and the actual measured value. This control signal is usually an analog signal (such as a 4-20 mA current signal) or a digital signal.

Actuator receives instructions and adjusts the valve: The control signal is transmitted to the actuator of the control valve. The function of the actuator is to adjust the valve opening according to the control signal. Actuators can be electric, pneumatic or hydraulic. They drive the movement of valves according to signals, thereby changing the path or flow of fluid through the valve.
Pneumatic actuators: commonly used in most industrial applications, use compressed air to drive valves.
Electric actuators: adjust valves through electric motors, usually used in situations where precise control is required.
Hydraulic actuators: use hydraulic pressure to control the movement of valves, suitable for high-load, high-pressure systems.

Valves regulate fluid flow or pressure: The core components of a control valve are the valve core and the valve seat. When the actuator drives the valve, the opening of the valve core changes the channel area of ​​the fluid through the valve, thereby regulating flow, pressure or temperature. For example:
If the control valve is a pressure control valve, the actuator will adjust the valve opening according to the control signal to maintain the pressure in the pipeline within the set range.
If it is a flow control valve, the control valve maintains a stable flow in the system by adjusting the opening.

Feedback and correction: The feedback mechanism in the system ensures that the action of the valve is consistent with the setting of the controller. When the system parameters (such as flow, pressure, temperature) change, the sensor will collect data again and feedback to the controller to form a closed-loop control system. The controller will correct the control signal according to the new feedback signal and adjust the valve opening to ensure that the system operates within the predetermined target range.

 
Components of the control valve:

Valve Body: The main structural part that contains the fluid, with a channel, a valve seat and a sealing part to guide the fluid flow.
Valve Plug: Cooperates with the valve seat to adjust the flow of the fluid. The valve plug changes the opening to control the flow according to the drive of the actuator.
Actuator: Responsible for driving the opening and closing of the valve plug, responding to the control signal, and controlling the opening of the valve.
Positioner: If the actuator is pneumatically driven, the positioner will ensure that the opening of the valve accurately matches the signal sent by the controller.
Feedback device: Used to feedback the actual position of the valve to the control system to ensure accurate control.

 
Common working methods of control valves:

Flow control: The control valve controls the flow of the fluid by adjusting the opening of the valve plug. In systems that require constant flow, control valves are usually used in conjunction with flow sensors.
Pressure control: The pressure control valve automatically adjusts the opening to maintain the set pressure according to the changes in the pressure in the pipeline. This type of valve is commonly found in systems such as compressed gases and liquids.
Temperature control: In thermal systems, temperature control valves maintain the temperature of the system by adjusting the heat flow. For example, in steam systems, control valves control temperature by adjusting the steam flow.
Level control: In some liquid storage systems, level control valves adjust the amount of liquid flowing in or out based on feedback from the level sensor to keep the liquid level constant.

   
The working principle of the control valve is to adjust the flow, pressure, temperature and other important parameters of the fluid by responding to the control signal through the valve actuator. The control valve is a key component in automated process control, ensuring that the industrial system operates under stable and optimized conditions by monitoring and adjusting fluid parameters in real time.