How Control Valve Works? Working Principle of Steam Control Valve скачать в хорошем качестве

How Control Valve Works? Working Principle of Steam Control Valve

A control valve is a valve operated by auxiliary power that is used to regulate or control the flow of fluids such as gas, oil, water, and steam. The auxiliary power sources can be air or electricity. It is a critical part of a control system and represents an example of the final stage of the control mechanism. Control valve is the most commonly used final control element in industrial installations today. A control valve can be operated by electric or pneumatic control. A control valve receives a signal from a control device, such as a PLC, which enables it to move for throttling or opening the flow. A control valve can regulate temperature, pressure, or flow. To do this, it requires a flow meter, pressure transmitter, or temperature transmitter. The measured value is converted into an analog signal in the control device, allowing the valve to regulate flow, temperature, or pressure according to the desired set value. A 4-20 mA or 0-10 Volt signal from the PLC may require a device that converts this electrical signal for the control valve to operate. In pneumatic systems, this device is called an electro-pneumatic positioner. A control valve consists of two separate parts: the Valve and the Actuator. Valve bodies can come in different types or styles depending on operating conditions, piping layout, and the required application. Control valves are divided into two main categories: Linear Motion and Rotary Motion. In a linear motion valve, the stem and plug move up and down. The most commonly used type of linear motion control valve is the Globe Valve. A rotary motion valve generally turns 90° to move from the open position to the closed position in most cases. A commonly used type of rotary motion valve is the 'Butterfly or Ball Valve.' An actuator is a power unit connected to the valve that provides the necessary force to open and close it. As previously mentioned, an actuator can be controlled electrically or pneumatically. The most common and most reliable type of actuator is the 'Pneumatic Actuator.' Control valve receives a signal from a control device, such as a PLC, to operate. The control device compares the actual flow rate to the desired flow value, known as the set point. The control device generates an output signal to move the valve in order to bring the flow rate to the set point value. Due to the structure of pneumatic actuators, they are designed to remain in either the open or closed position in case of a loss of control signal, thanks to the internal springs. As air pressure increases, the diaphragm applies more force on the spring, pushing the valve stem and plug into the seat. As air pressure decreases, the opposite movement occurs. If the control signal is lost, the control valve returns to its initial position, which is known as the 'fail-safe mode.' The type of fail-safe mode is determined as either normally open or normally closed, depending on the application in which the control valve is used. When calculating actuator power, the generated air or electrical power is determined to overcome the spring force. In the event of a power loss to the actuator, the electrical or pneumatic force is no longer available, and the spring force pushes the valve to open or close. You may wonder how much the valve opens or closes in percentage and proportion when the flow rate changes. This depends on the 'percentage change in flow rate' and several factors such as pipe diameter, flow rate, and velocity. Additionally, the control device must be configured to respond correctly to any changes in flow rate. This is typically achieved using PID control within the PLC or control device.