Principles of control valve selection
The control valve consists of a valve body assembly and an actuator assembly. We need to pay attention to the following five principles when selecting a control valve:
1. According to the process conditions, select the appropriate structural form and material.
2. According to the characteristics of the process object, select the flow characteristics of the control valve.
3. According to the process operation parameters, select the appropriate size of the control valve caliber.
4. According to the requirements of the process, select the required auxiliary devices.
5. Reasonable selection of implementing agencies.The response speed of the actuator should be able to meet the process
Requirements for control travel time: The selected control valve actuator should be able to meet the requirements of valve travel and process for leakage level. In some occasions, if the pressure control valve (including the vent valve) is selected, the actual possible pressure difference should be considered for appropriate amplification, that is, the actuator is required to provide a larger force. Otherwise, when an abnormal situation occurs in the process, the actual pressure difference between the front and rear of the control valve is large, and there is a danger that the valve cannot be closed or opened.
Accessories for Control Valves
In the production process, the control system puts forward various special requirements for the valve. Therefore, the control valve must be equipped with various accessories (referred to as accessories) to meet the needs of the production process. Accessories for control valves include:
1. The valve positioner is used to improve the working characteristics of the adjustment performance of the control valve and achieve correct positioning.
2. The valve position switch shows the working position of the upper and lower limit strokes of the valve.
3. When the air source of the control valve fails, keep the valve at the opening position before the air source fails.
4. The solenoid valve realizes the electromagnetic switching of the gas circuit to ensure that the valve is in the desired safe opening position when the power supply fails.
5. Handwheel mechanism When the controller of the control system fails, it can be switched to manual mode to operate the valve.
6. The pneumatic relay accelerates the action of the actuator and reduces the transmission time.
7. The air filter pressure reducer is used to purify the air source and adjust the air pressure.
8. The gas storage tank ensures that when the gas source fails, the springless cylinder and piston actuator can move the control valve to the fail-safe position. Its size depends on the size of the cylinder, the requirements of the valve action time and the working conditions of the valve.
In order to make the function of the control valve more complete and reasonable, our role in the control valve accessories cannot be ignored.