Views: 246 Author: Site Editor Publish Time: 2021-06-20 Origin: Site
The pneumatic control valve is one of the industrial process control instruments widely used in petroleum, chemical, electric power, metallurgy, and other industrial enterprises. In chemical production, the regulating valve is indispensable in the regulating system, and it is an important part of the industrial automation system.
Pneumatic control valve uses compressed air as the power source, pneumatic cylinder as the actuator, and uses valve positioners, converters, solenoid valves, retaining valves and other accessories to drive the valve to achieve on-off or proportional adjustments and receive industrial. The control signal of the automation control pneumatic actuation system completes the adjustment of the pipeline medium: flow, pressure, temperature, and other process parameters. Pneumatic control valves are characterized by simple control, fast response, and intrinsically safe, without additional explosion-proof measures.
Pneumatic control valves are usually composed of pneumatic actuator and control valve connection installation and debugging. Pneumatic actuators can be divided into single-acting and double-acting. Single-acting actuators have return springs, while double-acting actuators have no return springs. Among them, the single-acting actuator can automatically return to the initial open or closed state of the valve when it loses its origin or suddenly fails.
Pneumatic control valves are divided into two types, namely, normally open and normally closed, according to the active form. The electric actuated globe valve is normally open or closed by the positive and negative effects of the electromagnetic valve actuator and the valve structure. The different assembly methods are realized.
Air Open Type (Normally Closed Type)
When air pressure on the membrane head increases, the motorized actuator valve moves in the direction of increasing opening. When the upper limit of input air pressure is reached, the valve is fully open. Conversely, when the air pressure decreases, the valve moves in the closing direction. When there is no air input, the valve is fully closed. Gu usually we call the air-to-open control valve a fault-closed valve.
Air-Closed Type (Normally Open Type)
The direction of its action is just opposite to the air-to-open type. When the air pressure increases, the valve moves in the closing direction; when the air pressure decreases or does not, the valve moves in the opening direction or fully opens. Gu usually we call the air-to-close control valve a fail-open valve.
The choice of air-on and air-off is based on the safety of process production. When the air source is cut off, whether the regulating valve is in the closed position or the open position is safe.
For example, for the combustion control of a heating furnace, a regulating valve is installed on the fuel gas pipeline, and the fuel supply is controlled according to the temperature of the furnace or the temperature of the heated material at the outlet of the heating furnace. At this time, it is safer to choose an air-open valve, because once the air source stops supplying, it is more appropriate for the valve to be closed than for the valve to be fully open. If the gas supply is interrupted and the fuel valve is fully opened, it will cause the danger of overheating. Another example is heat exchange equipment cooled by cooling water. The hot material exchanges heat with cooling water in the heat exchanger to be cooled. The regulating valve is installed on the cooling water pipe. The temperature of the material after the heat exchange is used to control the amount of cooling water. When the air source is interrupted, the regulating valve should be in an open position, and it is safer to use the air-closed regulating valve.
The installation position of the pneumatic control valve requires a certain height from the ground, and certain space should be left above and below the valve to facilitate the disassembly and repair of the valve. For regulating valves equipped with electric pneumatic actuators, explosion proof actuators, pneumatic valve positioners and handwheels, it is necessary to ensure convenient operation, observation, and adjustment.
