Knowledge of pneumatic control valve

by:Lianke Valve     2022-08-08
I have introduced some knowledge about pneumatic control valves before, and here I will introduce some other knowledge about pneumatic control valves. Pneumatic control valve is to use compressed air as the power source, the cylinder as the actuator, and with the help of electric valve positioner, converter, solenoid valve, retaining valve and other accessories to drive the valve, to achieve on-off or proportional adjustment, receiving industrial The control signal of the automatic control system is used to adjust the pipeline medium: flow, pressure, temperature and other process parameters. Pneumatic control valve is characterized by simple control, fast response, and intrinsic safety, without the need for additional explosion-proof measures. Pneumatic regulating valve is usually composed of pneumatic actuator and regulating valve connection, installation and debugging. Pneumatic actuator can be divided into two types: single-acting and double-acting. There is a return spring in the single-acting actuator, while there is no return spring in the double-acting actuator. . Among them, the single-acting actuator can automatically return to the open or closed state initially set by the valve in the event of loss of origin or sudden failure. The pneumatic control valve is divided into two types: air-opening and air-closing according to the action form, the so-called normally open type and normally closed type. The air-opening or air-closing of the pneumatic control valve is usually through the positive and negative action of the actuator and the valve state structure. of different assembly methods. Pneumatic control valve action mode: air open type (normally closed type) is when the air pressure on the membrane head increases, the valve moves in the direction of increasing the opening degree, and when the upper limit of the input air pressure is reached, the valve is in a fully open state. Conversely, when the air pressure decreases, the valve moves in the closing direction, and when no air is input, the valve is fully closed. Gu usually we call the air-to-open control valve a fail-closed valve. The action direction of the air-to-close type (normally open type) is just opposite to that of the air-to-open type. When the air pressure increases, the valve moves to the closing direction; when the air pressure decreases or does not, the valve moves to the opening direction or fully opens. Gu usually we call the air-to-close control valve a fail-open valve. The choice of air opening and air closing is considered from the safety point of view of process production. When the air supply is cut off, whether the regulating valve is in the closed position safety or the open position safety. Valve positioner The valve positioner is the main accessory of the regulating valve, which is greatly used in combination with the pneumatic regulating valve. It accepts the output signal of the regulator, and then uses its output signal to control the pneumatic regulating valve. The displacement is fed back to the valve positioner through a mechanical device, and the valve position is transmitted to the upper system through an electrical signal. Valve positioners can be divided into pneumatic valve positioners, electro-pneumatic valve positioners and intelligent valve positioners according to their structure and working principle. The valve positioner can increase the output power of the regulating valve, reduce the transmission delay of the regulating signal, speed up the movement speed of the valve stem, improve the linearity of the valve, overcome the friction force of the valve stem and eliminate the influence of unbalanced force, thereby ensuring the adjustment Correct positioning of the valve. The actuators are divided into pneumatic actuators and electric actuators, which are divided into straight stroke and angular stroke. It is used to automatically and manually open and close various cutting doors, wind panels, etc. Pneumatic control valve installation principles (1) The installation position of the pneumatic control valve requires a certain height from the ground, and there must be a certain space above and below the valve to facilitate the disassembly and repair of the valve. For regulating valves equipped with pneumatic valve positioners and handwheels, it must be easy to operate, observe and adjust. (2) The regulating valve should be installed on the horizontal pipeline, and the upper and lower sides should be perpendicular to the pipeline. Generally, it should be supported under the valve to ensure stability and reliability. For special occasions, when the regulating valve needs to be installed horizontally on a vertical pipeline, the regulating valve should also be supported (except for the small-diameter regulating valve). When installing, avoid adding additional stress to the regulating valve). (3) The working environment temperature of the regulating valve should be (-30~+60), the relative humidity should not be greater than 95% 95%, and the relative humidity should not be greater than 95%. (4) There should be a straight pipe section at the front and rear of the regulating valve, and the length should not be less than 10 times the pipe diameter (10D), so as to avoid the straight pipe section of the valve being too short and affecting the flow characteristics. (5) When the diameter of the regulating valve is not the same as that of the process pipeline, it should be connected with a reducer. Threaded connections can be used when installing small-diameter control valves. The fluid direction arrow on the valve body should be consistent with the fluid direction. The above is an introduction to other knowledge points of pneumatic control valves. If you have any questions, you can consult Lianke Valve Co.,Ltd. at any time. Tel: +86-577-8585 9626.
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