Views: 289 Author: Site Editor Publish Time: 2021-06-13 Origin: Site
The air actuated 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. The common forms of regulating valve mainly include control ball valve, butterfly valve for flow control and pneumatic angle seat valve.
Pneumatic control valve uses compressed air as power source, cylinder as actuator, and uses electrical valve positioner, converter, air actuated solenoid valve, retaining valve and other accessories to drive the valve. In this way, the switch or proportional adjustment is realized, and the control signal of the industrial automation control system is received to complete the adjustment of the pipeline medium: flow, pressure, temperature and other process parameters.
Pneumatic control valve is characterized by simple control, fast response, and intrinsic safety. In addition, the feature of the pneumatic control valve that does not require additional explosion-proof measures is different from the explosion proof valve actuator and the explosion proof electric actuator.
Pneumatic control valve is usually composed of pneumatic actuator and control valve connection installation and debugging. Pneumatic actuators can be divided into single-acting and double-acting types. There is a return spring in the single acting actuator, and there is no return spring in the double acting actuator. Pneumatic control valve is divided into air-open type and air-close type according to the action form.
The installation position of the pneumatic control valve requires a certain height from the ground. There must be a certain space above and below the valve for valve disassembly and repair.
The regulating valve should be installed on a horizontal pipeline and vertical to the pipeline up and down. Generally, it should be supported under the valve to ensure stability and reliability.
The working environment temperature of the regulating valve should be between -30～+60, and the relative humidity should not be greater than 95%.
There should be straight pipe sections before and after the regulating valve. The length is not less than 10 times the pipe diameter (10D) to avoid the valve straight pipe section from being too short and affecting the flow characteristics.
When the caliber of the regulating valve is different from that of the process pipeline, a reducing pipe should be used for connection.
The control valve must be thoroughly cleaned of foreign matter in the pipeline before installation, such as dirt, welding slag, etc.
1. The regulating valve does not operate. First confirm whether the air source pressure is normal, and look for the air source failure. In this case, the valve must be removed for further inspection.
2. The regulating valve is jammed. If the reciprocating stroke of the valve stem is slow, there may be sticky substances in the valve body, coking and blocking or packing too tight, or the PTFE packing is aged, the valve stem is bent and scratched. In such a situation, you can quickly open and close the auxiliary line or regulating valve, so that the stolen goods will be washed away by the medium from the auxiliary line or regulating valve.
3. Leaking valve. Regulating valve leakage generally includes internal leakage of the regulating valve, packing leakage, and leakage caused by the deformation of the valve core and valve seat. There are different ways to deal with these three situations.
4. Control the oscillation of the valve. Since there are many reasons for the oscillation, specific problems should be analyzed in detail. For example, for slight vibration, we increase the stiffness of the regulating valve to eliminate it. As for the severe vibration of the pipe and the base, the vibration interference can be eliminated by adding supports.
5. The regulating valve is noisy. When the fluid flows through the regulating valve, if the pressure difference between the front and rear is too large, cavitation will occur to the valve core, valve seat and other parts, causing the fluid to produce noise. There are several ways to eliminate noise: eliminate resonance noise, eliminate cavitation noise, thick-walled pipelines, sound-absorbing materials, tandem silencers, soundproof boxes, tandem throttles, and low-noise valves.
