Weak current College】 【control valve selection and maintenance-of-Power By】 【China power house network.

First, the control valve selection

A, the importance of the control valve selection

Control valve is automatic control system of the actuator, its application quality direct response in the system of quality. As process control terminal symbol, its importance than in the past have been updated. Control valve applications or bad quality, except for the product itself, the user is correctly installed, use, maintain, correct calculation and selection are very important. Because the selection of the mistake, resulting in the system can stop, or even putting-, so for users and system designers should recognize the importance of the valve at the scene, you must control valve selection caused enough attention.

B, the principle of control valve selection

1, according to the technological conditions, select the appropriate structure and materials.

2, according to the technological characteristics of the object, select a control valve's flow characteristics.

3, according to the process operation parameters, select the appropriate control valve diameter size.

4, according to the requirements of the process, select the auxiliary device.

5. reasonable choice. Executive Body of the response should be able to meet the technological

To control the travel time of the request: the selection of control valve actuator should be covered with foot valve stroke and technology on the disclosure of rating requirements. In some occasions, such as selection pressure control valve (valve), consideration should be given to the actual possibility of pressure differential for appropriate amplification, which requires implementing agencies can provide larger forces. Otherwise, when the exception occurred on technology, the control valve before and after the actual pressure differential is large, occur off not or can not be opened.

Second, the control valve accessories

In the production process control system for valve raise various kinds of special demand, therefore, the control valve must be equipped with various ancillary installations (annex) to meet the needs of the production process. Control valves accessories including:

1, valve positioner for improved control valve performance characteristics, realization of the right positioning.

2, valve position switch to display the upper and lower limits of the valve stroke work location.
3, pneumatic control valve-valve when sources of failure, keep the valve is in the air source fails before the opening position.

4, solenoid valve for gas solenoid switch, guarantee the valve in a power failure while the valve is in the desired security opening location.

5. hand wheel mechanism when control system controller fails, you can switch to manual mode operation valve.

6, pneumatic relay enables executing agency action to speed up and reduce transfer times.

7. air filter regulator used to purify the air source, adjust the air pressure.

8, storage tank guarantee when the source of failure, so no spring of cylinder piston executive agencies to be able to work will control valve action to fail safe location. Its size depends on the size of the cylinder, valve action time requirements and the working conditions of the valve and so on.

In short, the role of the attachment is to make the control valve function better, smarter and more complete.

Third, the control valve maintenance

Control valve has a simple structure and action simple and reliable, but because it has a direct contact with the process media, its properties directly affect the system's quality and environmental pollution, control valve must be regular maintenance and periodic maintenance, especially for the use conditions and important occasions, should pay more attention to maintenance work. Focus inspection site

1, valve wall

For use in high-voltage differential and corrosive media in the control valve, the valve interior, diaphragm valve of diaphragm is often affected by the impact and corrosive media, must be focused on checking the pressure resistance, corrosion resistance.

2, valve seat

Control valve, due to media infiltration, fixed seating surface with thread within the vulnerable to corrosion, check for loose seat should be noted. The high differential pressure of the valve under work, you should also check whether the flush valve seat sealing surface.

3. the valve

The valve is regulating the work of moving parts, the media's most serious erosion, corrosion, maintenance time to seriously check valve parts are corrosion, wear, particularly in the high differential pressure of the valve wear more serious (due to cavitation phenomenon), it should be noted. When the valve damaged should be replaced, in addition you should also note the stem if there is a similar phenomenon, or loose with the valve connection.

4, diaphragm "O"-rings and gaskets. Should check control valve diaphragm, "O"-shaped gasket degradation, fissure damage.

5, sealing packing

It should be noted that PTFE packing and sealing grease degradation, combined with surface damage, should be replaced when necessary.