Solution to electric regulating valve

Electric regulating valve, also known as control valve, is a control element in the process control industry of industrial automation. It is mainly used to change the material flow, working pressure, temperature, liquid level meter, etc. by receiving the control signal from the control module and relying on the actual operation of the driving force. - It is generally composed of electric actuators and gate valves. Because of its weight, it is difficult to select the right valve, which is often thankless and also involves system commissioning, adjustment quality, air pollution, etc.

1. Change the direction of the unbalanced force
In the stability analysis, when the unbalanced force is known to act in the same direction as the valve closing direction, that is, when the valve has a closing tendency, the valve stability is poor. When the valve works under the above unbalanced force conditions, the method of changing its direction of action is adopted, usually changing the flow closing type to the flow opening type, which can generally solve the stability problem of the valve easily.

2. The working method of the free valve's stable zone
Some valves are limited by their structure and have poor stability when working at certain openings.
For double-seat valves, the opening is within 10%, because the flow is open at the upper ball and closed at the lower ball, which brings instability problems;
The stability is poor near the alternating slope of the unbalanced force change. For example, the alternation point of the butterfly valve is about 70 degrees; the double-seat valve is at 80~90% opening. When encountering such a valve, the stability is inevitably poor when working in an unstable area. Avoid working in an unstable area.

3. Replace the valve with good stability
The valve with good stability has a small change in unbalanced force and good guidance. Among the commonly used ball valves, the sleeve valve has this major feature. When the stability of the single and double seat valves is poor, replacing them with sleeve valves will improve the stability.

4. Increase the spring stiffness method The ability of the actuator to resist the influence of load changes on the stroke depends on the stiffness of the actuator. The greater the stiffness, the smaller the influence on the stroke, and the better the stability. Increasing the spring stiffness is a common and simple method to improve stability, such as changing the spring with a spring range of 20 ~ 100KPa to a spring with a large stiffness of 60 ~ 180KPa. This method is mainly used for valves with positioners. Otherwise, the valve used must be equipped with a positioner.

5. Reduce the response speed method When the system requires the response of the valve or the adjustment speed should not be too fast, the valve response and adjustment speed are relatively fast. For example, the flow needs to be adjusted, but the flow adjustment of the valve is very large, or the system itself is a fast response system, but the valve is equipped with a positioner to speed up the action of the valve. This is not good, it will cause overshoot and vibration. In this regard, the response speed should be reduced. There are ways to change the linear characteristic to a logarithmic characteristic; the valve with a positioner can be changed to a converter or a relay.
6. Tighten bolts symmetrically and use thin gaskets to seal. In the "O" ring sealing regulating valve structure, when using thick gaskets with larger shapes (such as winding sheets), if the compression is asymmetrical, the seal will be easily damaged, tilted, and deformed, which will seriously affect the sealing performance. Therefore, when repairing and assembling such valves, the bolts must be tightened symmetrically (note that they cannot be tightened at once). It would be better if the thick gasket could be changed to a straight gasket, which would make it easy to reduce the inclination and ensure the seal.

7. Increase the cover width and reduce leakage. Flat valve cores (such as valve plugs of two-position valves and sleeve valves) have no guide and guide curved surface in the wide seat. When the valve is working, the valve core is subjected to lateral force and moves from the inflow side to the outflow side. The larger the valve core matching clearance, the more serious this unilateral phenomenon is. In addition, the chamfer of the shape, the center, or the center-adjusting sealing surface is small (- usually 30% chamfer for guidance), so when it is close to closing, the chamfered end face of the valve core sealing surface is placed on the wide seat sealing surface, causing the valve core to beat when closing, or even not close in place at all, greatly increasing the valve leakage. The solution is to increase the size of the valve core sealing surface so that the smaller diameter of the center-adjusting end face is 1~5mm larger than the valve seat diameter, with sufficient guiding effect to ensure that the valve core is guided into the valve seat and maintain good sealing surface contact.

8. Change the flow direction to solve the problem of promoting closing. Position valves are usually used as flow-closing types to improve the cutting effect. For liquid media, the unbalanced force of the flow-closing type presses the core to close, which has a closing-promoting effect, also known as suction, which speeds up the action speed of the core, produces a light water hammer, and causes system surge. The solution to the above phenomenon is to change the flow direction to flow-open, and the surge can be eliminated. This method can also be considered to solve the problem that the valve cannot work normally due to the closing-promoting effect.

9. Overcoming fluid damage method
The typical valve is a double-seat valve. The fluid enters from the middle, the valve core is perpendicular to the inlet, and the fluid bypasses the valve core and flows out in two streams. The fluid impacts the valve core and leans against the outlet side, causing friction and damage to the guide surface of the valve core and the village sleeve, resulting in abnormal operation. High flow may also cause the valve core to bend, erode, and even break in severe cases.
Solution:
Increase the hardness of the material of the guide part;
Increase the middle size of the upper and lower balls of the valve core to make it coarse;
Select other valves as a substitute. If a sleeve valve is used, the fluid flows in from the sleeve around, and the lateral thrust on the valve plug is greatly reduced.

10. Methods to overcome the rotational force generated by the fluid to rotate the core
For the valve core with a "V"-shaped opening, due to the asymmetry of the medium inflow, the tangential force acting on the valve core on the "V"-shaped opening is inconsistent, generating a rotational force that causes it to rotate. This is especially strong for the DN2100 valve. As a result, the connection between the valve and the actuator push rod may be disconnected, and the springless actuator may cause the diaphragm to twist.
The solutions are:
Turn the valve core in the opposite direction of rotation by an angle to balance the tangential force acting on the valve core;
Further, pin the connection between the valve stem and the push rod, and if necessary, add an anti-rotation splint;
Replace the valve core with a "V"-shaped opening with a plunger-shaped valve core;
Use or change to a sleeve-type structure;
If the rotation is caused by resonance, eliminating the resonance can solve the problem.