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Solution when the stability of the inlet regulating valve is poor

1) Change the direction of the imbalance force
In the stability analysis, when the unbalanced force is known to be the same as the valve closing direction, that is, when the valve is closed, the valve stability is poor. When the valve is operated under the above-mentioned unbalanced force condition, the method of changing the direction of action is selected, and the flow-closing type is usually changed to the flow-open type, and the stability problem of the valve can be conveniently solved in general.

2) Avoid the unstable working method of the valve itself
Some valves are limited by their own structure and have poor stability when working at certain opening degrees. 1 double seat valve, the opening is less than 10%, due to the flow at the ball, the lower ball is closed, which brings instability; 2 the slope of the unbalanced force changes near the alternating, and its stability is poor. For example, the butterfly valve has an alternating point of about 70 degrees; the double seat valve has an opening of 80 to 90%. In the case of such a valve, the stability in the unstable zone is inevitably poor, and the unstable zone can be avoided.

3) Replace the valve with good stability
Valves with good stability have less variation in unbalanced force and good guidance. Among the commonly used ball valves, the sleeve valve has this large feature. When the stability of single and double seat valves is poor, the stability of replacing the sleeve valve will be improved.

4) Increase the spring stiffness method
The ability of the actuator to resist load changes affecting the stroke depends on the spring stiffness. The greater the stiffness, the smaller the effect on the stroke and the better the valve stability. Increasing the spring stiffness is a common simple method to improve the stability of the valve. For example, the spring of 20-100KPa spring range is changed into a large-stiff spring of 60-180KPa. This method is mainly a valve with a positioner. Otherwise, the used The valve should be equipped with a positioner.

5) Reduce the response speed method
When the system requires the response valve to respond or adjust the speed should not be too fast, the response and adjustment speed of the valve is faster, such as the flow needs to be fine-tuned, and the flow adjustment of the regulating valve changes greatly, or the system itself is fast response The system and the regulating valve have a positioner to speed up the valve action, which is disadvantageous. This will produce overshoot, vibration, etc. In this regard, the response speed should be reduced. The methods are as follows: 1 change the linear characteristic to logarithmic property; 2 can be changed to converter and relay with positioner.

6) Symmetrical bolting, using a thin gasket sealing method
In the structure of the "O" ring seal regulating valve, when a thick gasket with a large deformation (such as a winding sheet) is used, if the compression is asymmetrical, the force is asymmetrical, and the seal is easily broken, inclined, and deformed. Serious impact on sealing performance. Therefore, in the repair and assembly of such valves, the compression bolts must be tightened symmetrically (note that they cannot be tightened at one time). It is better if the thick gasket can be changed into a thin gasket, which is easy to reduce the inclination and ensure the seal.

7) Method of increasing the width of the sealing surface to prevent the flat valve spool from jumping and reducing the leakage amount thereof
Flat valve spools (such as two-type valves, valve plugs for sleeve valves) have no guiding and guiding surfaces in the valve seat. Because the valve is working, the spool is subjected to lateral force and flows out from the flow side. Fang, the larger the clearance of the valve core, the more serious the unilateral phenomenon, plus the deformation, the different center, or the small chamfer of the valve sealing surface (usually guided by 30° chamfer), so when the valve is closed, the valve core seal is generated. The chamfered end face is placed on the sealing surface of the valve seat, causing the spool to jump when closed, or even not in place, so that the leakage of the valve is greatly increased. The simplest and most effective solution is to increase the size of the sealing surface of the valve plug so that the minimum diameter of the end face of the valve core is 1 to 5 mm smaller than the diameter of the seat. It has sufficient guiding effect to ensure that the valve core is guided into the valve seat and kept. Good sealing surface contact.

8) Change the flow direction, solve the problem of promoting the clearance, and eliminate the surge method
The two-position valve is usually used as a flow-close type to improve the cutting effect. For the liquid medium, due to the function of the flow-close type unbalanced force, the valve core is closed, and the lifting effect is also called the suction action, which accelerates the movement speed of the valve core and generates a slight water hammer, which causes the system to surge. The solution to the above phenomenon is that as long as the flow direction is changed to flow, the surge can be eliminated. Similar to this problem, which affects the valve and does not work properly, it can also be considered to solve this problem.

9) Overcoming the fluid damage method
The most typical valve is a two-seat valve. The fluid enters from the middle, the spool is perpendicular to the inlet, and the fluid flows around the spool into two groups. The fluid impinges on the valve core so as to lean against the outlet side, causing friction, damaging the guide surface of the valve core and the bushing, resulting in malfunction, and high flow rate can also cause the valve core to bend, erode, and even break when severe. Solution: 1 increase the hardness of the material of the guiding part; 2 increase the middle size of the upper and lower balls of the valve core to make it thick; 3 use other valves instead. If a sleeve valve is used, fluid flows from around the sleeve and the lateral thrust to the plug is greatly reduced.

10) Method for overcoming the rotation of the valve core by overcoming the rotational force generated by the fluid
For the "V" shaped spool, due to the asymmetry of the inflow of the medium, the tangential force of the spool acting on the "V" shaped port is inconsistent, producing a rotational force that causes it to rotate. Especially for valves with DN ≥ 100. As a result, the valve may be disengaged from the actuator push rod connection, and the springless actuator may cause the diaphragm to twist. The solution is as follows: (1) turn the counterclockwise rotation direction by an angle to balance the tangential force acting on the valve core; 2 further lock the connection between the valve stem and the push rod, and if necessary, add an anti-rotation splint; 3 Replace the "V"-shaped open valve plug with a plunger-shaped valve core; 4 use or change to a sleeve-type structure; 5, if the rotation caused by resonance, eliminate the resonance to solve the problem.

11) Adjust the friction of the butterfly valve plate to overcome the opening and jumping method
The soft-sealed butterfly valve of "O" ring, seal ring, lining, etc., when the valve is closed, due to the deformation of the soft seal, the valve plate is closed in place and encloses the valve plate, which can achieve a very good cutting effect. However, when the valve is to be opened, the force of the actuator to open the valve plate is continuously increased, and when the frictional force of the soft seal to the valve plate is increased, the valve plate is activated. Once activated, this friction is drastically reduced. In order to achieve the balance of force, the valve plate is opened violently, and when the force is balanced with the opening torque of the medium of the corresponding opening degree and the opening torque of the actuator, the valve stops at this opening. This violent and sudden opening can be opened up to 30 to 50%, which will cause a series of problems. At the same time, due to the large change of the soft seal when it is closed, it is prone to permanent deformation or being crushed or strained by the valve plate, which affects the service life. The solution is to adjust the friction of the soft seal to the valve plate, which not only ensures the required cut-off requirements, but also enables the valve to start normally. Specific measures include: 1 adjusting the interference; 2 by limiting or adjusting the pre-tightening force and output force of the actuator to reduce the difficulty caused by the excessive closing of the valve plate.

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